Chemistry exam 1
Properties of Low Density Polyethene
- Low density n - Relatively Soft - Low melting point - Non crystalline - opaque - Non conductor of electricity
Properties of esters
- Smaller esters are liquids at room temperature. They are good solvents for many organic compounds. Many esters are large molecules and exist as oils and waxes
allotropes of carbon
- diamond - graphite - amorphous carbon
Esters define - general formula and how are they formed
An ester functional group consists of a carbonyl (C--O) group with a second oxygen bonded to the carbon atom to form -COO- General formula of an ester is R-COO-R' where R and R' are alkyl groups, which may or may not be identical. Esters are formed when carboxylic acids are heated with alcohols in the presence of sulfuric acid. Sulfuric acid acts as a catalyst as it increases the rate of reaction, but is not consumed by the reaction.
Polymer properties
As the size of the molecule increases the melting point of the polymer increases. The weak dispersion forces between the long polymer chains are sufficiently strong to cause polyethene to be a solid at room temperature. In general polymers are also - lightweight - non conductors of electricity - durable - versatile - acid resistance - flammable
Methane formula and importance
CH4 first series of alkanes
define unsaturated hydrocarbons
Carbon compounds with hydrogen in which there are double or even triple bonds between the carbon atoms.
Boiling points of carboxylic acids
Carboxylic acids have higher boiling points than you might expect from their molecular masses. The high boiling points are a direct result of the presence of hydrogen bonds between carboxylic acid molecules. Hydrogen bonding between two carboxylic molecules results in the molecules forming a dimer (two identical molecules bonded together) The formation of dimers between two carboxylic acids is one of the reasons carboxylic acids have higher boiling points.
exceptions to the subshell notation
chromium and copper
what forces result from the attraction between positive and negative charges
electrostatic
first ionisation energy
energy required to remove one electron from an atom
stem names
meth (1) Eth (2) prop (3) but (4) pent (5) hex (6) hept (7) oct (8) non (9) dec (10)
define atomic number
number of protons
ways to modify a metal
- through alloy production - by heat treatment - with a coating
Alkanes famalies
Each member of the alkane series differes from the previous member by a -CH2- unit. A series of molecules in which each member differs by -CH2- from the previous member is known as a homologous series
Plastic and polymers
For chemists the word plastic describes a property of a material, no the material itself. A substance is described as being plastic if it can be molded into different shapes readily. This is because the material from which it is made is a plastic material.
Define isomers
Molecules that have the same molecular formula but have different arrangements of atoms are said to be structural isomers of each other. The more atoms in the molecule, the more possible isomers there are
polypropene
addition polymer made from propene. The way the CH3 side chains are arranged effect the properties od the polymer.
define alkanes
alkanes are hydrocarbons that contain only one single bond. All the carbon-carbon bonds in alkanes are single covalent bonds. Molecules such as this are said to be saturated. General formula in picture
define monatomic
elements which exist as individual atoms. Also known as noble gases because they are chemically inert.
empirical formula
gives the simplest whole number ratio fo elements in the compound
graphene
graphene is best described as a single layer of graphite It is a single layer sheet with the same arrangement as those stacked in graphite Graphite is soft, due to the weak dispersion forces between its layers. Graphene is only a single layer and retains the electrical conductivity of graphite but it is an extremely strong and tough material. Every carbon atom is available for reaction from two sides at any instant during a chemical reaction (because of singly layer arrangement)
periodic table
groups- vertical periods- horizontal
reactivity of non metals
non metals undergo reactions to gain electrons
electronegativity
the ability of an atom to attract electrons towards itself. The greater the core charge, the greater the electronegativity
nanotchnology
use of technologies that manipulates and investigate properties of materials on the nanoscale
light energies in the emission spectra
violet= high energy, as the colour changes to blue, green, yellow and orange the energy decreases. Red light is the lowest
large surface area of nanoparticles importance
- adsorption of molecules: the large surface area means that even small volume can absorb a large number of molecules. Therefore, they can be used to remove unwanted chemicals and gases - transportation of molecules: the small size and large surface area of nanoparticles means that they can transport chemicals through air, skin and cells. This means that they can be used in medicine for transporting drugs - catatlysts: the surface's of some nanoparticles can be sued to increase chemical reactions. They speed up the reaction but aren't consumed by the reaction. The large surface area of nanoparticles means that many of the reactions can take place at the same time, which increases the rate of reaction
electrons in the same shell
- are about the same distance from the nucleus -have about the same energy
info from the emission spectra
- atoms of the same element produce identical line spectra - each element has a unique line and therefor a unique electronic strcuture
advantages of polymers
- available in different forms with different properties - chemically resistant and corrosion resistant - easy to process - have a low density - good mechanical strength - properties can be modified - many can be recycled
forming nanomaterials
- bottom-up method uses specifically designed molecules or atoms in chemical reactions to gradually build up the new nano particles from the smaller atoms or molecular units - top-down method uses the larger bulk material as the starting material. The bulk material is broken down into nano particles by mechanical or chemical means
why does carbon form more compounds than all other elements combined
- carbon has four valence electrons so carbon can potentially form covalent bonds with four different atoms - Carbon atoms can form strong covalent bonds with other carbon atoms - the covalent bonds formed can be a combination of single, double or triple bonds
Thermosetting polymers
- decompose or burn when heated. - Do no soften because the bonds between the chains are very strong. If the temperature becomes high enough to break the covalent bonds, the breaks may be at any point, causing the polymer to decompose. It is difficult to recycle thermosetting polymers as they cannot be remoulded into new shapes.
the bohr model proposed:
- electrons revolve around the nucleus in fixed, circular orbits - The electrons' orbits correspond to specific energy levels in the atom - electrons can only occupy fixed energy levels and cannot exist between two energy levels - orbits of larger radii correspond to energy levels of higher energy
ionic compound properties
- have a high melting and boiling point - they're solid at room temperature - are hard, but brittle, so they're not malleable or ductile - don't conduct electricity in solid state - are good conductors of electricity in liquid state or when dissolved in water - they vary from very soluble to insoluble in water, they're not soluble in non-polar solvents (oil)
state properties of non metals
- have a range of melting points and have a high boiling point - good conductors of electricity - good conductors of heat - generally have high densities - are malleable- can be shaped by beating or rolling - are ductile- can be drawn into wire - are lustrous when cut or polished - are hard with high tensile strength - low ionisation energies and electronegativities
polypropene properties
- isotatic: the side groups on one side allow crytalline regions to form and there's attraction between chains (used to make AUS money) - atatic- side groups randomly distributed which prevents the side chains from stacking together and forming crystalline regions - syndiotatic- alternationg side groups which allows good packing and material is high crytalline
properties of nanoparticles
- large surface area compared to volume - small size and unique structure mean they can be used to develope composite (made up of several parts) nanomaterials. - When a substance is processed into nanoparticles its physical, chemical and optical properties change - nanoparticles interact differently with light (used in sunscreens)
naming esters
- locate the functional group and the carbonyl carbon - Starting from this carbon, determine the number of carbon atoms in the chain attached to it. Name it according to the stem name, adding the suffix -'oate'. The carbonyl- containing portion of the ester is derived from the carboxylic acid. - the alkyl group bonded to the single bonded oxygen atom is then added in front of the name. This portion of the ester is derived from the alcohol
disadvantages of polymers
- many are derived from a non renewable resource - microorganisms can't break down the polymers - thermoplastic polymers have a limited thermal stability - some plastic products crack, scratch or break easily - many plastics make toxic gases like hydrogen chloride when burned - some plasticisers can leach out of containers - thermosetting polymers are currently difficult to recycle
naming carboxylic acids
- names of carboxylic acids end with the suffix - oic acid - the carbon in the fucntional group is counted in the cahin used to name the carboxylic acid - the carboxyl carbon is always carbon number 1
alkanes properties
- non-polar molecules. As a result, they are insoluble in water and the only attractive force between the molecules is dispersion forces. As the number of carbons and the size of the molecules increases with this homologous series, the strength of the dispersion forces increases, so the melting and boiling points of the alkanes increases
molar mass: - of an element - of a compound
- of an element is the mass of one mole of the element - of a compound is the mass of one mole of the compound. It's equal to the RMM or RFM * it's symbol is M and unit is gmol-1
forms of metallic nanomaterials
- particles - rods - wires - tubes
reactions of alkanes
- tend to be relatively unreactive, although like most hydrocarbons, they can be used as a fuel. - The reaction between a fuel and oxygen is known as combustion - If supply of oxygen is plentiful, the products of combustion will be carbon dioxide and water. (aka complete combustion)
Themoplastic polymers
-Soften when heated, which means they can be remolded or recycled. -Polymers are only thermoplastic if the bonds between the long polymer chains are hydrogen bonds, dipole-dipole bonds or weak dispersion forces. - When heated the molecules in thermoplastic materials have enough energy to overcome the intermolecular forces and become free to move and slip past one another. If the polymer can be remoulded, then it can probably be recycled easily, a desirable property.
Reactions of alkenes
-undergo combustion in a plentiful supply of oxygen - the greater reactivity of a carbon-carbon double bond compared with a single bond enables alkenes to also take part in addition reactions.
Naming alkenes and alkynes
1. Identify the longest unbranched carbon chain. For aklenes, the chain must inculde the double bond and for alkynes the chain must include the triple bond 2. Number the carbon atoms in the chain from the end of the chain that will gice the smallest numbers to double bonded or triple bonded carbon atoms and to branching groups 3. Name the alkyl groups after the alkane from which which they are derived. 4. Identify the postition of the double bond or triple bond by the number of the first carbon atom involved in the bond. Use the suffix '-ene' to indicate the presence of a double bond. Use the suffic '-yne' to show the presence of a triple bond 5.List the number and position of each of the alkyl groups at the beginning of the compound's name in alphabetical order 6. If two identical side chains are present, use 'di-' as a prefix, for three use 'tri'
extracting iron using blast furnace steps
1. as the air rises through the furnace and meets the descending charge, oxygen reacts with coke to produce carbon dioxide, which then reacts further with the coke to produce carbon monoxide. This releases heat energy and helps to maintain the high temperature that provides the fast rate of reaction required for metal production in the furnace. 2.Extraction of iron from iron oxide occurs in a series of steps in which carbon monoxide is the main reactant. The steps occur in different temperature zones within the blast furnace. Iron ore is first converted to another iron oxide and then finally to the metal. 3. Holes at the bottom of the furnace are opened and the molten iron and slag are drained out and separated.
naming alkanes
1. identify the longest unbranched carbon chain 2. Number the carbon atoms in the chain from the end of the chain that will give the smallest numbers to branching groups 3. Name the alkyl groups after the alkane from which they are derived 4. Place the number and position of each of the alkyl groups at the beginning of the compound's name 5. If two identical side chains are present, use di- as a prefic, for three use tri 6 If there are alkyl side chains of different lengths on the molecule, list them in alphabetical order at the start of the name, with their numbers to indicate respective positions
what does each property say about the structure of metals 1. are hard and tend to have high boiling points 2. conduct electricity in solid and molten liquid state 3. are malleable and ductile 4. have high densities 5. good conductors of heat 6. are lustrous or reflective 7. react by losing electrons
1. strong electrostatic forces of attraction between positive metal ions and the sea of delocalised electrons holds the metallic lattice together 2. free-moving delocalised electrons will move towards a positive electrode and away from a negative electrode in an electric circuit 3. when a force causes metal ions to move past each other, layers of ions are still held together by the delocalised electrons between them 4. the cations in a metal lattice are closely packed. The density of a metal depends on the mass of the metal ions, their radius and the way in which they are packed in the lattice 5. When the delocalised electrons bump into each other and into the metal ions, they transfer energy to their neighbour. Heating a metal gives the ions and electrons more energy and they vibrate more rapidly. The electrons, being free to move, transmit this energy rapidly throughout the lattice 6. The presence of free electrons in the lattice, metals reflect light of all wavelengths and appear shiny 7.the delocalised electrons in metals may participate in reactions anywhere on the metal's surface. The reactivity of a metal depends on how easily electrons can be removed from its atom
the nucleus of an atom is approximately -- times smaller than the size of the atom
10000-100000
electrons are -- times smaller than a neutron (or neutron)
1800 times smaller than a proton or a neutron
copolymers
2 or more monomers held together by one polymer
Homologous series
A series of molecules in which each member differs by -CH2- from the previous member is known as a homologous series. Compounds that are members of the same homologous series have - a similar structure - a pattern to their physical properties - similar chemical properties - the same general formula
define alkyl groups
A side group attached to a straight chain. Alkyl groups have one less hydrogen atom than the corresponding alkane of the same name so the general formula of an alkyl group is C(n)H(2n+1) eg. Methyl and ethyl When writing the condensed structural formula of a branched alkane, alkyl groups are written in brackets.
Addition polymerisation
Alkenes undergo an addition reaction with themselves to produce long chains. The reaction of the monomer ethene with itself to form polyethene, the addition polymerization process. Large square brackets and the subscript n, are used to simplify the drawing of long polymer molecules. Since all the atoms of the monomers are present in an addition polymer, the empirical formula of the monomer is the same as that of the polymer
Alkynes
Alkynes are a homologous series of hydrocarbons with one carbon-carbon triple bond. General formula is C(n)H(2n-2) presence of triple bond makes them unsaturated molecules. Simplest is ethyne. Next member differs by a CH2 unit
Esterification reaction
An ester functional group is formed from the esterification reaction between the carboxyl functional group of the carboxylic acid and the hydroxyl functional group of the alcohol. Since water is also formed during this reaction, it is also called a condensation reaction
Carboxylic acids define
An important class of organic compounds. These compounds are weak acids and can be identified by the presence of a carboxyl group (-COOH) General formula is RCOOH, where R is an alkyl group such as -CH3 and C2H5.
Elastomers
An interesting class of polymers that are formed when only occasional cross links are present. The chains in these polymers can still move past each other when stretched by the cross-links return the chains to their original positions once the force causing the stretching is released. Elastic bands and other rubber items are made of elastomers. The cross links stop elastomers from completely melting when heated and makes recycling difficult.
dispersion forces
Dispersion forces are caused by temporary dipoles in the molecules that are the result of random movement of the electrons surrounding the molecule. These temporary dipoles are also known as instantaneous dipoles. Dispersion forces are always present between molecules, no matter whether they are polar or non-polar as electrons are constantly in motion within atoms.
properties of metals
Exhibit a range of melting points and relatively high boiling points Are good conductors of electricity Are good conductors of heat Generally have high densities Are malleable - they can be shaped by beating or rolling Are ductile - they can be drawn into a wire Are lustrous or reflective when freshly cut or polished Are often hard with high tensile strength Have low ionisation energies and electronegativities However not all metals have all of these properties Mercury is a liquid at room temperature (low melting point) The group 1 elements (the alkali metals) are all soft enough to be cut with a knife and they react vigorously with water to produce hydrogen gas. Both mercury and group 1 elements exhibit most of the other properties listed above.
emission spectra
Heating an element can cause an electron to absorb energy and jump to a higher energy state. Shortly afterwards the electron returns to the lower energy state, releasing a fixed amount of energy as light. Electrons may return directly to the ground state or may move to other energy levels before returning to the ground state. - when atoms are heated, they give off electromagnetic radiation or light. If the light passes through a prism, it produces a spectrum with a black background and a number of colored lines known as line spectra or emission spectra. Each emission spectrum is unique for a particular element and can be used to identify different elements.
High density polyethene
Highly specialised transition metal catalysts, known as ziegler-natta catalysts are used to avoid the need for high pressures. The polymer molecules are produced under milder conditions and there are very few branches. The lack of branches allows the molecules to pack together tightly, increasing the density and the harness of the polymer formed. The arrangement of the polymer molecules in more ordered, resulting in crystalline sections. This form of polyethene is known as high density polyethene
Alkenes
Homologous series of hydrocarbons with at least one carbon-carbon double bond. General formula is C(n)H(2n) The double bonds makes them unsaturated molecules. More reactive than alkanes. Simplest is ethene, the next member in the series differs by a CH2 unit. All alkenes are non-polar and do not dissolve in water
Addition reactions
In addition reactions, part of the reactant becomes bonded to one carbon in the double bond and the other part of the reactant becomes bonded to the other carbon atom in the double bond. The double bond is broken and a single C-C bond is formed.
carboxylic functional group
In this functional group, a carbon atom has a double bond to one oxygen atom and a single bond to a second oxygen atom. The second oxygen atom is also bonded to a hydrogen atom. This -COOH group can be regarded as replacing one hydrogen in the structure of an alkane. The bonds around the carbon atom have a trigonal planar arrangement with the O-C-C angle being about 120.
abundance and properties of carbon
Is a vital component of all living systems Is the 11th most abundant element in the universe Has three isotopes 12C, 13C, 14C Has one of the higherst melting points of any elemt. It undergoes sublimation, changing from a solid state directly to a gas state at temperatures above 3550*C Is a non-metal, but a number of forms can conduct electricity Can form single, double and triple covalent bonds with several other elements Can form large molecules and lattice structures by bonding to itself
elements that are alloyed with iron to make steels
Manganese - increases strength and toughness Chromium- increases hardness and tensile strengths, resists corrosion Nickel - increases toughness, tensile strength and hardness, resists corrosion Cobalt - improves magnetic properties, resists high temperatures Not considered interstitial alloys, as the added atoms are too big to fit into the spaces in the metallic lattice. The atoms of the elements added replace some of the iron cations and the mixture is called a substitutional alloy
quenching (process, effect on structure and properties)
PROCESS: A metal is heated to a moderate temperature and cooled quickly (sometimes by plunging into water) EFFECT ON STRUCTURE: Tiny metal crystals form EFFECT ON PROPERTIES: The metal is harder and brittle
annealing (process, effect on structure and properties)
PROCESS: a metal is heated to a moderate temperature and allowed to cool slowly EFFECT ON STRUCTURE: Large metal crystals form EFFECT ON PROPERTIES: the metal is softer with improved ductility
tempering (process, effect on structure and properties)
PROCESS: a quenched metal is heated (to a lower temperature than is used for quenching) and allowed to cool EFFECT ON STRUCTURE: crystals of intermediate size form EFFECT ON PROPERTIES: the metal is hard but less brittle
define polymers
Polymers are very long molecules formed from the linking of a large number of small molecules, called monomers.
Graphite
STRUCTURE: Covalent layer lattice, each carbon bonded to three other carbons, one delocalized electron per atom. There are strong covalent bonds between the carbon atoms in each layer. However, there are weak dispersion forces between the layers. As a consequence, it is hard in one direction but quite slippery and soft in another direction. PROPERTIES:Conductive Slippery Soft Greasy material USES: Lubricant Penciles Electroduces Reinforcing fibres
Diamond
STRUCTURE: Covalent network lattice, each carbon surrounded by four other carbon atoms in a tetrahedral arrangement,there are no weak intermolecular forces present, only strong covalent bonds. This is what gives diamond its strength PROPERTIES: Very hard Sublimes Non-conductive Brittle USES: Jewellery Cutting tools drills
Amorphous carbon
STRUCTURE:Irregular structure of carbon atoms. Many varieties exist with many different, non-continuous packaging arrangements. PROPERTIES: Conductive Non crystalline cheap USES: Printing ink Carbon black filler Activated charcoal photocopying
subshell notation
SUBSHELLS: first shell contains only s, second contains s,p and third contains s, p, d and so on. ORBITALS: s has one orbital, p has 3 orbitals, d has 5 orbitals, f has seven orbitals. The total number of orbitals in a shell is given by n^2.
define allotropes
Some elements can exist with their atoms in several different structural arrangements called allotropes, that give them different physical forms. In different alloltropes, the atoms are bonded to each other in different, specific ways. This gives them significantly different properties from other allotropes of the same element
Low density Polyethene
The earliest method of producing polyethene involved high temperatures and extremely high pressures. Under these harsh conditions, the polymer is formed too rapidly for the molecules to be neat and symmetrical. The presence of these branches impacts upon the properties of the polymer as the molecules cannot pack closely together. The dispersion forces between molecules are weaker when the molecules are further apart. The arrangement of the polymer molecules can be described as disordered or non-crystalline. This form of polyethene is known as low density polyethene.
V-shaped or bent
The four electron pairs repel each other to form a tetrahedral arrangement. This causes the two hydrogen atoms to form a shape or bent arrangement with the oxygen atom. With two lone pairs in the molecule, the two single covalent bonds are pushed closer together. LONE PAIRS: 2 ANGLE: slightly less than 109.5 Eg. Water
Solubility of carboxylic acids
The functional group can be said to be made up of a carbonyl group (C--O) and a hydroxyl group (-OH). Both of these groups are polar, with oxygen being much more electronegative than carbon and hydrogen. The electrons are drawn away from the hydrogen atom, enabling it to react in water to form an H+ ion, so the functional group can act as an acid. When dissolved in water, hydrogen bonding occurs between the carboxyl group of carboxylic acids and water molecules, making them more soluble than alcohols in water. The solubility decreases as carboxylic acids increase in size. A longer carbon chain means that more of the molecule is non polar.
Alcohol functional groups
The functional group in alcohols is made up of an oxygen atom bonded to a hydrogen atom. This -OH group is known as a hydroxyl group and replaces on hydrogen in the structure of an alkane. Successive members of this homologous series differ by a -CH2- unit
Percentage composition of organic compounds
The percentage composition of a compound tells you the proportion by the mass of the different elements in that compound. To determine the percentage composition by mass of a compound, divide the mass of each element present by the mass of the whole sample and express the result as a percentage (mass of the element present/total mass of the compound)*100
Structural isomers of alcohols
The position of the OH functional group influences the chemical and physical properties of alcohols. Alcohols with more than two carbon atoms have more than one positions where the hydroxyl functional group may be.
Structural isomers of esters
The position of the ester functional group is shown by the naming of the ester, rather than by using numbers. A series of carboxylic acids also has the same molecular formula.
why are metals lustrous
The presence of free electrons in the lattice, metals reflect light of all wavelengths and appear shiny
strength of dispersion forces
The strength of dispersion forces increases as the size of the molecule increases. Larger molecules have a larger number of electrons. Therefore it is easier to produce temporary dipoles in molecules with large numbers of electrons. Since larger molecules have stronger dispersion forces, they have higher melting and boiling points
properties of graphite
The strong covalent bonds between the atoms in each layer explain graphite's resistance to heat. Graphite sublimes at a temperature of 3600*C Each carbon atom is bonded to three other carbon atoms. The fourth valence electron from each atom is above to move within the layer. The electrical conductivity of graphite is due to these delocalised electrons
Naming alcohols
To name an alcohol, start with the name of the parent alkane, remove the e from the end and add the suffix ol. THe atoms in the longest carbond chain are numbered from the end that is closest to the functional group. The number of the carbon atom to that the hydroxyl group is bonded is shown before the ol ending and is seperatred by hyphens
properties of transition metals
Transition metals generally have unfilled d-subshells and are often referred to as the d-block. Their properties include They tend to be harder They have higher densities They have higher melting points Some of them have strong magnetic properties The hardness, higher densities and higher melting points are due to the atoms of transition metals generally being a smaller size due to their greater core charge. This allows them to pack together more tightly with stronger bonds
application of carbon nanomaterials
Up to 300 times stronger than steel (used in sporting equipment) Better conductors of electricity than silver (nanotubes are wires that are much narrower than metal wire can be used to miniaturise electrical circuits) Better thermal conductors than diamond. Could be used to transfer heat away from electrical components
Define crackling process
Used in the processing of crude oil. Heavier crude oil fractions undergo crackling. This process breaks the larger hydrocarbon molecules into smaller molecules using heat and a catalyst. The smaller molecules and especially those with carbon-carbon double bonds are needed by the petrochemical industry
why are metals good conductors of heat
When the delocalised electrons bump into each other and into the metal ions, they transfer energy to their neighbour. Heating a metal gives the ions and electrons more energy and they vibrate more rapidly. The electrons, being free to move, transmit this energy rapidly throughout the lattice
trigonal planar
a central atom has two single bonds and one double bond, then the three sets of bonds will repel each other to get maximum separation. This results in a molecular shape known as trigonal planar because the atoms form a triangle in one plane LONE PAIRS: 2 ANGLE: 120 Eg. Methanal
molecular compounds
a diatomic molecules contains two atoms. Covalent bonds can also form between atoms of different elements
double bonds, triple bonds and VSEPR
a double bond contains two pairs of electrons. A triple bond contains three pairs of electrons. The VSEPR theory treats double and triple bonds in the same way that it treats single bonds and lone pair electrons
explain high melting points of ionic compounds
a large amount of energy is needed to overcome the electrostatic attraction between oppositely charged ions and allow them to move freely. Therefore, the ionic bonds between the positive sodium ions and negative chloride ions must be strong, which explains why a high temperature is required to melt solid sodium chloride
nanomaterial definition
a material with nanoscale definition
define haematite
a mineral containing iron. Composed of iron oxides with the formula Fe2O3. Haematite is the main source of iron ore in Australia. It is dark and reflective when polished but a red layer forms on its surface after exposure to oxygen.
metallic nanowires
a nanowire is a nano-sized wire. Nanowires are much longer than nanorods
metal crystals
a single metal crystal is a region in a solid where the particles are arranged in a regular way. A sample of solid metal consists of many small crystals. Each crystal is a continuous regular arrangement of cations surrounded by a sea of delocalised electrons, but the arrangement of individual crystals with respect to one another is random. Regular lattice arrangements are disrupted at the point where one crystal meets another. smaller crystals result in harder metals as there is less free movement of layers in cations over each other. Smaller crystals also have more areas of disruption between them, and this usually means that these metals will be more brittle. Faster cooling leads to smaller crystals; slower cooling allows more time for crystals to grow large.
explain hardness and brittleness of ionic compounds
a strong force is needed to disrupt the crystal lattice, which means that it's very hard. Although a salt crystal is hard, a strong force will shatter the crystal, meaning it's brittle. This is because layers of ions will move relative to each other due to the force of blow. During this movement, ions of like charge shift so they are next to each other. The repulsion between the similarly charged ions causes the crystal to shatter
electronegativity across a period and down a group
across a period= increases as number of occupied shells stays the same and the core charge increases, so the valence electrons are strongly attracted to the nucleus down a group= decreases number of shells increases, so valence electrons are less strongly attracted to the nucleus and are further away
core charge across a period and down a group
across a period= increases because the valence electrons are more attracted to the nucleus as the core charge increases down a group= stays the same but the valence electrons are held less strongly as they're further away from the nucleus
define isotopes
all atoms that belong to the same element have the same number of protons (same atomic number), but not all atoms that belong to the same element have the same mass number
explain brittleness of ionic compounds
although a salt crystal is hard, a strong force such as a hammer blo will shatter the crystal. Therefore, it is said to be brittle. This is because the layers of ions will more relative to each other due to the force of the blow. During this movement, ions of like charge are shifted so they are next to each other. The resulting repulsion between the similarly charged ions causes the crystal to shatter.
define substitutional alloy
an alloy made from elements of similar chemical properties and size. The metallic elements added to make substitutional alloys have fairly similar chemical properties and form cations of a similar size to the main metal. Eg. stainless steal is a substitutional alloy of nickel and chromium.
atomic structure
atoms have a positively charged nucleus surrounded by negatively charged electrons. Within the nucleus, there are 2 particles: protons (positively charged) and neutrons (no charge)
octet rule
atoms lose, gain or share valence electrons in order to have a full outer shell
why do ionic compounds not have a molecular formula
because they don't exist as molecules, but they do have empirical formula
electron dot diagram - best used for - limitation
best used for: Determining the formula of the molecule and the type of bonds Limitations: does not show the relative size of atoms or shape of the molecule
valence diagram - best used for - limitation
best used for: Simplifying the electron dot diagram limitation:does not show the relative size of atoms or shape of the molecule
ball and stick model - best used for - limitation
best used for: displaying the molecule shape limitation: shows the shape but not the relative sizes of the atoms
space-filling model - best used for - limitation
best used for: showing the relative size and position of the atoms in the molecule limitation: Shows the relative size and position of the atoms but does not show bond angles or types of bonds
biodegradable plastics
break down naturally, most are condensation polymers. Another approach is adding additives that promote degradation. Example: polyvinyl alcohol
size of side group on monomer
bulky ones naje it hard for the chains to slide over each other and stack together, which prevents the formation of crytalline regions that refract light and amorphous materials are made.
nanotubes
closely related to graphene. They are called nanotubes because they have a long, hollow structure with walls formed from graphene. Long but small in diameter. Can be capped on the end of each cylinder by a half fullerene molecule Can be single walled or multiwalled. A multiwalled nanotube has smaller tubes sitting inside larger tubes. PROPERTIES Strong Can conduct heat and electricity Strong forces of attraction to eachother
cross links
covalent bonds between polymer molecules are called cross-links. Cross links limit movement between the polymer molecules and make the polymer rigid, hard and heat resistant. Thermosetting polymers are used to make items such as saucepan handles, bowling balls and shatterproof crockery
polarity of polyatomic molecules
determining the polarity of molecules with more than two atoms is a little more complicated. This is because the polarity of polyatomic molecules depends on the shape of the molecule as well as the polarity of the covalent bonds. As the general rule Symmetrical molecules are nonpolar Asymmetrical molecules are polar
electron shells
different energy levels. The orbit in which an electron moved depended on the energy of the electron. Electrons with low energy are in orbits close to the nucleus while high-energy electrons are in outer orbits
dipole dipole forces
dipole-dipole forces only occur in polar molecules. These forces result from the attraction between the positive and negative ends of the polar molecules. Dipole-dipole forces are relatively weak since the partial charges on the molecules are small. However, the more polar a molecule is, the stronger the dipole-dipole forces are. The polarity will be larger when there is a large difference in the electronegativities of the atoms or a large asymmetry in the shape of the molecule
polyethene chain length
dispersion forces are much stronger in longer chains of polyethene
reactivity of non metals down a group and across a period
down a group= decreases as it's harder for a non-metal to attract electrons into valence shell with a greater amount of shells across a period= increases as the increasing core charge makes it easier for a non metal to attract electrons
first ionisation energy down a group and across a period
down a group= decreases as the core charge is constant and the number of shells increases, the valence electrons are less attracted to the nucleus and the energy to overcome this attraction is less across a period= increases as the core charge increases and the number of occupied shells stays the same, so the valence electrons are strongly attracted to the nucleus and more energy is needed to overcome this energy
atomic radius down a group and across a period
down a group= increases as core charge stays constant and the number of shells increases, so the atomic radii increases across a period= decreases as number of occupied shells is constant while the core charge increases. the valence electrons are more attracted to the the nucleus
metallic character down a group and across a period
down a group= increases as it is easier for a metal with a greater number of shells to lose electrons across a period= decreases as the increasing core charge makes it more difficult to lose electrons
conductive polymers
electrically conductive polymers, it happens when double and single bonds are alternated
polarity of diatomic molecules
electronegativity is the key factor that determines the electron distribution in diatomic molecules. Electronegativity is the tendency of an atom in a covalent bond to attract electrons.
non polar molecules
even molecules with polar covalent bonds can be non-polar if the molecule is symmetrical The symmetry of the molecules means that the individual dipoles of the covalent bonds cancel each other perfectly. The result is a molecule with no overall dipole. It is non-polar
blast furnace
extraction of iron from ore and the removal of unwanted materials is carried out in a tall, bottle-shaped tower called a blast furnace. These furnaces are heated to very high temperatures, pre-heated air is blasted into the bottom part of the furnace, while solid 'charges' (scoops) of iron ore, coke and limestone are continuously added to the top. The construction of the furnace causes different temperature zones where different reactions can take place.
additives
few polymers are used in the pure form, most have additives that improve properties. For example adding colour, UV stablisers, pasticisers
why do metals conduct electricity in solid and molten states
free-moving delocalised electrons will move towards a positive electrode and away from a negative electrode in an electric circuit
properties as a result of alloy production
generally, an alloy is harder and melts at a lower temperature than the pure metal. This is because atoms of different sizes are now included in the metal lattice. As these atoms do not pack in the same way as the main metals, they will not allow the lattice to shift and bend in the same way. This disruption of the regular metallic lattice also accounts for the lowered melting point. In interstitial alloys, a small proportion of an element with significantly smaller atoms is added to a metal. The added atoms sit in interstices between metal cations in the metallic lattice.
work hardening
hammering or working cold metals causes the crystals to rearrange as they are pushed and deformed. This can result in the hardening of the metal as the crystals are flattened out and pushed closer together.
hydrogen bonding in water
he fact that ice is less dense than liquid water can be explained by hydrogen bonding. Water has two hydrogen atoms attached to an oxygen atom in a V-shape. Therefore, the hydrogen atoms can form hydrogen bonds with the lone pairs of electrons on the oxygen atoms of neighbouring molecules. In this way, a water molecule can form hydrogen bonds with four other water molecules. The hydrogen bonding holds the water molecules in ice in a regular crystal lattice. In this lattice, the molecules are held further apart than in liquid water. As a result, ice is less dense and therefore floats in liquid water.
Alcohol boiling points
higher boiling points - the boiling points of alcohols increases as the size of the alcohol molecule increases. However, the boiling points of the alcohols are all higher than those of the corresponding alkanes. All the alcohols are liquids at room temperature, in contrast to the alkanes and alkenes, many of which are gases. The higher boiling point is due to the presence of the OH group, which allows hydrogen bonding to occur between molecules and strengthens the intermolecular bonding.
saturated hydrocarbons
hydrocarbons with only single bonds. Carbons are 'saturated' with hydrogen as they are bonded to as many hydrogens as possible
hydrogen bonding
hydrogen bonding is a special form of dipole-dipole force. Hydrogen bonding only occurs between molecules in which a hydrogen atom is covalently bonded to an oxygen, a nitrogen or a fluorine atom. Oxygen, nitrogen and fluorine atoms are small and highly electronegative. Therefore, they strongly attract the electrons in a covalent bond. This creates a significant partial positive charge on a hydrogen atom bonded to these atoms. The partial positively charged hydrogen atom is then attracted to lone pairs of electrons in the nitrogen, oxygen and fluorine atoms of neighbouring molecules. Remember that hydrogen only has one electron and this electron is strongly attracted to the N, O or F atom in the covalent bond. The exposed positively charged hydrogen (proton) is attracted to a lone pair on a nitrogen, oxygen or fluorine atom in another molecule. The result is a relatively strong intermolecular bond that is approximately ten times stronger than a dipole-dipole bond but about one-tenth the strength of an ionic or a covalent bond. The presence of hydrogen bonds results in higher melting and boiling points.
polyatomic molecules
if the atoms of one element have a different number of valence electrons from the atoms of the element it is bonding with, the molecules that if formed may not be a simple diatomic molecule. Molecules made up of more than two atoms are called polyatomic molecules. Two examples of polyatomic molecules are water and methane
polar diatomic molecules
if the covalent bond is between atoms of two different elements, then the electrons will stay closer to the most electronegative atoms as it has a stronger pull on the electrons in the bond. Molecules with an imbalanced electron distribution are said to be polar. All diatomic molecules that are made up of atoms with different electronegativities are polar to some extent. The level of polarity will depend on the difference between the electronegativities of the two atoms. The greater the difference between the electronegativities, the greater the polarity of the molecule
non-polar diatomic molecules
if the two atoms in a covalent bond are the same (have identical electronegativities) then the electrons are shared equally between the two atoms. This is the case for diatomic molecules such as chlorine, oxygen, hydrogen and nitrogen Bonds with an equal distribution of valence electrons are said to be non-polar because there is no charge on either end of the molecule
how are dispersion forces started
in a molecule, the electrons are constantly moving. In the case of a non-polar molecule, such as fluorine, the electrons spend an equal amount of time around each atom. Occasionally, the electrons gather more closely together at one end of the molecule, causing one end of the molecule to become negative and the other end to become positive. This is known as a temporary dipole. These temporary dipoles can then induce dipoles in the neighbouring molecules The neighbouring molecules then induce dipoles in their neighbours and so on. The temporary dipoles attract each other to create the intermolecular forces known as dispersion forces.
electron pair repulsion
in general, atoms in covalent molecules are most stable when they have eight electrons in their valence shell. This is known as the octet rule. These eight electrons are arranged into four pairs of electrons. Not all electron pairs in molecules exist as covalent bonds. Some electrons form a nonbonding pair of electrons known as a lone pair of electrons. In the VSEPR theory, lone pairs of electrons are treated in the same way as electron pairs in covalent bonds in order to determine the shape of a molecule.
hardness of covalent molecular substances
in general, covalent molecular substances tend to be softer than ionic or metallic substances. Wax, putty and butter are typical examples of soft, covalent molecular substances. These substances are soft because the intermolecular forces holding the molecules together are weak. Therefore, the bonds between the molecules can be readily broken and the substances can be easily moulded, scratched or crushed.
define intersitial alloy
in interstitial alloys, a small proportion of an element with significant smaller atoms is added to a metal. The added atoms sit in interstices between metal cations in the metallic lattice.
explain electrical conductivity of ionic compounds
in solid form, ions are held in the crystal lattice and are not free to move, therefore don't conduct electricity. When solids melt, the ions become free to move, enabling the cations and anions in the molten compound to conduct electricity. When they dissolve in water, ionic bonds in the lattice break and the ions are separated and move freely. When an electric current is applied, + ions move towards the - charged electrode and - ions move towards the + charged electrodes
explain electrical conductivity of ionic compounds
in the solid form, ions in sodium chloride are held in the crystal lattice and are not free to move, so solid sodium chloride does not conduct electricity. Remember that for a substance to conduct electricity it must contain charged particles that are free to move. When solid ionic compounds melt, the ions become free to move, enabling the cations and anions in the molten compound to conduct electricity. Similarly, when ionic compounds dissolve in water, ionic bonds in the lattice are broken and the ions are separated and move freely in solution.
molecular formula
indicates the number of atoms of each element in one molecule of substance. It gives the actual number of atoms of each element
electronegativity and polarity of covalent molecular substances
intermolecular forces are an example of electrostatic forces. The electrostatic attraction between molecules works in a similar way. In intermolecular forces, the electrostatic attraction is between positive and negative charges in the molecules. These charges appear as a result of uneven electron distributions within the molecules. The following section examine how the shape of the molecule and the electronegativity of its atoms can cause these uneven electron distributions.
what is iron ore?
iron ore is a mineral that occurs in the Earth's crust. Iron ore is composed mainly or iron oxide combined with rocky material. The iron must be extracted from the ore before it can be used to make steel.
define ionic compounds
made by the chemical combination of metallic and non-metallic elements
plasticisers as addidives
makes the polymer molecules move further apart, weakening their forces between the chains, s the chains slide past each other and making the material softer
relative formula mass
mass of a formula unit relative to the mass of an atom of carbon 12 taken as 12 units exactly. It's numerically equal to the atomic masses of the elements in the formula
relative molecular mass
mass of one molecule of that substance relative to the mass of a carbon 12 atom taken as 12 units exactly
define compounds
materials containing different types of atoms in fixed ratios. The atoms in compounds can form molecules or large networks of atoms
define elements
materials containing just 1 type of atom. Some non metals form a covalent network lattice. Some non metallic elements are monoatomic which means they exist as individual atoms. They're known as noble gases, as they're unreactive
core charge
measure of attractive force felt by the valence shell electrons towards the nucleus CC= number of protons - number of total inner shell electrons
atomic radius
measurement for the size of the atom. aka the distance from the nucleus to the valence shell electrons
mass spectrometer
measures relative isotopic mass and isotopic abundance
cation
metal atoms lose electrons to non metallic atoms and become positively charged metal ions
the ionic bonding model
metal atoms lose electrons to non-metallic atoms and so become positively charged metal ions (cations) Nonmetal atoms gain electrons from metal atoms and so become negatively charged non-metal ions (called anions) Large numbers of cations and anions combine to form a three-dimensional lattice The three dimensional lattice is held together strongly by electrostatic forces of attraction between the oppositely charged ions. The electrostatic forces of attraction holding the ions together is called ionic bonding
reactivity of metals and transition metals with oxygen
metals also react with oxygen. Group 1 metals all react rapidly with oxygen. While transition metals are less reactive with oxygen than the metals in group 1 and 3 reactions still usually occur.
reactivity of metals with acids
metals are normally more reactive with acids than with water. Group 1 is most reactive, down a group reactivity increases
coatings
metals can be given a coating in order to make them even more suitable for their intended application. Surface coatings: tin, paint and powder coating, protect the steel by forming a physical barrier on the surface to prevent exposure to damaging chemicals Powder coating: finely ground particles of pigment and resin sprayed on electrostatically Galvanising: laying zinc on steel to prevent rusting, zinc will react with oxygen and carbon dioxide in the air to slow corrosion.
reactivity of metals and transition metals in water
metals in group 1 of the periodic table are more reactive in water than those is group 2 down a group, the reactivity of the metal in water increases Transition metals are generally less reactive with water than group 1 and 2 metals are.
what is a mineral
minerals are naturally occuring solid substances with a definite chemical composition, structure and properties.
counting by weighing
n(amount in mol)=m (mass in g)/ M (molar mass in g mole-1)
max number of electrons in each shell
n1=2 n2=8 n3=18 n4=32 n=2n^2
relationship between number of particles and amount of substance in mole
n=N(number of particles)/Na(amount of substance)
metallic nanorods
nanorods are nanoscale rods in which each dimension ranges from 1 to 100nm. Nanorods of metals such as gold and silver have been synthesised in the lab. Their applications include display tech, microelectronics, power of solar cells to mobiles
electrostatic attraction
negative attracts positive. Electrons are bound to the nucleus by this force to the protons in the nucleus. The charge of an electron is equal but opposite to the charge of a proton
anions
non metal atoms gain electrons from metal atoms and became negatively charged non metal ions
covalent bonding
non metallic atoms have a relatively high number of electrons in their outer shells and they tend to share rather than to transfer electrons. Covalent bonding occurs when electrons are shared between non metallic atoms.
mass spectrum: - number of peaks - horizontal axis - vertical axis
number of peaks= number of isotopes horizontal axis= relative mass of each isotope vertical axis= the abundance of each isotope
define mass number
number of protons and neutrons
alloy production
often metals are mixed with small amounts of another substance, usually a metal or carbon. The substances are melted together, mixed and then allowed to cool. The resultant solid is an alloy. By varying the composition of alloys, you can obtain materials with specific properties.
metric units of length from smallest to largest
picometre, nanometre, micrometre, millimetre, centimetre, metre, kilometre
plastic waste
plastics have useful properties for use, but have a serious environmental impact as the biodergation is very slow
the only metals found in the earth's crust that are found entirely in their elemental state...
platinum and gold. They are so unreactive they are considered chemically inert. They do not generally react with water, acids or oxygen.
crude oil
produced by the effects of heat and pressure on dead animals, plants and microorganisms trapped in the Earth's crust and buried beneath the sediment formed over millions of years
non polar monomers
properties of a polymer depend on the monomer used to make them. Tetrafluroethen is made when all of the hydrogens of ethene are replaced by electronegative fluorine. Molecules react together to form a polymer: polytetrafluroethene (Teflon) which is different from ethene
the prefix nano refers to...
refers to one billionth or 10-9 in scientific notations.
properties of diamond
single covalent bonds between carbon atoms are strong bonds. The entire structure of a diamond consists of a continuous network of these bonds, making diamond very hard and rigid. There are no small molecules in diamond, so there are no weak forces between the atoms. There are only strong covalent bonds between carbon atoms and this makes the sublimation point very high The rigidity means that diamonds are brittle and break rather than bend Diamond does not conduct electricity ebcause it does not contain any charged particles that are free to move Because the atoms in diamonds are held together very strongly, the thermal conductivity is extremely high.
explain solubility of ionic compounds
some ionic compounds are very soluble in water, whereas others are very insoluble. When a soluble ionic compound is added to water, the ions break away from the ionic lattice and mix with the water molecules. If an insoluble compound is added to water, the ions remain bonded together in the ionic lattice and do not form a solution Whether an ionic compound is soluble or insoluble depends on the relative strength of the forces of attraction between the: - Positive and negative ions in the lattice - Water molecules and the ions
nanoparticles
specific type of nanomaterial with unique properties and a broad range of applications. They're usually spherical and used in chemotherapy and sunscreen as industrial catalysts
Why are metals hard and tend to have high boiling points
strong electrostatic forces of attraction between positive metal ions and the sea of delocalised electrons holds the metallic lattice together
valence shell electron pair repulsion theory
the VSEPR theory is based on the principle that negatively charged electron pairs in the outer shell of an atom repel each other. As a consequence, these electron pairs are arranged as far away from each other as possible
mole is...
the amount of substance and is given the symbol n
why does the number of protons have to be equal to the number of electrons
the atom is electrically neutral and therefore for it to be neutral there needs to be an equal amount of protons and neutrons
define organic chemistry
the branch of chemistry that studies the chemistry of carbon compounds
why do metals have high densities
the cations in a metal lattice are closely packed. The density of a metal depends on the mass of the metal ions, their radius and the way in which they are packed in the lattice
PVC
the chlorine atoms introduce dipoles int he long molecules. This increases the strength of the forces between polymer molecules, which leads to a higher melting point. PVC offers other advantages over polyethene: it has a low electrical conductivity and low flammability. A PVC item burning in a flame will extinguish itself when it is removed from the flame. Used in - water pipes and the covering of electrical wiring
why do metals tend to react by losing electrons
the delocalised electrons in metals may participate in reactions anywhere on the metal's surface. The reactivity of a metal depends on how easily electrons can be removed from its atom
ionisation energy
the energy needed to remove an electron from an atom. The first electron to be removed has the lowest ionisation energy and is therefore the easiest to remove.
intermolecular forces
the forces that exist between molecules.
intramolecular forces
the forces that hold atoms together within a molecule
linear shape
the four electron pairs repel each other to form a tetrahedral arrangement. Therefore, the hydrogen and fluorine atoms form a linear molecule. LONE PAIRS: 3 Eg. Hydrogen fluoride If the central atom has two double bonds, then the two double bonds repel each other. This results in a linear molecule like Carbon dioxide. LONE PAIRS: 4 Eg. Carbon dioxide If the central atom has a single bond and a triple bond, as in hydrogen cyanide then the molecule is also linear LONE PAIRS:1 Eg. Hydrogen cyanide ANGLE:180
pyramidal
the four electrons pairs repel each other to form a tetrahedral arrangement. However, the lone pair is ignored when determining the shape of a molecule. Instead, the three hydrogen atoms are described as forming a pyramidal arrangement with the nitrogen atom. The lone pair occupies slightly more space than the bonding electrons, so the three single covalent bonds are pushed closer together. LONE PAIRS: 1 ANGLE: slightly less than 109.5 Eg. Ammonia
relative isotopic mass
the mass of an atom of that isotope relative to the mass of an atom of carbon 12 HYDROGEN- 1 proton, 0 neutrons total is 1 mass of atom relative to carbon 12 is 1/12= 1 HELIUM- 2 protons, 2 neutrons total is 4 mass of atom relative to carbon 12 is 4/12=4
limitations of the metallic bonding model
the metallic bonding model doesn't explain Range of melting points, hardness and densities of different metals Differences in electrical conductivities of metals Magnetic nature of metals such as cobalt,iron and nickel
valence electrons
the outermost shell of an atom is known as the atom's valence shell. The electrons in the outer shell are called valence electrons
relative isotopic abundance
the percentage abundance of an isotope in the natural environment
heat treatment (the three types)
the physical properties of a metal can be altered by controlled heat and cooling. The three main methods are annealing, quenching and tempering.
covalent molecular substances
the physical properties of covalent molecular substances are primarily determined by the strength of the forces between the molecules. These forces are known as intermolecular forces. The shape of a molecule is one factor that determines the strength of intermolecular forces. However, the covalent bonds inside the molecules also play an important role.
polarity and solubility
the polarity of a molecular substance has a significant impact on its solubility. In general, substances that are polar tend to dissolve in polar solvents. Non-polar substances tend to dissolve in nonpolar solvents.
Alcohols solubility
the presence of the oH group allows hydrogen bonds to form between water molecules and alcohol molecules. For the smaller alcohols, such as methanol and ethanol, this allows the alcohol to dissolve readily in water. The solubility of the other alcohols decreases as the length of the carbon chain attached to the -OH group increases. A longer carbon chain means that more of the molecule is non-polar and the molecule becomes less polar overall.
percentage composition tells you...
the proportion by mass of the different elements in that compound
dipole definition
the separation of the positive and negative charges is known as an electric dipole, or simply as a dipole as they have two oppositely charged poles at each end of the molecule. In asymmetrical molecules, the individual dipoles of the covalent bonds do not cancel each other. This results in a net dipole, making the overall molecule polar
dipole dipole and boiling point
the stronger the dipole-dipole forces, the higher the melting and boiling points. This is because dipole-dipole forces bond the molecules together in the solid or liquid. Stronger dipole-dipole forces require more energy (higher temperatures) to break these bonds and change the solid to a liquid or the liquid to a gas.
nanoscience
the study of nanoparticles and nanotechnology. Nanotechnology is the use of technologies that manipulate and investigate the properties of materials on the nanoscale.
adsorption definition
the term is used when a molecule attaches to a surface of a solid or liquid. Different from absorption, where molecules are incorporated into the substance
explain hardness of ionic compounds
there are strong electrostatic forces of attraction between ions in an ionic compound, so a strong force is needed to disrupt the crystal lattice. Therefore, one of the properties of ionic compounds is that they are hard. This means that a sodium chloride crystal cannot be scratched easily
explain high melting points of ionic compounds
they have high melting points because a large amount of energy is needed to overcome the electrostatic attraction between the oppositely charges ions and allow them to move. So, the ionic bonds between the + and - ions is strong.
chromium and copper exceptions define
they occur in the transition metals, whose electron configurations allow them special chemical properties such as multiple valence states. This all occurs due to the fact that the 4s and 3d orbitals are extremely close in energy. Usually the 4s orbitals will fill (contains 2 electrons) before the 3d orbital begins to fill. This is not the case in Cu and Cr. CHROMIUM - Having one electron in each of the energetically similar orbitals is more favourable than having the 4s orbitals filled and one of the 3d orbitals left unfilled 1s2 2s2 2p6 3s2 3p6 3d5 4s1 COPPER - Is more stable with a completely full 3d subshell and a partially filled 4s then the other way around 1s2 2s2 2p6 3s2 3p6 3d10 4s1 SUBSHELLS ARE MORE STABLE EITHER FULL OR HALF FULL
crytallinity
things made from polymers have many long chains with intermolecular forces and many have crystalline regions (chains like up in a normal arrangement, which makes the bonds stronger and they prevent transmission of light) and amorphous regions (randomly tangled, they are less rigid, weaker and see through)
fullerenes
this allotrope was made up of molecules containing a roughly spherical group of carbon atoms arranged in a series of pentagons and hexagons, similar to the shape of a soccer ball. They are called fullerenes, although they are more commonly referred to as buckyballs Fullerenes have three covalent bonds to each carbon atom, this leaves delocalised electrons in the structure and the possibility of electrical conductivity. The most stable fullerene involves 60 carbon atoms bonded into an approximately spherical shape that is known as buckminsterfullerene.
tetrahedral
this repulsion between the electron pairs results in a tetrahedral shape. The tetrahedral shape ensures that the electron pairs are as far from each other as possible with angles of 109.5* between all of the single bonds. LONE PAIRS: 0 ANGLE: 109.5 Eg. Methane
relative atomic mass
weighed average of of the relative masses of the isotopes of the element on the carbon 12 scale
why are metals malleable and ductile
when a force causes metal ions to move past each other, layers of ions are still held together by the delocalised electrons between them
polar monomers
when a polymer is made from polar monomers, the chain will be held by strong polar attractions (dipole dipole or hydrogen). When it's made from 2 non polar molecules the intermolecular forces are weak dispersion forces.
when ice melts in water on density
when ice melts and forms liquid water, the density of the water increases rapidly. This is because the open crystal lattice collapses and the water molecules pack together more tightly. However, as the temperature of the water increases further, water molecules in the liquid move and vibrate more rapidly. The movement causes the molecules to spread further apart. As the molecules move further apart, the liquid becomes less dense.
reactivity of metals
when metals react they lose electrons, so its the measure of how easily an atom of a metallic element can lose electrons
reactivity trends explained
when metals react, their atoms tend to form positive ions by donating one or more of their valence electrons to other atoms. The metal atoms that require less energy to remove electrons tend to be most reactive. The most reactive metals tend to be those with the lowest ionisation energy, which are found in the bottom left hand corner of the periodic table
what is the origin of crude oil
when prehistoric marine microorganisms, such as bacteria and plankton, died and were buried by sands millions of years ago, these organisms accumulated as organic sediment and gradually became part of the Earth's crust. Over millions of years, this organic material was affected by high temperatures and pressures, causing the oils and fats to be converted into hydrocarbons. This mixture of hydrocarbons is crude oil. Crude oil has a low density, which means it could migrate upwards through the crust, where it often became trapped beneath impervious (unable to be passed through) rock. Accumulation of oil and gas under the rock creates an oil fields.
polyethene extent of branching (HDPE and LDPE)
when there are few short branches in long chains, the molecules pack together closely and are therefore high density polyethene (HDPE) which have a high percentage of crytallinity and good mechanical properties. When polyethene is made under high pressure conditions, there is a lot of branching, these branches prevent formation of crytalline regions. It's softer and more flexible and has a low percentage of crystallinity
define functional groups
while carbon atoms are covalently bonded only to other carbon and hydrogen atoms in alkanes, alkenes and alkynes, it is possible for carbon to fomr covalent bonds with other atoms or groups of atoms called functional groups. A functional group is an atom or a group of atoms that gives a characteristic set of chemical properties to a molecule containing those atoms . Members of the same homologous series contain the same functional group. The presence of the same functional group in these molecules means that they have similar, although not identical, physical and chemical properties.
