Chemistry IGCSE - topic 1 - principles of chemistry

Avogadro's Law

Avogadro's Law states that at the same conditions of temperature and pressure, equal amounts of gases occupy the same volume of space At room temperature and pressure, the volume occupied by one mole of any gas was found to be 24 dm3 or 24,000 cm3 This is known as the molar gas volume at RTP RTP stands for "room temperature and pressure" and the conditions are 20 ºC and 1 atmosphere (atm)

The Mole

Chemical amounts are measured in moles The symbol for the unit mole is mol One mole of a substance contains the same number of the stated particles, atoms, molecules, or ions as one mole of any other substance The number of atoms, molecules or ions in a mole (1 mol) of a given substance is the Avogadro constant. The value of the Avogadro constant is 6.02 x 1023 per mole For example: One mole of sodium (Na) contains 6.02 x 1023 atoms of sodium One mole of hydrogen (H2) contains 6.02 x 1023 molecules of hydrogen One mole of sodium chloride (NaCl) contains 6.02 x 1023 formula units of sodium chloride

Calculate Reacting Masses Example 1Calculate the mass of magnesium oxide that can be made by completely burning 6.0 g of magnesium in oxygen in the following reaction: 2Mg (s) + O2 (g) ⟶ 2 MgO (s)

Chemical equations can be used to calculate the moles or masses of reactants and products To do this, information given in the question is used to find the amount in moles of the substances being considered Then, the ratio between the substances is identified using the balanced chemical equation Once the moles have been determined they can then be converted into grams using the relative atomic or relative formula masses moles = mass/mr moles = 6/24 = 0.25 2mg:2mgo ratio is 1:1 so 0.25 moles Mg produces 0.25 moles Mgo mass=moles x Mr Mass = 0.25 x 40 = 10g

Anions & Cations

During electrolysis the electrons move from the power supply towards the cathode Electron flow in electrochemistry thus occurs in alphabetical order as electrons flow from the anode to the cathode Positive ions within the electrolyte migrate towards the negatively charged electrode which is the cathode Negative ions within the electrolyte migrate towards the positively charged electrode which is the anode Exam Tip When a metal conducts it is the electrons that are moving through the metal. When a salt solution conducts it is the ions in the solution that move towards the electrodes while carrying the electrons.

Graphite

Each carbon atom in graphite is bonded to three others forming layers of hexagons, leaving one free electron per carbon atom These free electrons migrate along the layers and are free to move and carry charge, hence graphite can conduct electricity The covalent bonds within the layers are very strong, but the layers are attracted to each other by weak intermolecular forces, so the layers can slide over each other making graphite soft and slippery Properties of Graphite Graphite has the following physical properties: It conducts electricity and heat It has a very high melting point It is soft and slippery and less dense than diamond (2.25 g / cm3) The weak intermolecular forces make it a useful material It is used in pencils and as an industrial lubricant, in engines and in locks It is also used to make inert electrodes for electrolysis, which is particularly important in the extraction of metals such as aluminium

Conductivity of Covalent Compounds

Electric current is the flow of charged particles This usually refers to electrons, but it could also mean the flow of ions Collectively, they can be termed freely moving charged particles Most covalent compounds do not conduct electricity as they have no freely moving charged particles to carry the current They act as insulators and have many applications which rely on that property Covalent substances are used as electrical insulators in solid, liquid and gaseous form For example, sulfur hexafluoride is a dense gas used to insulate electrical transformers Silicone oils and liquid hydrocarbons are also used in electrical equipment Common insulators include the plastic coating around household electrical wiring: Covalent compounds are used as insulating materials There are some exceptions to conductivity in covalent compounds Organic polymers have been developed which have multiple adjacent double bonds that allow electrons to migrate along the length of the polymer chains These unusual materials have potential uses as electronic components and biomedical applications

The Structure of the Atom

Elements are made of tiny particles of matter called atoms Each atom is made of subatomic particles called protons, neutrons and electrons Their size is so tiny that we can't really compare their masses in conventional units such as kilograms or grams, so a unit called the relative atomic mass is used One relative atomic mass unit is equal to one twelfth the mass of a carbon-12 atom. All other elements are measured relative to the mass of a carbon-12 atom and since these are ratios, the relative atomic mass has no units Hydrogen for example has a relative atomic mass of 1, meaning that 12 atoms of hydrogen would have exactly the same mass as 1 atom of carbon The relative mass and charge of the subatomic particles are shown below:

Chemical properties of elements in the same group

Elements in the same group in the periodic table will have similar chemical properties This is because they have the same number of outer electrons so will react and bond similarly The group number of an element which is given on the periodic table indicates the number of electrons in the outer shell (valence electrons) This rule holds true for all elements except helium; although is in group 0, it has only one shell, the first and innermost shell, which holds only 2 electrons We can use the group number to predict how elements will react as the number of valence shell electrons in an element influences how the element reacts. Therefore, elements in the same group react similarly By observing the reaction of one element from a group, you can predict how the other elements in that group will react By reacting two or more elements from the same group and observing what happens in those reactions you can make predictions about reactivity and establish trends in reactivity in that group For example, lithium, sodium and potassium are in group 1 and can all react with elements in group 7 to form an ionic compound The group 1 metals become more reactive as you move down the group while the group 7 metals show a decrease in reactivity moving down the group

Nothing created - nothing destroyed

New substances are made during chemical reactions However, the same atoms are always present before and after reaction They have just joined up in different ways Atoms cannot be created or destroyed, so if they exist in the reactants then they absolutely must be in the products! Because of this the total mass of reactants is always equal to the total mass of products This idea is known as the Law of Conservation of Mass

Formation of Covalent Bonds

Non-metal atoms can share electrons with other non-metal atoms to obtain a full outer shell of electrons When atoms share pairs of electrons, they form covalent bonds Covalent bonds between atoms are very strong When two or more atoms are chemically bonded together, they form 'molecules' Covalently bonded substances may consist of small molecules or giant molecules Weak intermolecular forces exist between individual molecules E.g. Each liquid water molecule consists of two hydrogen atoms covalently bonded to an oxygen atom, and in between two individual water molecules there are weak intermolecular forces Shared electrons are called bonding electrons and occur in pairs Electrons on the outer shell which are not involved in the covalent bond(s) are called non-bonding electrons Simple covalent molecules do not conduct electricity as they do not contain free electrons A key difference between covalent bonds and ionic bonds is that in covalent bonds the electrons are shared between the atoms, they are not transferred (donated or gained) and no ions are formed.

Practical: Investigate Paper Chromatography Using Inks & Food Colourings

Objective: Investigate how paper chromatography can be used to separate and identify a mixture of food colourings Hypothesis: Rf values can be used to identify the components of an unknown mixture by comparison with Rfvalues of known substances Materials: A 250 cm3 beaker A wooden spill A rectangle of chromatography paper Four known food colourings labelled A-D An unknown mixture of food colourings labelled U Five glass capillary tubes Paper clip Ruler & pencil Practical Tip: The pencil line must never be below the level of the solvent as the samples will be washed away Method: Use a ruler to draw a horizontal pencil line 2 cm from the end of the chromatography paper Use a different capillary tube to put a tiny spot of each colouring A, B, C and D on the line Use the fifth tube to put a small spot of the unknown mixture U on the line Make sure each spot is no more than 2-3 mm in diameter and label each spot in pencil Pour water into the beaker to a depth of no more than 1 cm and clip the top of the chromatography paper to the wooden spill. The top end is the furthest from the spots Carefully rest the wooden spill on the top edge of the beaker. The bottom edge of the paper should dip into the solvent Allow the solvent to travel undisturbed at least three quarters of the way up the paper Remove the paper and draw another pencil line on the dry part of the paper as close to the wet edge as possible. This is called the solvent front line Measure the distance in mm between the two pencil lines. This is the distance travelled by the water solvent For each of food colour A, B, C and D measure the distance in mm from the start line to the middle of the spot Evaluation: The Rf values of food colours A, B, C and D should be compared to that for the unknown sample as well as a visual comparison being made Conclusion: The use of chromatography and Rf values is a viable method of identifying unknown mixtures given reference material

Deducing Dot & Cross Diagrams for Ionic Compounds

Sodium is a group 1 metal so will lose one outer electron to another atom to gain a full outer shell of electrons A positive sodium ion with the charge 1+ is formed Chlorine is a group 7 non-metal so will need to gain an electron to have a full outer shell of electrons One electron will be transferred from the outer shell of the sodium atom to the outer shell of the chlorine atom A chlorine atom will gain an electron to form a negatively charged chloride ion with a charge of 1-

Solubility Curves

Solubility graphs or curves represent solubility in g per 100 g of water plotted against temperature To plot a solubility curve, the maximum mass of solvent that can be dissolved in 100 g of water before a saturated solution is formed, is determined at a series of different temperatures

tomic Structure Key Terms Table

atomic number - the number of protons in the nucleus of an atom mass number - the sum of the number of protons and neutrons in the nucleus of an atom isotopes - atoms of the same element contain the same number of protons and electrons but a different number of neutrons. therefore, they have the same atomic number but a different mass number relative atomic mass (Ar) - weighted average mass of one atom of an element, taking into account the abundance of all the isotopes of that element. it is measured as a ratio 1/12 of the mass of an atom of carbon -12

Positive ions are called ...... and form when atoms ...... meaning they have .....

cations lose electrons more protons than electrons

Diffusion in gases - Diffusion of red-brown bromine gas

diffusion of red-brown bromine gas Description: Here, we see the diffusion of bromine gas from one gas jar to another After 5 minutes the bromine gas has diffused from the bottom jar to the top jar Explanation: The air and bromine particles are moving randomly and there are large gaps between particles The particles can therefore easily mix together

Classify an Element, Compound or Mixture Table

element - a substance made up of atoms that all contain that same number of protons (one type of atoms) and cannot be split into anything simpler. There are 118 known elements examples: hydrogen, oxygen, carbon compound - A pure substance made up of two or more elements chemically combined together. There are unlimited types of compounds. cannot be separated by physical methods of separation examples; copper (II) sulphate, calcium carbonate Mixture - a combination of two or more substances (elements and/or compounds) that are not chemically joined together. Can be separated by physical methods of separation examples: salt and water, air

The Charges of Common Negative Ions Table

group 5 Non-metals (N, P, As) - 3- group 6 non-metals (O, S, Se) - 2- group 7 non-metals (F, Cl, Br, I, At) - 1- Hydroxide - OH- Carbonate - CO2−3 Nitrate - NO-3 Sulfate - SO2-4

Summary Table of the Physical Properties of Metals

high melting and boiling point - there are many strong metallic bonds in giant metallic structures so large amounts of heart energy are needed to overcome forces and break these bonds good conductors of electricity and heat - metals are good conductors because of the free electrons that are available to move and carry charge. when a metal is used in an electrical circuit, electrons entering one end of the metal cause a delocalised electron to displace it itself from the other end. hence electrons can flow so electricity is conducted malleable and ductile - layers of positive ions can easily slide over one another and take up different positions. This does not disrupt the metallic bonding as the valence electrons so not belong to any particular metal atom and so they can move with the layers of positive ions, maintaining the electrostatic forces. The metallic bonds are thus not broken and as a result, metallic bonds are strong but flexible. Therefore, they can be hammered into different shapes without breaking.

Elements are arranged on the periodic table in order of

increasing atomic number Each element has one proton more than the element preceding it This is done so that elements end up in columns with other elements which have similar properties

A Summary of State Changes

melting - solid to liquid boiling - liquid to a gas (from below surface as well as at surface) freezing - liquid to a solid evaporation - liquid to a gas (at surface only) condensation - gas to a liquid sublimation - solid to a gas

Relationship between Empirical and Molecular Formula

methane EF - CH4 MF - CH4 Ethane EF - CH3 MF - C2H6

All metals lose electrons to other atoms to become .............. All non-metals gain electrons from other atoms to become ..........

positively charged ions negatively charged ions

Characteristic Properties of Metals and Non-Metals

property - metals - non-metals electron arrangement - metals: 1-3 (more in periods 5&6) outer shell electrons - non-metals: 4-7 electrons in the outer shell Bonding - metals: metallic due to loss of outer shell electrons - non-metals: covalent by sharing of outer shell electrons electrical conductivity - metals: good conductors of electricity - non-metals: poor conductors of electricity type of oxide - metals: basic oxides (a few are amphoteric) - non-metals: acidic oxides (some are neutral) reaction with acids - metals: many react with acids - non-metals: do not react with acids physical characteristics - metals: malleable, can be bent and shaped high melting and boiling point - non-metals: flaky, brittle low melting point and boiling point

Atoms & Molecules Definitions Table

Atoms - the smallest particles of an element that consists of electrons surrounding a nucleus that contains protons and neutrons Molecule - A group of two or more atoms chemically joined together forming an identifiable unit which retains the properties and composition of the substance

Expressing Concentr

A solid substance that dissolves in a liquid is called a solute, the liquid is called a solvent and the two when mixed together form a solution Most chemical reactions occur between solutes which are dissolved in solvents, such as water or an organic solvent Concentration simply refers to the amount of solute there is in a specific volume of the solvent The greater the amount of solute in a given volume then the greater the concentration A general formula triangle for concentration is thus: It is useful to a chemist to express concentration in terms of moles per unit volume Concentration can therefore be expressed in moles per decimetre cubed The units in the answer can be written as mol dm-3 or mol/dm3: concentration (mol dm3) = number of moles of solute (mol) / volume of solution (dm3) You may have to convert from g dm-3 into mol dm-3 and vice versa depending on the questionTo go from g dm-3 to mol dm-3:Divide by the molar mass in grams To go from mol dm-3 to g dm-3:Multiply by the molar mass in grams To go from cm3 to dm3 : divide by 1000 To go from dm3 to cm3 : multiply by 1000

Practical: Determine the Formula of Magnesium Oxide

Aim: To determine the empirical formula of magnesium oxide by combustion of magnesium Method: Measure mass of crucible with lid Add sample of magnesium into crucible and measure mass with lid (calculate the mass of the metal by subtracting the mass of empty crucible) Strongly heat the crucible over a Bunsen burner for several minutes Lift the lid frequently to allow sufficient air into the crucible for the magnesium to fully oxidise without letting magnesium oxide smoke escape Continue heating until the mass of crucible remains constant (maximum mass), indicating that the reaction is complete Measure the mass of crucible and contents (calculate the mass of metal oxide by subtracting the mass of empty crucible) Working out the empirical formula: Mass of metal: Subtract mass of crucible from magnesium and the mass of the empty crucible Mass of oxygen: Subtract mass of the magnesium used from the mass of magnesium oxide Step 1 - Divide each of the two masses by the relative atomic masses of the elements Step 2 - Simplify the ratio magnesium oxygen Mass a b Mole a / Ar b / Ar = x = y Ratio x : y Step 3 - Represent the ratio into the form 'MxOy' E.g, MgO

Practical: Determine the Formula of Copper(II)Oxide

Aim: To determine the formula of copper(II)oxide by reduction with methane Method: Measure mass of the empty boiling tube Place metal oxide into a horizontal boiling tube and measure the mass again Support the tube in a horizontal position held by a clamp A steady stream of natural gas(methane) is passed over the copper(II)oxide and the excess gas is burned off The copper(II)oxide is heated strongly using a Bunsen burner Heat until metal oxide completely changes colour, meaning that all the oxygen has been removed Measure mass of the tube remaining metal powder and subtract the mass of the tube Working out empirical formula: Mass of Metal: Measure mass of the remaining metal powder Mass of Oxygen: Subtract mass of the remaining metal powder from the mass of metal oxideStep 1 - Divide each of the two masses by the relative atomic masses of elements Step 2 - Simplify the ratio Metal OxygenMass a b Mole a / Mr b / Mr= x = y Ratio x : y Step 3 - Represent the ratio into the form 'MxOy' E.g, CuO

The Formula of a Hydrated Salt

Aim: To determine the formula of hydrated copper sulfate, CuSO4.xH2ODiagram: Method: Measure mass of evaporating dish Add a known mass of hydrated saltHeat over a Bunsen burner, gently stirring, until the blue salt turns completely white, indicating that all the water has been lostRecord the mass of the evaporating dish and contents Practical tip: Avoid overheating the salt as it could decompose and give you a larger mass change Mass of the white anhydrous salt: Measure mass of white anhydrous salt remaining Mass of water: Subtract mass of the white anhydrous salt remaining from the mass of known hydrated salt Step 1 - Divide the mass of the copper sulfate and the water by their respective molar masses Step 2 - Simplify the ratio of water to copper sulfate anhydrous salt water Mass a b Moles a / Mr b / Mr = y = x Ratio 1 : x Step 3 - Represent the ratio in the form 'salt.xH2O'

Practical: Investigate the Electrolysis of Aqueous Solutions

Aim: To electrolyse aqueous solutions of sodium chloride, sulfuric acid and copper(II)sulfate, and to collect and identify the products at each electrode Method: Add the aqueous solution to a beaker and cover the electrodes with the solution Invert two small test tubes to collect any gaseous products Connect the electrodes to a power pack or battery. Turn on the power pack or battery and allow electrolysis to take place Observations at each electrode are made Gases collected in the test tube can be tested and identified If the gas produced at the cathode burns with a 'pop' when a sample is lit with a lighted splint. This shows that the gas is hydrogen If the gas produced at the anode relights a glowing splint dipped into a sample of the gas. This shows that the gas is oxygen If the anode gas bleaches of a piece of litmus paper this indicates chlorine is the product If a solid forms around the electrode, the metal have been formed. The colour can indicate the metal sodium chloride cathode: colourless gas evolved which goes 'pop' with a lighted splint anode: gas evolved which bleaches litmus paper dilute sulfuric acid cathode: colourless gas evolved which goes 'pop' with a lighted splint Anode: colourless gas evolved which relights a glowing splint Copper (II) sulfate cathode: pink-brown deposit seen on the electrode anode: colourless gas evolved which relights a glowing splint Conclusions: Sodium chloride solutions produces hydrogen at the cathode and chlorine at the anode Dilute sulfuric acid produces hydrogen at the cathode and oxygen at the anode Copper(II)sulfate solution produces copper at the cathode an oxygen at the anode

Practical: Investigate the Solubility of a Solid in Water at a Specific Temperature

Aim: To measure the solubility of a salt at different temperatures Method: Prepare a two beakers, one as a hot water bath and one as an ice bath Using a small measuring cylinder, measure out 4 cm3 of distilled water into a boiling tube. On a balance weigh out 2.6 g of ammonium chloride and add it to the boiling tube Place the boiling tube into the hot water bath and stir until the solid dissolves Transfer the boiling tube to the ice bath and allow it to cool while stirring Note the temperature at which crystals first appear and record it in a table of results Add 1 cm3 of distilled water then warm the solution again to dissolve the crystals Repeat the cooling process again noting the temperature at which crystals first appear. Continue the steps until a total of 10 cm3 of water has been added Graph: Use the results to plot a solubility curve for ammonium chloride at different temperatures. Solubility is on they-axis and temperature is on thex-axisConclusion: The shape of the graph will allow to state how the solubility varies with temperature

Moles-Mass Calculations

Although elements and chemicals react with each other in molar ratios, in the laboratory we use digital balances and grams to measure quantities of chemicals as it is impractical to try and measure out moles Therefore we have to be able to convert between moles and grams We can use the following formula to convert between moles, mass in grams and the molar mass: mass = moles x molar mass

Melting and Boiling Point of Simple Compounds in Relation to Molecular Mass

As the relative molecular mass of a substance increases, the melting and boiling point will increase as well An increase in the relative molecular mass of a substance means that there are more electrons in the structure, so there are more intermolecular forces of attraction that need to be overcome when a substance changes state So larger amounts of heat energy are needed to overcome these forces, causing the compound to have a higher melting and boiling point The family of organic molecules called alkanes show a clear increase in boiling point as the size of the molecule increases

Representing reactions as equations

Chemical equations use the chemical symbols of each reactant and product When balancing equations, there has to be the same number of atoms of each element on either side of the equation in accordance with the Law of Conservation of Mass A symbol equation uses the formulae of the reactants and products to show what happens in a chemical reaction A symbol equation must be balanced to give the correct ratio of reactants and products: S + O2 → SO2 This equation shows that one atom of sulfur (S) reacts with one molecule of oxygen (O2) to make one molecule of sulfur dioxide (SO2) The following non-metals must be written as molecules: H2, N2, O2, F2, Cl2, Br2 and I2 To balance an equation you work across the equation from left to right, checking one element after another If there is a group of atoms, for example a nitrate group (NO3-) that has not changed from one side to the other, then count the whole group as one entity rather than counting the individual atoms Examples of chemical equations: Acid-base neutralisation reaction: NaOH (aq) + HCl (aq) ⟶ NaCl (aq) + H2O (l) Redox reaction: 2Fe2O3 (aq) + 3C (s) ⟶ 4Fe (s) + 3CO2 (g) In each equation there are equal numbers of each atom on either side of the reaction arrow so the equations are balanced

Giant Covalent Structures

Covalent bonding can be responsible for substances that have many different structures and therefore different physical properties We have already seen how small molecules such as H2O and N2 are simple units made from covalently bonded atoms These simple molecules contain fixed numbers of atoms Giant covalent structures on the other hand have a huge number of non-metal atoms bonded to other non-metal atoms via strong covalent bonds These structures can also be called giant lattices and have a fixed ratio of atoms in the overall structure Three common macromolecules you should know about are diamond, graphite and C60 fullerene Giant covalent structures can also be called macromolecules.

Covalent Bonds: Dot & Cross Diagrams

Covalent substances tend to have small molecular structures, such as Cl2, H2O or CO2 These small molecules are known as simple molecules Small covalent molecules can be represented by dot and cross diagrams You need to be able to describe and draw the structures of the following molecules using dot-and-cross diagrams: hydrogen (H2), chlorine (Cl2), oxygen (O2), nitrogen (N2), hydrogen chloride (HCl), water (H2O), ammonia (NH3) and methane (CH4) The correct dot and cross diagrams for these molecules are shown below:

Dissolving potassium manganate (VII) in water

Description: When potassium magnate (VII) crystals are dissolved in water, the solution can be diluted several times The colour fades but does not disappear until a lot of dilutions have been done Explanation: This indicates that there are a lot of particles in a small amount of potassium manganate (VII) and therefore the particles must be very small

Diamond

Diamond and graphite are allotropes of carbon Both substances contain only carbon atoms but due to the differences in bonding arrangements they are physically completely different In diamond, each carbon atom bonds with four other carbons, forming a tetrahedron All the covalent bonds are identical, very strong and there are no intermolecular forces Properties of Diamond Diamond has the following physical properties: It does not conduct electricity It has a very high melting point It is extremely hard and has a density of 3.51 g / cm3 - a little higher than that of aluminium All the outer shell electrons in carbon are held in the four covalent bonds around each carbon atom, so there are no freely moving charged particles to the current The four covalent bonds are very strong and extend in a giant lattice, so a very large amount of heat energy is needed to break the lattice Diamond ́s hardness makes it very useful for purposes where extremely tough material is required Diamond is used in jewellery and for coating blades in cutting tools The cutting edges of discs used to cut bricks and concrete are tipped with diamonds Heavy-duty drill bits and tooling equipment are also diamond tipped Exam Tip Diamond is the hardest naturally occurring mineral, but it is by no means the strongest. Students often confuse hard with strong, thinking it is the opposites of weak. Diamonds are hard, but brittle - that is, they can be smashed fairly easily with a hammer. The opposite of saying a material is hard is to describe it as soft.

Empirical formula:

Empirical formula: gives the simplest whole number ratio of atoms of each element in the compound It is calculated from knowledge of the ratio of masses of each element in the compound Example: A compound that contains 10 g of hydrogen and 80 g of oxygen has an empirical formula of H2O. This can be shown by the following calculations: Amount of hydrogen atoms = mass in grams ÷ Arof hydrogen = (10 ÷ 1) =10 molesAmount of oxygen atoms = mass in grams ÷ Arof oxygen = (80 ÷ 16) =5 moles Since equal numbers of moles of atoms contain the same number of atoms, the ratio of hydrogen atoms to oxygen atoms is 2:1 Hence the empirical formula is H2O Molecular formula: gives the exact numbers of atoms of each element present in the formula of the compound Divide the relative formula mass of the molecular formula by the relative formula mass of the empirical formula Multiply the number of each element present in the empirical formula by this number to find the molecular formula

How to deduce the charge of an ion

Find the number of electrons in the outer electron shell Find out if it is easy for the atom to gain electron or to donate electron (in most cases atoms that have fewer than four electrons, donate electrons and atoms that have more than 4 electrons, receive electrons) Atoms that gain electrons become negative ions and atoms that donate electron forms positive ion You also need to learn the formula of compound ions, that is, ions made from more than one element

Conductivity & Ionic Compounds

For electrical current to flow there must be present freely moving charged particles such as electrons or ions Ionic compounds can conduct electricity in the molten state or in solution as they have ions that can move and carry charge They cannot conduct electricity in the solid state as the ions are in fixed positions within the lattice and are unable to move Molten or aqueous particles move and conduct electricity but cannot in the solid state

Formulae for Ionic Compounds

For ionic compounds you have to balance the charge of each part by multiplying each ion until the sum of the charges = 0 Example: what is the formula of aluminium sulfate?Write out the formulae of each ion, including their chargesAl3+ SO42- Balance the charges by multiplying them out: Al3+ x 2 = +6 and SO42- x 3 = -6; so +6 - 6 = 0 So the formula is Al2(SO4)3

C60 fullerene

Fullerenes are a group of carbon allotropes which consist of molecules that form hollow tubes or spheres Fullerenes can be used to trap other molecules by forming around the target molecule and capturing it, making them useful for targeted drug delivery systems They also have a huge surface area and are useful for trapping catalyst molecules onto their surfaces making them easily accessible to reactants so catalysis can take place Some fullerenes are excellent lubricants and are starting to be used in many industrial processes The first fullerene to be discovered was buckminsterfullerene which is affectionately referred to as a "buckyball" In this fullerene, 60 carbon atoms are joined together forming 20 hexagons and 12 pentagons which produce a hollow sphere that is the exact shape of a soccer ball

The Charges of Common Positive Ions Table

Group 1 metals (li, Na, K, Rb, Cs, Fr) - 1+ Group 2 metals (Be, Mg, Ca, Sr, Ba, Ra) - 2+ Group 3 metals (Al, Ga, In, Ti) - 3+ silver - Ag+ Copper (II) - Cu 2+ Iron (II) - Fe 2+ Iron (III) - Fe 3+ Lead - Pd 2+ Zinc - Zn 2+ Hydrogen - H+ Ammonium -NH4+

Balancing Equations using Reacting Masses

If the masses of reactants and products of a reaction are known then we can use them to write a balanced equation for that reaction This is done by converting the masses to moles and simplifying to find the molar ratios

Writing Half-Equations

In electrochemistry we are mostly concerned with the transfer of electrons, hence the definitions of oxidation and reduction are applied in terms of electron loss or gain rather than the addition or removal of oxygen Oxidation is when a substance loses electrons and reduction is when a substance gains electrons As the ions come into contact with the electrode, electrons are either lost or gained and they form neutral substances These are then discharged as products at the electrodes At the anode, negatively charged ions lose electrons and are thus oxidised At the cathode, the positively charged ions gain electrons and are thus reduced This can be illustrated using half equations which describe the movement of electrons at each electrode Electrolysis of molten lead(II) bromide In the electrolysis of molten lead(II) bromide the half equation at the negative electrode (cathode) is: Pb2+ + 2e- ⟶ Pb Reduction At the positive electrode (anode) bromine gas is produced by the discharge of bromide ions: 2Br- - 2e- ⟶ Br2 Oxidation or 2Br- ⟶ Br2 + 2e- Exam Tip At the anode, it doesn't matter whether you subtract the electrons on the left or add them on the right. Most chemists prefer to add them on the right, because chemical equations, by convention, generally involve the addition of materials rather than the subtraction.

Pure Substance vs Mixture

In everyday language we use the word pure to describe when something is natural or clean and to which nothing else has been added In chemistry a pure substance may consist of a single element or compound which contains no other substances For example a beaker of a sample of pure water contains only H2O molecules and nothing else If salt were added to the beaker then a mixture is produced A mixture consists of two or more elements or compounds that are physically mixed together, they are not chemically combined The chemical properties of the substances in a mixture remain unchanged Substances in mixtures can be separated by physical means Air for example is a mixture of nitrogen, oxygen and some other gases such as carbon dioxide and argon

Electrolysis of aqueous sodium chloride In the electrolysis of aqueous sodium chloride the half equation at the negative electrode (cathode) is:

In the electrolysis of aqueous sodium chloride the half equation at the negative electrode (cathode) is: 2H+ + 2e- ⟶ H2 Reduction At the positive electrode (anode) chlorine gas is produced by the discharge of chloride ions: 2Cl- - 2e- ⟶ Cl2 Oxidation or 2Cl- ⟶ Cl2 + 2e-

Giant Ionic Lattices

Ionic compounds are made of charged particles called ions which form a giant lattice structure Ionic substances have high melting and boiling points due to the presence of strong electrostatic forces acting between the oppositely charged ions These forces act in all directions and a lot of energy is required to overcome them Strong electrostatic forces act in all directions in an ionic solid such as sodium chloride Ionic compounds are usually solid at room temperature and are non-volatile They are usually water soluble as both ionic compounds and water are polar substances Ionic compounds are soluble in water because the ions are easily hydrated by polar water molecules Ions with higher charge have stronger electrostatic forces and will thus have higher melting and boiling points.

Conductivity of Ionic Compounds

Ionic compounds can conduct electricity in the molten state or in solution as they have ions that can move and carry charge They cannot conduct electricity in the solid state as the ions are in fixed positions within the lattice and are unable to move Molten or aqueous particles move and conduct electricity but cannot in solid form

Electrolysis of Molten Compounds

Lead(II) bromide is a binary ionic compound meaning that it is a compound consisting of just two elements joined together by ionic bonding When these compounds are heated beyond their melting point, they become molten and can conduct electricity as their ions can move freely and carry the charge These compounds undergo electrolysis and always produce their corresponding element To predict the products of any binary molten compound first identify the ions present The positive ion will migrate towards the cathode and the negative ion will migrate towards the anode Therefore the cathode product will always be the metal and the product formed at the anode will always be the non-metal Method: Add lead(II) bromide into a crucible and heat so it will turn molten, allowing ions to be free to move and conduct an electric charge Add two graphite rods as the electrodes and connect this to a power pack or battery Turn on the power pack or battery and allow electrolysis to take place Negative bromide ions move to the positive electrode (anode) and lose two electrons to form bromine molecules. There is bubbling at the anode as brown bromine gas is given off Positive lead ions move to the negative electrode (cathode) and gain electrons to form grey lead metal which deposits on the bottom of the electrode Electrode Products: Anode: Bromine gas Cathode: Lead metal Exam Tip Remember electrodes need to be inert such as graphite or platinum so that they don't participate in a side reaction with the electrolyte.

Magnesium Oxide Dot & Cross Diagram

Magnesium is a group 2 metal so will lose two outer electrons to another atom to have a full outer shell of electrons A positive ion with the charge 2+ is formed Oxygen is a group 6 non-metal so will need to gain two electrons to have a full outer shell of electrons Two electrons will be transferred from the outer shell of the magnesium atom to the outer shell of the oxygen atom Oxygen atom will gain two electrons to form a negative ion with charge 2- MgO

A Summary of State Changes - detail

Melting Melting is when a solid changes into a liquid The process requires heat energy which transforms into kinetic energy, allowing the particles to move It occurs at a specific temperature known as the melting point which is unique to each pure solid Boiling Boiling is when a liquid changes into a gas This requires heat which causes bubbles of gas to form below the surface of a liquid, allowing for liquid particles to escape from the surface and from within the liquid It occurs at a specific temperature known as the boiling point which is unique to each pure liquid Freezing Freezing is when a liquid changes into a solid This is the reverse of melting and occurs at exactly the same temperature as melting, hence the melting point and freezing point of a pure substance are the sameWater for example freezes and melts at 0 ºC It requires a significant decrease in temperature (or loss of thermal energy) and occurs at a specific temperature which is unique for each pure substance Evaporation When a liquid changes into a gas Evaporation occurs only at the surface of liquids where high energy particles can escape from the liquids surface at low temperatures, below the boiling point of the liquid The larger the surface area and the warmer the liquid/surface, the more quickly a liquid can evaporate Evaporation occurs over a range of temperatures, but heating will speed up the process as particles need energy to escape from the surface Condensation When a gas changes into a liquid, usually on cooling When a gas is cooled its particles lose energy and when they bump into each other, they lack energy to bounce away again, instead grouping together to form a liquid Sublimation When a solid changes directly into a gas This happens to only a few solids, such as iodine or solid carbon dioxide The reverse reaction also happens and is called desublimation or deposition

Metallic Bonding

Metal atoms are held together strongly by metallic bonding Within the metal lattice, the atoms lose their valence electrons and become positively charged The valence electrons no longer belong to any metal atom and are said to be delocalised They move freely between the positive metal ions like a sea of electrons Metallic bonds are strong and are a result of the attraction between the positive metal ions and the negatively charged delocalised electrons The properties of metals can be modified, sometimes significantly, by mixing it with another metal or non-metal to create and alloy

The link between metallic bonding and the properties of metals

Metals have high melting and boiling points There are many strong metallic bonds in giant metallic structures A lot of heat energy is needed to overcome forces and break these bonds Metals conduct electricity There are free electrons available to move and carry charge Electrons entering one end of the metal cause a delocalised electron to displace itself from the other end Hence electrons can flow so electricity is conducted Metals are malleable and ductile Layers of positive ions can slide over one another and take up different positions Metallic bonding is not disrupted as the valence electrons do not belong to any particular metal atom so the delocalised electrons will move with them Metallic bonds are thus not broken and as a result metals are strong but flexible They can be hammered and bent into different shapes without breaking

Negative ions are called ..... and form when atoms ......... meaning they have .......

anions gain electrons more electrons than protons

Linking the Mole and the Atomic mass

One mole of any element is equal to the relative atomic mass of that element in grams or for a compound the relative formula mass in grams This is called the molar mass If you had 6.02 x 1023 atoms of carbon in your hand, that number of carbon atoms would have a mass of 12 g (because the Ar of carbon is 12) So one mole of helium atoms would have a mass of 4 g (Ar of He is 4), one mole of lithium would have a mass of 7 g (Ar of Li is 7) and so on To find the mass of one mole of a compound, we add up the relative atomic masses So one mole of water would have a mass of (2 x 1) + 16 = 18 g So one carbon atom has the same mass as 12 hydrogen atoms

The table is arranged in vertical columns called groups and in rows called periods

Period: These are the horizontal rows that show the number of shells of electrons an atom has and are numbered from 1 - 7 E.g. elements in period 2 have two electron shells, elements in period 3 have three electron shells

The Mass & Charge of Subatomic Particles Table

Proton relative mass - 1 charge - +1 neutron relative mass - 1 charge - 0 electron relative mass - 1/1840 charge - -1

Distinguishing Purity

Pure substances melt and boil at specific and sharp temperatures e.g. pure water has a boiling point of 100 °C and a melting point of 0 °C Mixtures have a range of melting and boiling points as they consist of different substances that tend to lower the melting point and broaden the melting point range Melting and boiling points data can therefore be used to distinguish pure substances from mixtures Melting point analysis is routinely used to assess the purity of drugs This is done using a melting point apparatus which allows you to slowly heat up a small amount of the sample, making it easier to observe the exact melting point This is then compared to data tables The closer the measured value is to the actual melting or boiling point then the purer the sample is

Identifying Mixtures

Pure substances will produce only one spot on the chromatogram If two or more substances are the same, they will produce identical chromatograms If the substance is a mixture, it will separate on the paper to show all the different components as separate spots An impure substance therefore will produce a chromatogram with more than one spot

Electrolysis of Aqueous Solutions

Rules: Aqueous solutions will always have water present Some water molecules split up into hydrogen and hydroxide ions, H+ and OH-, which participate in the electrolysis reactions Positive Electrode OH- ions and non-metal ions are attracted to the positive electrode Either OH- or non-metal ions will lose electrons and oxygen gas or a non-metal is released e.g. chlorine The product formed depends on which ion loses electrons more readily Negative Electrode H+ ions and metal ions are attracted to the negative electrode but only one will gain electrons Either hydrogen or a metal will be produced If the metal is above hydrogen in reactivity series, hydrogen will be produced - bubbling will be seen at the cathode The apparatus can be modified for the collection of gases by using inverted test tubes over the electrodes The electrodes are made from graphite which is inert and does not interfere with the electrolysis reactions Exam Tip Once you have identified the ions, the next step is to decide towards which electrode will they be drawn and identify the product formed. It helps if you recall the reactivity series.

Exam Tip - Simple covalent molecules

Simple covalent molecules are small and can be separated into individual molecular units without breaking any chemical bonds (although there will still be strong covalent bonds holding the atoms in each individual molecule together) Giant ionic and covalent structures form huge continuous networks of atoms that are bonded together and cannot be separated into individual units without breaking bonds.

Simple Molecular Structures

Simple molecular structures have covalent bonds joining the atoms together, but intermolecular forces that act between neighbouring molecules They have low melting and boiling points as there are only weak intermolecular forces acting between the molecules These forces are very weak when compared to the covalent bonds and so most small molecules are either gases or liquids at room temperature Often the liquids are volatile As the molecules increase in size the intermolecular forces also increase as there are more electrons available This causes the melting and boiling points to increase Covalent bonds are strong but intermolecular forces are weak The atoms within covalent molecules are held together by covalent bonds while the molecules in a covalent substance are attracted to each other by intermolecular forces.

Solubility Solubility of gases is affected by temperature and pressure; in general:

Solubility is a measurement of how much of a substance will dissolve in a given volume of a liquidThe liquid is called the solventThe solubility of a gas depends on pressure and temperature Different substances have different solubilities Solubility can be expressed in g per 100 g of solvent Solubility of solids is affected by temperature As temperature increases, solids usually become more soluble Solubility of gases is affected by temperature and pressure; in general: As pressure increases, gases become more soluble As temperature increases, gases become less soluble

The empirical formula of X is C4H10S1 and the relative formula mass of X is 180. What is the molecular formula of X? Relative atomic masses: carbon : 12 hydrogen : 1 sulfur : 32

Step 1 - Calculate the relative formula mass of the empirical formula (C x 4) + (H x 10) + (S x 1) = (12 x 4) + (1 x 10) + (32 x 1) = 90 Step 2 - Divide the relative formula mass of X by the mass of the empirical formula 180 / 90 = 2 Step 3 - Multiply each number of elements by 2 (C4 x 2) + (H10 x 2) + (S1 x 2) = (C8) + (H20) + (S2) Molecular Formula of X = C8H20S2

Conservation of Mass

The Law of Conservation of Mass enables us to balance chemical equations, since no atoms can be lost or created You should be able to: Write word equations for reactions outlined in these notes Write formulae and balanced chemical equations for the reactions in these notes

Actual & Theoretical Yield

The actual yield is the recorded amount of product obtained The theoretical yield is the amount of product that would be obtained under perfect practical and chemical conditions It is calculated from the balanced equation and the reacting masses The percentage yield compares the actual yield to the theoretical yield For economic reasons, the objective of every chemical producing company is to have as high a percentage yield as possible to increase profits and reduce costs and waste

Interconversion Between the States of Matter

The amount of energy needed to change state from solid to liquid and from liquid to gas depends on the strength of the forces between the particles The stronger the forces of attraction, the more energy that is needed to overcome them for a state change to occur Therefore, the stronger the forces between the particles the higher the melting point and boiling point of the substance When matter changes from one state to another due to changes in temperature or pressure, the change is called an interconversion of state It is a physical change involving changes in the forces between the particles of the substances, the particles themselves remain the same, as do the chemical properties of the substance Physical changes are relatively easy to reverse as no new substance is formed during interconversions of state The interconversions have specific terms to describe them:

Electronic configuration:

The arrangement of electrons into shells for an atom (e.g. electronic configuration of carbon is 2 . 4)

Why Noble Gases are Unreactive

The elements in group 0 of the periodic table are called the noble gases They are all non-metal, monatomic (exist as single atoms), colourless, non-flammable gases at room temperature The group 0 elements all have full outer shells of electrons; this electronic configuration is extremely stable Elements participate in reactions to complete their outer shells by losing, gaining, or sharing electrons The Group 0 elements do not need to do this, because of their full outer shells which makes them unreactive and inert Other than helium which has 2 electrons in its outer shell, the noble gases have eight valence electrons (which is why you may see this group labelled "group 8") Electronic configurations of the Noble gases: He = 2 Ne = 2, 8 Ar = 2, 8, 8 Kr = 2, 8, 18, 8 Xe = 2, 8, 18, 18, 8

Making Careful Quantitative Measurements

The formulae of simple compounds can be found by careful experimentation and accurate measurements of mass changes The principle is to use mass measurements before and after reaction and then convert masses into moles Using the moles of reactants and products it is possible to deduce molar ratios and hence an empirical formula Experiments which are easier to do using this process involve gases being lost or gained In this example a hydrated salt is heated to drive off the water as water vapour

Cooling Curves

The influence of impurities can be more clearly seen on a heating / cooling curve If the temperature of a liquid is measured as it cools and freezes the data can be used to produce a graph The following graph shows the cooling curve for a sample of a compound The horizontal part of the graph shows that the compound has a sharp melting point, so the compound is pure An impure sample of the compound would produce a gradual decrease in temperature as it freezes as shown in the graph below

Group

The last notation, which is 7, shows that a chlorine atom has 7 outer electrons matching group 7 of the periodic table

Empirical & Molecular Formulae

The molecular formula is the formula that shows the number and type of each atom in a moleculeE.g. the molecular formula of ethanoic acid is C2H4O2 The empirical formula is the simplest whole number ratio of the atoms of each element present in one molecule or formula unit of the compoundE.g. the empirical formula of ethanoic acid is CH2O Organic molecules often have different empirical and molecular formulae The formula of an ionic compound is always an empirical formula

Electronic configuration and position in periodic table

The number of notations in the electronic configuration will show the number of shells of electrons the atom has, showing the period The last notation shows the number of outer electrons the atom has, showing the group

Calculating percentage by mass of an element in a compound

The percentage by mass of an element in a compound can be calculated using the following equation: % mass of an element = Ar x number of atoms of the element / Mr of the compound x 100

Percentage Yield

The percentage yield is a good way of measuring how successful a chemical process is There are often several methods of creating a compound and each method is called a reaction pathway Reaction pathways consist of a sequence of reactions which must occur to produce the required product Companies often investigate and try out different reaction pathways and these are then compared and evaluated so that a manufacturing process can be chosen The percentage yield of each pathway is a significant factor in this decision making process The equation to calculate the percentage yield is percentage yield = actual yield / theoretical yield x 100

Ionic bonding

The positive and negative charges are held together by the strong electrostatic forces of attraction between oppositely charged ions This is what holds ionic compounds together electrostatic forces hold the ions together in sodium chloride

Period:

The red numbers below the electronic configuration show the number of notations which is 3, showing that a chlorine atom has 3 shells of electrons

Calculate Relative Atomic Mass

The relative atomic mass of each element is calculated from the mass number and relative abundances of all the isotopes of a particular element The steps below are to calculate the relative atomic mass Start by finding out the mass of 100 atoms, then divide the result by 100 to get the Ar The top line of the equation can be extended to include the number of different isotopes of a particular element present, so, if there were 3 isotopes present then the top line of the equation would read: ( mass of isotope 1 x % of isotope 1 ) + ( mass of isotope 2 x % of isotope 2 ) / 100

The Three States of Matter

The three states of matter are solids, liquids and gases A substance can usually exist in all three states, dependent on temperature (and pressure) Different state changes occur at the melting point and at the boiling point depending on whether the substance is heating up or cooling down At the melting point Melting (solid → liquid) when heating up Freezing (liquid → solid) when cooling down At the boiling point Boiling (liquid → gas) when heating up Condensing (gas → liquid) when cooling down Individual atoms themselves do not share the same properties as bulk matter The three states of matter can be represented by a simple modelIn this model, the particles are represented by small solid spheres

Electrostatic Attractions

There is a strong electrostatic attraction between the shared pair of electrons and the nuclei of the atoms involved, since the electrons are negatively charged and the nuclei are positively charged The attraction between the shared pair of electrons and the nuclei of the atoms involved in a covalent bond In a normal covalent bond, each atom provide one of the electrons in the bond. A covalent bond is represented by a short straight line between the two atoms, H-H Covalent bonds should not be regarded as shared electron pairs in a fixed position; the electrons are in a state of constant motion and are best regarded as charge clouds Sharing electrons in the covalent bond allows each of the 2 atoms to achieve an electron configuration similar to a noble gas This makes each atom more stable

Group:

These are the vertical columns that show how many outer electrons each atom has and are numbered from 1 - 7, with a final group called group 0 (instead of group 8) E.g. group 4 elements have atoms with 4 electrons in the outermost shell, group 6 elements have atoms with 6 electrons in the outermost shell and so on

Word Equations

These show the reactants and products of a chemical reaction using their full chemical names The reactants are those substances on the left-hand side of the arrow and can be thought of as the chemical ingredients of the reaction They react with each other and form new substances The products are the new substances which are on the right-hand side of the arrow The arrow (which is spoken as "goes to" or "produces") implies the conversion of reactants into products Reaction conditions or the name of a catalyst (a substance added to make a reaction go faster) can be written above the arrow An example is the reaction of sodium hydroxide (a base) and hydrochloric acid produces sodium chloride (common table salt) and water: sodium hydroxide + hydrochloric acid ⟶ sodium chloride + water

Rf Values

These values are used to identify the components of mixtures The Rf value of a particular compound is always the same but it is dependent, however, on the solvent used If the solvent is changed then the value changes Calculating the Rf value allows chemists to identify unknown substances because it can be compared with Rf values of known substances under the same conditions These values are known as reference values Calculation The Retention factor is found using the following calculation: Rf = distance travelled by substance ÷ distance travelled by solvent The Rf value will always lie between 0 and 1; the closer it is to 1, the more soluble is that component in the solvent The Rf value is a ratio and therefore has no units

Conductivity & Covalent Compounds

They are poor conductors of electricity as there are no free ions or electrons to carry the charge Most covalent compounds do not conduct at all in the solid state and are thus insulators Common insulators include the plastic coating around household electrical wiring, rubber and wood The plastic coating around electrical wires is made from covalent substances that do not allow a flow of charge Exam Tip When a covalent molecule melts or boils the covalent bonds do not break, only the intermolecular forces. If you think about it, when you boil a kettle full of water you are not generating large volumes of hydrogen and oxygen gas in your kitchen - this might give you an interesting unwanted chemical reaction ! Boom !

Simple Distillation

This is used to separate a liquid and soluble solid from a solution (e.g., water from a solution of salt water) or a pure liquid from a mixture of liquids The solution is heated, and pure water evaporates producing a vapour which rises through the neck of the round bottomed flask The vapour passes through the condenser, where it cools and condenses, turning into the pure liquid that is collected in a beaker After all the water is evaporated from the solution, only the solid solute will be left behind

Fractional Distillation

This is used to separate two or more liquids that are miscible with one another (e.g., ethanol and water from a mixture of the two) The solution is heated to the temperature of the substance with the lowest boiling point This substance will rise and evaporate first, and vapours will pass through a condenser, where they cool and condense, turning into a liquid that will be collected in a beaker All of the substance is evaporated and collected, leaving behind the other components(s) of the mixture For water and ethanol Ethanol has a boiling point of 78 ºC and water of 100 ºC The mixture is heated until it reaches 78 ºC, at which point the ethanol boils and distills out of the mixture and condenses into the beaker When the temperature starts to increase to 100 ºC heating should be stopped. Water and ethanol are now separated

Paper Chromatography

This technique is used to separate substances that have different solubilities in a given solvent (e.g., different coloured inks that have been mixed to make black ink) A pencil line is drawn on chromatography paper and spots of the sample are placed on it. Pencil is used for this as ink would run into the chromatogram along with the samples The paper is then lowered into the solvent container, making sure that the pencil line sits above the level of the solvent, so the samples don't wash into the solvent container The paper is called the stationary phase The solvent travels up the paper by capillary action, taking some of the coloured substances with it; it is called the mobile phase Different substances have different solubilities so will travel at different rates, causing the substances to spread apartThose substances with higher solubility will travel further than the others This will show the different components of the ink / dye If two or more substances are the same, they will produce identical chromatograms If the substance is a mixture, it will separate on the paper to show all the different components as separate spots An impure substance will show up with more than one spot, a pure substance should only show up with one spot

Crystallisation

Used to separate a dissolved solid from a solution, when the solid is much more soluble in hot solvent than in cold (e.g., copper sulphate from a solution of copper (II) sulphate in water) The solution is heated, allowing the solvent to evaporate, leaving a saturated solution behind Test if the solution is saturated by dipping a clean, dry, cold glass rod into the solutionIf the solution is saturated, crystals will form on the glass rod The saturated solution is allowed to cool slowly Crystals begin to grow as solids will come out of solution due to decreasing solubility The crystals are collected by filtering the solution, they are washed with cold distilled water to remove impurities and are then allowed to dry

Filtration

Used to separate an undissolved solid from a mixture of the solid and a liquid / solution ( e.g., sand from a mixture of sand and water) Centrifugation can also be used for this mixture A piece of filter paper is placed in a filter funnel above a beaker A mixture of insoluble solid and liquid is poured into the filter funnel The filter paper will only allow small liquid particles to pass through as filtrate Solid particles are too large to pass through the filter paper so will stay behind as a residue

To find the volume

Volume (cm3) = Moles x Molar Volume (24dm3/mol or 24000cm3 mol) If the volume is given in cm3 instead of dm3, then divide by 24,000 instead of 24:

Deducing Electronic Configurations

We can represent the electronic structure of atoms using electron shell diagrams Electrons orbit the nucleus in shells and each shell has a different amount of energy associated with it The further away from the nucleus, the more energy a shell has Electrons first occupy the shell closest to the nucleus which can hold a maximum of 2 electrons When a shell becomes full of electrons, additional electrons have to be added to the next shell The second shell and third shell can hold 8 electrons each The outermost shell of an atom is called the valence shell and an atom is much more stable if it can manage to completely fill this shell with electrons In most atoms, the outermost shell is not full and therefore these atoms react with other atoms in order to achieve a full outer shell of electrons (which would make them more stable) In some cases, atoms lose electrons to entirely empty this shell so that the next shell below becomes a (full) outer shell

Relative Formula Mass

We have seen previously that the symbol for the relative atomic mass is Ar This is calculated from the mass number and relative abundances of all the isotopes of a particular element The symbol for the relative formula mass is Mr and it refers to the total mass of the substance If the substance is molecular you can use the term relative molecular mass, but this term should not be used for ionic compounds such as sodium chloride To calculate the Mr of a substance, you have to add up the relative atomic masses of all the atoms present in the formula In accordance with the Law of Conservation of Mass, the sum of the relative formula masses of the reactants will be the same as the sum of the relative formula masses of the products

Calculate Percentage Yield

Yield is the term used to describe the amount of product you get from a reaction In practice, you never get 100% yield in a chemical process for several reasons These include:S ome reactants may be left behind in the equipment The reaction may be reversible and in these reactions a high yield is never possible as the products are continually turning back into the reactantsSome products may also be lost during separation and purification stages such as filtration or distillationThere may be side reactions occurring where a substance reacts with a gas in the air or an impurity in one of the reactantsProducts can also be lost during transfer from one container to another

Diffusion in liquids - Diffusion of potassium manganate(VII) in water over time

after 15 min - potassium manganate molecules diffuse through the solution, from a region of high concentration to a region of low concentration after 4 hours - potassium manganate (VII) solution after 4 hours - equilibrium is reached - concentration of particles now evenly spread through the solution Description: When potassium manganate (VII) crystals are dissolved in water, a purple solution is formed A small number of crystals produce a highly intense colour Explanation: The water and potassium manganate (VII) particles are moving randomly and the particles can slide over each other The particles can therefore easily mix together Diffusion in liquids is slower than in gases because the particles in a liquid are closely packed together and move more slowly

Summary of the Properties of Solids, Liquids and Gases

solid arrangment of particles - regular arrangement movement of particles - vibrate about a fixed position closeness of particles - very close Liquid arrangment of particles - randomly arranged movement of particles - move around each other closeness of particles - close Gas arrangement of particles - randomly arranged movement of particles - move quickly in all directions closeness of particles - far apart

Terminology About Solutions Table

solvent Meaning: the liquid in which a solute dissolves Example: the water in sea water - solute Meaning: the substance which dissolves in a liquid to from a solution Example: the salt in seawater - solution Meaning: the mixture formed when a solute is dissolved in a solvent Example: seawater - saturated solution Meaning: a solution which the maximum concentration of solute dissolved in the solvent Example: seawater in the dead sea - soluble Meaning: describes a substance that will dissolve Example: salt is soluble in water - insoluble Meaning: describes a substance that wont dissolve Example: sand is insoluble in water

An ion is an electrically charged atom or group of atoms formed by

the loss or gain of electrons This loss or gain of electrons takes place to obtain a full outer shell of electrons The electronic structure of ions of elements in groups 1, 2, 3, 5, 6 and 7 will be the same as that of a noble gas - such as helium, neon, and argon