Science Grade 8: Final Exam

Group number

(how many and what are they used for?) Atoms of elements in the same group(family), or column (p.114) have the same number of valence electrons 18 groups

Periods

(how many and what do they tell us?) refer to your periodic table 7 Periods (p.114) horizontal rows of elements

Balancing equations

(know how, but remember-it's all multiple choice) When the number of atoms of each element on the right-hand side of the equations matches the number of atoms of each element on the left, then the chemical equations is said to be balanced. Follows the Law of Conservation of Mass. An equation can be balanced only by putting numbers, called coefficients, in front of the chemical formulas.(p.199) You cannot change the subscripts.

Density

= Mass/Volume (be able to find volume and mass using this formula as well) Density equation: D = m/V (p.48) Density is a physical property. If an object has less density than water, it will float. If an object has more density than water, it will sink.

Chemical formula

A chemical formula represents compounds and molecules. (p.41) Example: table sugar 3C12H22O11 indigo ___C16H10N2O2___ rust ____Fe2O3___ Subscript: The number of atoms of each element is written after the element's symbol.(The little number) ( p.41) Coefficients are the numbers in front of the formula.

Endothermic Reaction

A chemical reaction that ABSORBS energy in the form of heat

Exothermic Reaction

A chemical reaction that RELEASES energy in the form of heat

Surface area

A large surface area speeds up reactions.(p.206) Massive, bulky molecules react slower.(p.207) Example:If you change the surface area of a potato by cutting it up, it will cook faster. This is because solids that have a large surface area react more rapidly because more particles can come in contact with the other reactants.

colloid

A mixture containing small, undissolved particles that do not settle out.

Heterogeneous mixture

A mixture in which different materials can be distinguished easily example: fruit salad; compare 2 shovels ful of dirt from a garden-won't be the same

suspension

A mixture in which particles can be seen and easily separated by settling or filtration

Decomposition

Digestion, "cracking" oil, electrolysis (water breaks down into hydrogen gas and oxygen gas when an electric current flows through the water(p.191) a reaction is broken apart AB → A + B

Gas

Evaporation is the change of a substance from a liquid to a gas. (p.75)

negative ion, or anion.

Gaining an electron forms a

Noble gases

Group 18 inert/unreactive are single atoms orbitals are full of electrons, so don't gain/lose any electrons to form ions.

chemical reactions

Grow, ripen, decay, and burn describe _____________ you can see ______________ change substances and rearrange atoms.

dissolving process

Many common solutions are solids dissolved in liquids. Gases can also dissolve in liquids. Solids can dissove in other solids. solvent molecules must exert more force on the particles of the substance than the particles exert on one another.

Solid

Particles in a solid are in fixed positions and can hold their shape without a container.(p.71)

Physical Properties

Physical properties: describe matter. You can use your senses to observe basic physical properties. Other physical properties: melting point, boiling points, strength, hardness, density, and the ability to conduct electricity, magnetism, or heat, can be measured. (p.46) Example: Copper conducts electricity well.(p.49) Example:Aluminum is used in foil because it is light, strong, and durable. (p.49 photo) Example: Boiling point is where the temperature of a liquid becomes a gas.

positive ion, or cation.

Removing or losing a single valence electron forms a

increasing temperature

Solutes dissolve faster when the solvent is hot. the particles of the solvent collide with undissolved solute more often.

Factors affecting reaction rate

Surface area, temperature, catalyst, concentration/pressure

Difference of a gas compared to a liquid or solid

The atoms and molecules in gases are much more spread out than in solids or liquids. They vibrate and move freely at high speeds. A gas will fill any container, but if the container is not sealed, the gas will escape. Gas can be compressed much more easily than a liquid or solid.

Characteristic Properties

The properties that are most useful in identifying a substance, such as density, solubility, and reactivity with acids, (p.52)

Universal solvent

Water,because many different substances

emulsion

a colloid in which liquids than normally do not mix are spread throughout each other

Non-polar compound

a compound whose electrons are equally distributed among its atoms - usually do not dissolve in water - do not have charges on opposite sides

Density

a measurement of how matter is contained in a certain volume of a substance and is a physical property Example of low density: helium filled balloons(p.47 pic) or (p.52 pic) Example of high density: golf ball (p. 48 paragraph 1)

Polar compound

a molecule that has an uneven distribution of electrons has distinct positively and negatively charged sides

Neutralization reaction

a reaction between an acid and a base Example: reaction of HCl and Magnesium hydroxide(antacid) and a base.

Synthesis

a reaction in which 2 or more substances combine for form a new compound(p.190) Example: metal sodium reacts with chlorine gas to form sodium chloride or table salt.(p.190) A + B → AB

Reactants

a substance or molecule that participates in a chemical reaction

Products

a substance that forms in a chemical reaction. energy must be added to break bonds. heat, electricity, sound, light.

pH scale

a value used to express the acidity or alkalinity of a solution. you must measure the concentration of hydronium ions. solutions that have a ph greater than 7 are basic. the hydroxide ions is greater than the concentration of hydronium ions. solutions that have a ph lower than 7 are acidic. the hydronium ions is greater than the concentration of hydroxide ions.

temperature and pressure

affect solubility of gases e.g. soda pop gaseous solutes are less soluble in warmer water(p.242) Example: Carbon dioxide gas is dissolved in an unopened bottle of soda. When the bottle is opened, the pressure inside the bottle decreases. Carbon dioxide gas then forms bubbles as it comes of solution.(p.242) just temperature affects solids and liquids

solution

all homogeneous mixtures

Acid

an compound that increases the number of hydronium ions when dissolved in water.(p.256) sour taste

Base

any compound that increases the number of hydroxide ions when dissolved in water. (p.258) bitter ,soapy taste feel slippery some bases contain hydroxide ion, OH-, but others do not.(p.258) bases cause indicators to change color, such as turning red litmus paper blue.

Anions

are altered names of elements. Oxygen, O ion name is oxide, symbol is O2-. Negatively charged ions

Ionic bonds

are formed between oppositely charged ions.

Ionic compounds

are formed by the strong attractions between cations and anions.(p.159) Names of cations include the elements of which they are composed. Example: Sodium, Na ion name is Na+.

Covalent bonds

are formed when atoms share 1 or more pairs of electrons.

Atoms

are made of protons, neutrons, and electrons. At the center of each atom is a small, dense nucleus with a positive electric charge. The nucleus is made of protons and neutrons. Atoms do not have a charge because they have an equal number of protons and electrons whose charges exactly cancel.

Elements and compounds

are pure substances, but mixtures are not.

Electron

are small particles that move around the outside of the nucleus and have a negative charge.

Metalloids/semiconductors

can conduct under certain conditions.

Liquids

change shape, but not volume. (p.72)

catalyst

change the rates of chemical reactions they are not reactants or products they speed up or slow reactions catalysts that slow reactions are called inhibitors.(p.207) enzymes are biological catalysts

Bohr's Model

compares electrons to planets.

Homogeneous mixtures

do mix evenly; the mixture is the same throughout. 4 examples: sugar and water; gasoline; carbonated drinks; oxygen; salt and water Miscible: mix together well.

Solid ionic compounds

do not conduct electricity because the charged ions are locked into place, causing the melting points to be very high.

Heterogeneous mixtures

don't mix uniformly and are not evenly distributed. 3 examples: flour and water; oil and water; salad Immiscible: don't mix together well.

Mass number

equals the number of protons plus the number of neutrons. (p.116) number of neutrons + atomic number(#protons) = mass number

Nonmetals

except for Hydrogen, are found on the right side of the periodic table; may be solids, liquids or gases; poor conductor of heat and electricity.

Valence Electrons

found in the outermost shell of an atom and that determines the atom's chemical properties.

Proton

has a positive charge

Radicals

have electrons available for bonding. It is when a covalent bond is broken such that at least one unpaired electron is left on each fragment of the molecule. react quickly to form covalent bonds with other substance, making new compounds.

Neutron

have no electric charge. mass number - atomic number(#protons) = Number of neutrons

temperature

heating food speeds up the chemical reactions that happen in cooking.(p.206) cooling food slows down the chemical reactions that result in spoiling food.

stirring/shaking

helps the solute dissolve faster.

Chemical Properties

include the reactivity of elements or compounds with oxygen, acid, water, and other substances. (p.50) Example: Iron turns to rust when exposed to oxygen. (p.50)

Double replacement

ions appear to be exchanged between compounds. AX + BY → AY + BX

Mixture

is a combination of 2 or more substances not chemically combined. Each substance in the mixture keeps its own properties.

Temperature

is a measure of the average kinetic energy of the particles in an object

Dissolving

is a physical change.(p.54)

Pure substance

is a sample of matter, either a single element or single compound, has definite chemical and physical properties. (p.41) Example: water H2O

Compound

is a substance made of atoms of two or more different elements are chemically combined. Example: nylon and rust (iron(III) oxide) Fe2O3

Element

is a substance that cannot be separated. e.g. Carbon C

Ions and Ionization

is an atom or group of atoms that has lost or gained one or more electrons and has a negative or positive charge. (p.115) Atoms that do not have filled outer s and p orbitals may undergo a process called ionization, which makes them reactive. They will gain or lose electrons so that they have a full outermost s and/or p orbital, so it will now be less reactive. (p.115) Atoms of Group 1 elements are reactive.

Matter

is anything that has mass and takes up space.

An organic compound

is covelently bonded compound made of molecules. Carbon atoms form 4 covalent bonds in organic compounds. They have 4 valence electrons to use for bonding.(p.166)

Atomic Mass Unit

is equal to 1/12 of the mass of a carbon-12 atom and describes the mass or molecule of an atom.

A metallic bond

is formed by the attraction between + charged metal ions and negative electrons around them. The electrons move freely between metal atoms, so they conduct electricity.

The difference between a colloid and a suspension

is that the particles in colloids are smaller than those in suspensions. Those smaller particles can pass through the filter and stay dispersed in the mixture.

Sublimation

is the process by which a solid turns directly into a gas. Sometimes ice sublimes to form a gas. (p.75)

Molecules

is the smallest unit of a substance. Chemically combined that keeps all the physical and chemical properties of that substance.(p.40) Example: 2 H2O H2 H2O has 2 hydrogen atoms and 1 oxygen atom

Atom

is the smallest unit of an element and is matter.

solvent in a solution

is the substance in which the solute dissolves.

solute in a solution

is the substance with a larger surface area that dissolves the solvent faster.

Homogeneous mixtures

look and are uniform. Example: salt water

Miscible liquids

mix to form solutions. Not so easy to separate.

For 2 element covalent compounds

numerical prefixes tell how many atoms of each element are in the molecule. Example: dinitrogen tetroxide has 2 nitrogen atoms and 4 oxygen atoms.(p.162) N2O4

A chemical change

occurs when a substance changes composition by forming one or more new substances. - causes changes in color e.g when fruit ripens), or produced sound, light, odor, or heat

Dalton's theory

proposed that atoms could not be divided. According to Dalton, all atoms of a given element were exactly alike. Dalton also stated that atoms of different elements could join to form compounds. Atoms are the building blocks of molecules

concentration/pressure

react faster Example: a gas at high pressure is more concentrated that the same amount of a gas at a low pressure. Gases react faster at higher pressures; the particles have less space, so they have more collisions.

The kinetic theory of matter

says all matter is made of atoms and molecules that act like tiny particles and they are always in motion. The higher the temperature of the substance, the faster the particles move. At the same temperature, heavier particles move slower than light particles

Finding oxidation numbers from formulas

see chart or notes given

3 common states of matter

solid, liquid, gas

The law of conservation of mass

states that mass cannot be created or destroyed

Chemical energy

stored or conserved energy

Atomic number

tells you how many protons are in an atom.

Chemical Bonds

the attractive forces that hold different atoms or ions together in compounds. (p.145) Compounds are always made of the same elements in the same proportion.(p.145) When 2 atoms join, a bond forms. Atoms bond when their valence electrons interact.(p.151) Atoms with full outermost s and p orbitals are more stable than atoms with only partly filled outer s and p orbitals.

Single replacement

the elements trade places. AX + B → BX + A all alkali metals and some other metals

Solubility

the maximum amount of a solute that will dissolve in a given quantity of solvent at a given temperature and pressure.

Chemistry

the scientific study of matter and all the changes that matter undergoes.

Energy must be absorbed

to melt the ice into water.

Immiscible liquids

to separate two immiscible liquids is to carefully pour the less dense liquid off the top.

Energy must be released

to solidity water into ice

Combustion

uses oxygen as a reactant.(191) at least one product always contains oxygen water is a common product.

increasing surface area

when a solid is crushed into small pieces, it dissolves faster than the same substance in large pieces. dissolved sugar molecules will slowly diffuse, or spread out, through the entire solution.(p.237)