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valence electron

electrons that have the highest energy level and are held most loosely. These are the electrons involved in bonding

chemical bond

force of attraction that holds two atoms together as a result of rearrangement of electrons

octet rule

8 valence electrons is stable


atom or group of atoms that have an electric charge

polyatomic ion

ions that are made of more than one atom and react as a unit

ionic bond

attraction between two oppositely charged ions. Forms as a result of attraction between positive and negative ions. Usually occurs between a metal and a non-metal

ionic compound

contains ionic bonds

Properties of ionic compounds

strong bonds, high melting points, conduct electricity when dissolved in water


neutral group of atoms joined by covalent bonds

covalent bond

chemical bond formed when two atoms share electrons usually occurs between two non-metals


postive ion, forms when atom loses electrons


negative ion, forms when atom gains electrons

molecular compound

contains atoms that are covalently bonded

Double bond

when atoms share 2 pairs of electrons

Triple bond

when atoms share 3 paris of electrons

Properties of molecular compounds

weaker bonds, low melting and boiling points, don't conduct electricity when dissovled in water

Polar covalent bond

when electrons are shared unequally between atoms, one atom is pulling more on the electrons, causing a slight charge on the atoms

Non-polar covalent bond

when electrons are shared equally between atoms, all atoms pull equally on the electrons, so no charge on the atoms


mixture made of two or more elements that have properties of a metal. At least one must be a metal. Usually less likely to react with air and water than pure metals they are made of.

physical change

only alters the appearance or form of the substance

chemical change

a new substance is made. Bonds are broken and reformed during this reaction

Signs of a chemical reaction

new substance formed and change in energy always occur. Can see a change in color, bubbles, or a precipitate


solid forming from solution during a chemical reaction

Endotheric reaction

Energy is taken in by the reaction and the products have more energy than the reactants

Exothermic reaction

energy is released by the reaction and the products have less energy than the reactants

Conservation of mass law

Mass can not be created nor destroyed during a chemical reaction. This is why chemical equations must be balanced.

Open system

Matter is able to leave the reaction area and is not easily collected

Closed system

All matter is contained in a sealed container

Synthesis reaction

two or more elements combine to make a more complex substance

Decomposition reaction

breaks down compounds into simplier products

single replacement reaction

one element replaces another in a compound

double replacement reaction

elements in one compound appear to trade places with elements of the other compound

activation energy

minimum amount of energy needed to start a chemcial reaction


material that increases the rate of a reaction by lowering the activation energy. Provides a surface for the reaction to take place


biological catalyst contained in human cells. Only works under certain conditions


materal used to decrease the rate of reaction, prevents the reactants from forming the product

surface area

an increase of this causes more particles to be exposed to the reactant and increases the rate of the reaction


an increase of this causes the paricles of the reactant to speed up and collide with each other more often, which speeds up the reaction rate


an increase of this causes more reactants to be in a confined area, this causes them to collide more often and increases the reaction rate


found on the left side of a chemical equation, what you start the chemical reaction with


found on the right side of the equation, what you end up with after a chemical reaction


small number below an atom in a compound, tells ration of atoms in a compound


a number written in front of a chemical formula (symbol for compound) to indicate the number of molecules present in a chemical equation/reaction

chemical formula

symbols used to show what elements are in a compound

chemical equation

the short and easy way to show what happens in a chemical reaction

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