Atom: The smallest unit of an element that still has its properties
Molecule: Two or more atoms joined together
Element: A pure substance made of only one kind of atom
Compound: A substance made of two or more elements chemically joined
Mixture: Two or more substances together but not chemically joined
Proton: Positive particle in the nucleus
Neutron: Particle with no charge in the nucleus
Electron: Tiny negative particle that moves around the nucleus
Nucleus: The center of an atom, holding protons and neutrons
Ion: An atom or group of atoms with an electric charge
Cation: A positive ion
Anion: A negative ion
Ionic bond: A bond formed when electrons move from one atom to another
Covalent bond: A bond formed when atoms share electrons
Metallic bond: A bond in which electrons flow freely among metal atoms
Chemical formula: Symbols and numbers showing what atoms make up a substance
Chemical reaction: A process in which substances change into new substances
Reactant: A starting substance in a chemical reaction
Product: A substance made by a chemical reaction
Chemical equation: A way to show a reaction using formulas
Law of conservation of mass: Matter is not created or destroyed in a chemical reaction
Catalyst: A substance that speeds up a reaction without being used up
Enzyme: A biological catalyst, made of protein
Solution: A mixture that is the same all the way through
Solute: The substance that is dissolved
Solvent: The substance that does the dissolving
Solubility: How much of a substance can dissolve in a solvent
Concentration: How much solute is in a certain amount of solution
Saturated solution: One that cannot dissolve any more solute
Suspension: A mixture with particles that settle out if left alone
Colloid: A mixture with tiny particles that stay spread out, like milk
Density: How much mass is in a given volume
Mass: The amount of matter in an object
Volume: The amount of space something takes up
Physical change: A change in form that does not make a new substance
Chemical change: A change that makes new substances
Physical property: A trait you can observe without changing the substance, like color
Chemical property: How a substance can change into another, like flammability
Exothermic reaction: A reaction that gives off heat
Endothermic reaction: A reaction that takes in heat
Oxidation: A reaction in which a substance loses electrons or combines with oxygen
Reduction: A reaction in which a substance gains electrons
Precipitate: A solid that forms from a liquid solution during a reaction
Distillation: Separating liquids by boiling and condensing them
Filtration: Separating solids from liquids using a filter
Evaporation: A liquid changing to a gas at its surface
Condensation: A gas changing into a liquid
Mole: A unit for counting atoms: 6.02 x 10^23 particles
Avogadro's number: 6.02 x 10^23, the number of particles in one mole
Molar mass: The mass of one mole of a substance
Valence electron: An electron in the outer shell that takes part in bonding
Atomic number: Number of protons in an atom
Mass number: Protons plus neutrons in an atom
Isotope: Atoms of one element with different numbers of neutrons
Radioactivity: The giving off of energy and particles by unstable atoms
Half-life: Time it takes half of a radioactive sample to decay
Polymer: A large molecule made of many repeating units
Organic compound: A compound built on carbon, usually with hydrogen
Allotrope: One of different forms of the same element, like diamond and graphite
Alloy: A mixture of metals, such as brass or steel
Corrosion: The slow wearing away of metal by chemical reaction
Combustion: Burning: a fast reaction of a fuel with oxygen
Synthesis reaction: Two or more substances combine to make one product
Decomposition reaction: One compound breaks down into simpler substances
Electrolysis: Using electricity to split a compound
Inert: Not reacting easily with other substances
Reactivity: How easily a substance takes part in chemical reactions
Malleable: Able to be hammered into thin sheets
Ductile: Able to be pulled into wire
Conductor: A material that lets heat or electricity flow easily
Insulator: A material that does not let heat or electricity flow easily
Electronegativity: How strongly an atom pulls on shared electrons
Periodic law: Element properties repeat in a pattern as atomic number goes up

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