Written below are some important chemistry terms along with their definitions.
Please feel free to add any new terms and/or edit the definitions of the pre-existing terms below.
Please add in the proper alphabetical order. Thanks.

A-C

Atom-The smallest particle of a chemical element that consists of electrons, protons, and neutrons.
Addition reaction- A reaction where atoms add to a carbon-carbon multiple bond.
Adsorption- When one substance collects of the surface of another one.
Alcohol- An organic molecule containing an -OH group
Aldehyde-An organic molecule containing a -COH group
Alkali metals- Group I in the periodic table.
Alkaline earth metals- Group II in the periodic table.
Alkane- An organic molecule which contains only single carbon-carbon bonds.
Alkene- An organic molecule containing at least one C=C bond
Alkyne- An organic molecule containing at least one C-C triple bond.
Allotropes- When you have different forms of an element in the same state. The relationship that white phosphorus and red phosphorus have to each other is that they're allotropes.
Chemical Changes-A chemical reaction in which one or more substances are converted into another new substance.
Chemical Property-How a chemical reacts with other chemicals.
Chemistry-The study of matter and its properties at the molecular level.
Compound-When two or more different atoms are combined
Condensation-The process in which gas changes into liquid.

D-H

Decantation-Pouring the liquid off the top of a mixture.
Deposition-The process in which a gas changes directly into a solid.
Element-Consists of only one specific type of atom.
Emulsion- Particles are very tiny.
Endothermic-A chemical reaction that absorbs heat, producing products with more potential energy than the reactants.
Exothermic-A chemical reaction that releases heat, producing products with less potential energy than the reactants.
Extrinsic Property-Characteristics of a substance that are dependent on the amount of the substance; Also known as Extensive Property.
Filtration- Uses a porous barrier to separate a solid from a liquid.
Heterogeneous Mixture-A mixture that consists of different substances or phases.
Homogeneous Mixture-A mixture with the same uniform appearance and composition throughout.

I-O

Inference-An educated guess based on collected information.
Intrinsic Property-Characteristics of a substance that are NOT dependent on the amount of the substance; Also known as Intensive Property.
Kinetic Energy-Is moving energy.
Matter-Anything that has matter or volume.
Mixture-Combination of two or more pure substances that can be separated by physical means.
Molecule-A substance with two or more atoms chemically combined.
Observation-The act of gathering facts using our five senses.

P-S
Physical Change-A change in the physical appearance of a substance that does not change the identity of the substance.
Physical Property-The characteristics of chemical when it is by itself.
Potential Energy-Is stored energy.
Solidification-The process in which a liquid changes into a solid.
Sublimation-The process in which a solid changes directly into a gas.
Suspensions- Large particles are floating in the liquid or gas medium.