Important Chemistry Terms

Atomic Mass

The total mass of a single atom, mostly made up of its protons and neutrons. Measured in amu (amu is the same number as mass in grams).

Atomic Number

The count of protons inside the middle part or nucleus, of an atom. (Also the position number in the periodic table)

Molar Mass

The mass of one mole of a substance. It is measured in grams per mole (g/mol)

Ion

An atom or small group of atoms that has an electrical charge and gets this charge by losing or gaining electrons.

Cation

A positively charged ion. It forms when an atom loses elections. (more protons than electrons)

Anion

A negatively charged ion. It forms when an atom gains electrons. (more electrons than protons)

Isotope

When forms of the same chemical element have the same number of protons but a different number of neutrons.

Binary Molecular Compounds

Formed from two different non-metal elements. Atoms share electrons via covalent bonds. They do not form charged ions. Example: CO₂

Binary Ionic Compounds

Formed from two different elements: One metal and one non-metal. The metal gives electrons to the non-metal to form positive and negative ions. Example: NaCl

Ternary Ionic Compounds

Formed from three or more different elements. They include a metal combined with a polyatomic (many-atom) ion, or sometimes an ammonium cation with a non-metal. Examples KNO₃

Formula Unit

the lowest whole-number ratio of ions or atoms in a (1:1) non-molecular substance

Diatonic

a molecule that is made up of exactly two atoms (BrINClHOF → Br₂, I₂, N₂, Cl₂, H₂, O₂, F₂, )