Chemistry (Terms)

Matter

Any substance that occupies space and has mass.

Atom

The smallest unit of matter that retains the properties of an element.

Element

A substance made up of only one type of atom.

Compound

A substance made of two or more different elements chemically bonded

Molecule

A group of two or more atoms held together by chemical bonds

Proton

A positively charged subatomic particle

Neutron

A neutral subatomic particle

Electron

A negatively charged subatomic particle

Nucleus

Central core of an atom, composed of protons and neutrons

Electron orbitals

Layers around an atom's nucleus where electrons orbit the nucleus

Atomic number

Number of protons in a nucleus

Mass number

The sum of protons and neutrons in the nucleus

Neutral atom

An atom with the same number of protons and electrons.

Ions

An ion is an atom or molecule that has an unequal number of protons and electrons, resulting in a net electrical charge

cation

Ions which have a positive charge

anion

Ions which have a negative charge

Valence electrons

Electrons in the outermost energy level of an atom.

Periodic Table

A table of all elements according to their atomic number, identifying elements with similar chemical properties.

Octet rule

Atoms tend to establish completely full outer energy levels. (8 valence electrons, with exc. hydrogen - 2)

[Atoms with full energy levels are less reactive than atoms with unfilled energy levels]