Atomic Structure and Periodic Table

Atom

Smallest stable particle of matter. It is the smallest piece of an element that can still be recognised as that element.

Nucleus

Central part of the atom, containing protons and neutrons (collectively known as nucleons).

Proton

Positively charged sub-atomic particle with a relative mass of 1, found in the nucleus.

Electron

Negatively charged sub-atomic particle with relative mass of nearly. 0, found orbiting the nucleus.

Neutron

Uncharged sub-atomic particle with relative mass of 1, found in the nucleus.

Atomic Number

Number of protons in the nucleus of an atom (bottom number on the Periodic Table).

Mass Number

Total number of protons and neutrons in the nucleus of an atom (top number on the Periodic Table).

Sometimes known as the nucleon number.

Relative atomic mass

Weighted average mass of the isotopes of an atom of an element, relative to an atom of Carbon-12, which has a mass of exactly 12 units.

Isotope

Atoms of the same element with the same number of protons (same atomic number) but different numbers of neutrons (therefore different mass number).

Electron shell/energy level

Where electrons orbit the nucleus.

Electron structure/configuration/arrangement

Shows the number of electrons on each shell on an atom (e.g. Na = 2,8,1)

Valence Shell/Electrons

The outermost shell of electrons (highest energy level).

Group

A vertical column of elements on the Periodic Table.

Period

A horizontal row of elements on the Periodic Table.

Periodic Table

A table showing all the known elements, arranged in order of atomic number.

Alkali Metals

Group 1 elements

Halogens

Group 7 elements

Noble Gases

Group 0 elements, unreactive