Glossary

Group
A vertical column in the periodic table. Members of a group typically have similar properties and electron configurations in their outer shell.

Period
A horizontal row in the periodic table. The atomic number of each element increases by one, reading from left to right.

Block
Elements are organised into blocks by the orbital type in which the outer electrons are found. These blocks are named for the characteristic spectra they produce: sharp (s), principal (p), diffuse (d), and fundamental (f).

Atomic number
The number of protons in an atom.

Electron configuration
The arrangements of electrons above the last (closed shell) noble gas.

Melting point
The temperature at which the solid–liquid phase change occurs.

Boiling point
The temperature at which the liquid–gas phase change occurs.

Sublimation
The transition of a substance directly from the solid to the gas phase without passing through a liquid phase.

Density (g cm⁻³)
Density is the mass of a substance that would fill 1 cm³ at room temperature.

Relative atomic mass
The mass of an atom relative to that of carbon-12. This is approximately the sum of the number of protons and neutrons in the nucleus. Where more than one isotope exists, the value given is the abundance weighted average.

Isotopes
Atoms of the same element with different numbers of neutrons.

CAS number
The Chemical Abstracts Service registry number is a unique identifier of a particular chemical, designed to prevent confusion arising from different languages and naming systems.