Atomic number (Z)

Definition

The atomic number (Z) is the number of protons found in the nucleus of an atom. It determines the element's identity and its position on the periodic table.

5 Must Know Facts For Your Next Test

1. 1. The atomic number is unique to each element and defines the type of atom.
2. 2. In a neutral atom, the atomic number also equals the number of electrons.
3. 3. The periodic table is arranged in order of increasing atomic number.
4. 4. The symbol for the atomic number is Z.
5. 5. Changes in the atomic number result in a different element.

Review Questions

• What does the atomic number represent?
• How does the atomic number determine an element's position on the periodic table?
• What happens if you change an atom's atomic number?

Related terms

Mass Number:

The total number of protons and neutrons in an atom's nucleus.

Isotope:

Atoms of the same element with different numbers of neutrons and hence different mass numbers.

Periodic Table:

A tabular arrangement of elements ordered by increasing atomic number, which displays recurring chemical properties.