Atomic number

Definition

The atomic number is the number of protons in the nucleus of an atom. It determines the chemical properties of an element and its place in the periodic table.

5 Must Know Facts For Your Next Test

1. The atomic number is represented by the symbol 'Z'.
2. Elements are arranged in the periodic table in order of increasing atomic number.
3. An atom's identity as a specific element is defined by its atomic number.
4. Isotopes of an element have the same atomic number but different numbers of neutrons.
5. The atomic number also defines the electron configuration and reactivity of an element.

Review Questions

• What does the atomic number represent?
• How does the atomic number affect an element's position on the periodic table?
• Why do isotopes of an element share the same chemical properties?

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 thus different mass numbers.

Ion: An atom or molecule with a net electric charge due to the loss or gain of one or more electrons.