Grade 10 · Theory
Isotopes and relative atomic mass
Atomic structure · about 3 min
Visual overview: Isotopes and relative atomic mass1 MIN READ
2 study sections · pause after each one and recall the key ideaAtoms of the same element can differ in neutron count, which explains non-whole-number atomic masses.
Key points- Isotopes have the same Z but different A (¹²C and ¹⁴C).
- Isotopes behave identically chemically because the electron arrangement is the same.
- Relative atomic mass is the weighted average of the isotopes by abundance.
- Weighted average = Σ(mass × percentage abundance) ÷ 100.
- Isotope — same element, different number of neutrons.
- Relative atomic mass — the abundance-weighted average mass.
EXAM TIP
check your weighted average sits between the isotope masses and nearer the more abundant one.