Atomic Structure and Isotopes

Atomic Structure and Isotopes

An atom has a tiny, dense nucleus (containing protons and neutrons) surrounded by electrons in shells. Protons are positive, electrons are negative, and neutrons have no charge.

Atomic and mass number

The atomic number is the number of protons (which defines the element). The mass number is protons plus neutrons combined.

Isotopes

Isotopes are atoms of the same element with the same number of protons but a different number of neutrons — meaning the same atomic number but a different mass number.

Practice

Carbon-12 and Carbon-14 are both carbon. What's different between them, and what's the same?