Atomic structure

The foundation of chemistry: what atoms are made of, how to read the periodic table, isotopes, electron shells, ions, and why the noble gases are so unreactive.

Everything in chemistry starts with the atom. This track builds from what chemistry studies and how the periodic table is organised, down to the three subatomic particles: protons, neutrons and electrons.

It then explains atomic number and mass number, why isotopes are the same element with different weights, how electrons fill shells, and why atoms form ions and chase the full-shell stability of the noble gases.

What you will learn:

  • What chemistry is, elements, and the periodic table
  • The atom and its protons, neutrons and electrons
  • Atomic number, mass number and isotopes
  • Electron shells, ions, and the noble gases

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Frequently asked questions

What is the difference between atomic number and mass number?
The atomic number is the number of protons, which defines the element. The mass number is the total of protons and neutrons, so subtracting the atomic number from it gives the neutron count.
What are isotopes?
Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons. They are chemically identical but have different masses, which is why many periodic-table masses are not whole numbers.

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