Atomic Structure and the Periodic Table

Atoms are incredibly tiny - about 0.1 nanometres across - but they're made up of three main particles. Protons (positive charge) and neutrons (no charge) sit in the nucleus at the centre, whilst electrons (negative charge) whiz around in shells outside.

The atomic number tells you how many protons an element has, and this determines what element it is. Isotopes are atoms of the same element with different numbers of neutrons - they behave chemically the same but have different masses.

Dmitri Mendeleev created the first proper periodic table by arranging elements by atomic weight and leaving gaps for undiscovered elements. Brilliant move! The modern periodic table arranges elements by atomic number, with metals on the left and non-metals on the right.

Groups (columns) contain elements with similar properties because they have the same number of outer electrons. Periods (rows) show elements with the same number of electron shells. This organisation makes predicting element behaviour much easier!

Quick Tip: The group number tells you exactly how many electrons are in the outer shell - dead useful for understanding reactivity!