Elements in the periodic table are organised into groups and periods. Explain what is meant by the terms 'group' and 'period', and describe how knowing an element's position in the periodic table can be used to predict its properties.

A group is a vertical column of the periodic table. Elements in the same group have similar chemical properties because they have the same number of valence electrons. A period is a horizontal row of the periodic table. Elements in the same period have the same number of electron shells. Knowing an element’s position allows us to predict its behaviour: the group tells us about its typical reactions and bonding, while the period tells us about its size, ionisation energy and electronegativity.