Periodicity

'Periodicty is the word given to the fact that elements in the periodic table show a repeating pattern of properties in each row (period)'

The Periodic Table

• Arranges elements in order of increasing atomic number
• Consists of horizontal rows, or periods and vertical columns or groups
• It is split into several blocks, in each block the elements have their outermost electron in a particluar type of orbital
• Elements in the same group have the same number of electrons in their outer shell. For elements in group 1-7 the number of outer shell electrons is the same as the group number. For elements in group 8 they have a ful outer shell

The outer electron configuration shows periodicity; that it varies in roughly repeating patterns across each period of the periodic table

• Because many physical and chemical properties are influenced by the outer shell configuration of an atom, the properties also exhibit periodicity. These properties include; ionisation energy, atomic radius, ionic radius, melting points and boiling points

Ionic Radius: Increases down the group, decreases across a period

Ionisation Energy: Decreases down the group, increases across a period

The halogens show increasing boiling point down the group due to increasing van der Waals forces between molecules

Reactivity and Periodicity

• For the metals, the reactivity increases moving down the group
• This can be explained by ionisation energies. The group 1 metals will lose an electron to make an ion with a 1+ charge. The less energy needed to remove the electron, the more likely it is to happen and therefore the more reactive the metal
• Ionisation energy decreases down the group, so reactivity decreases
• For non-metals the situation reverses
• This is because the atoms gain an electron, so the more attraction there is between the outer electrons and the nucleus, the more reactive it is