Atomic radius is the distance measured from the nucleus to the outer valence electrons – measured in pm picometres which is 1x10-12 m
Atomic radius is the measure of the distance from the centre of the nucleus to the outer electron.
Group 1 is the first group in the periodic table containing elements that are commonly known as the Alkali metals. They are all metals and increase in reactivity down the group and when reacted with water form alkali solutions
The Halogens in Group 17 are non metal elements that are diatomic and simple covalently bonded. They decrease in reactivity down the group but increase in their melting and boiling points.
The lanthanides are a series of chemicals in the expanded periodic table that have an expanded number of orbitals beyond that of the transition metals. The lanthanides are mostly soft metals with their hardness increasing across the period. Whilst they are metals and can conduct electricity the lanthanides have a relatively high resistivity.