Group 2 - as an example of properties in a group

s block elements in which the outermost electrons are in a full s sub-shell.

Trends in physical properties

Data is not known accurately for the last member of the group – radium.

Element	Electronic Configuration	Atomic radius /nm	1^st Ionisation energy kJ mol^-1	Electronegativity	Melting point /K
Be	[He]2s²	0.089	899	1.5	1551
Mg	[Ne]3s²	0.136	737	1.2	924
Ca	[Ar]4s²	0.174	590	1.0	1116
Sr	[Kr]5s²	0.191	549	0.95	1042
Ba	[Xe]6s²	0.198	503	0.89	998

Atomic radius of Group II

Going down the group atomic radii increases.

The number of electron shells increases

The outermost electrons are progressively further from the nucleus

First Ionisation energy

This decreases down the group because:

o Atomic radius increases

o Outermost electrons become increasingly shielded from the positive charge of the nucleus.

Electronegativity

This decreases down the group – Be is the most electronegative.

Bonds formed by beryllium are covalent.

Even if a halogen bonds with a small highly charged Be ion, electron density is drawn from the negative ion

Shape of negative ion is distorted and electron density is concentrated between the two atoms so that a pair of electrons is shared and the bond is essentially covalent.

As the size of the ion increases down the group, the polarising power decreases as the charge-to-size ratio decreases.

Ca, Sr and Ba are essentially ionic.