Electronegativity

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Electronegativity

Electronegativity - A measure of the tendency of an atom to attract a bonding pair of electrons.

Electronegativity increases as you go across a period. It decreases as you go down a group.

Electronegativity depends on the number of protons in the nucleus, the distance from the nucleus of the bonding pair of electrons and how much shielding there is from inner electrons.

Going across the period:

The bonding pair of electrons will be shielded by the same number of electrons. However, the number of protons will increase, so the group 7 element will be more electronegative than the group 1 element.

Going down a Group:

There is more shielding from inner electrons and the bonding pair of electrons are further from the nucleus. This adds up to less pull on the bonding pair from the positive charge of the nucleus and so electronegativity decreases.

Trends in the periodic table:

Usually identified across periods or down groups.

However, there are often similarities between elements that are diagonal to each other.

I.e./ Beryllium and Aluminium have identical electronegativity.

There is an increase across the period from group 2 to group 3 but then as electronegativity decreases down a group, this increase is balanced out.

Other diagonal pairs also have similar electronegativity, i.e./ Lithium and Magnesium.

These similarities mean they form similar bonds.