Describe the trend for electronegativity on the periodic table

Electro-negativity is a property of an element to attract shared pair of electrons towards itself in chemical bond.

The electro-negativity character decreases down the group because due to addition of new energy levels or shells valence electrons moves far away from the nucleus. The electro-negativity character increases across the period because of increase in number of protons and electrons by one unit. New electrons enters in the same energy level with strong nuclear effect exerted by the nucleus on them by which they tend to attract valence electrons closer to the nucleus.