The tendency of an atom to attract a shared pair of electrons towards itself is known as electronegativity. When we move from top to bottom in a group, electronegativity decreases. The tendency of an atom to attract bonded electrons towards itself depends on the number of protons in the nucleus, the distance of bonded electrons from the nucleus and the amount of screening by inner electrons. When moving down the group, the distance of the shared pair of electrons from the nucleus increases which decreases the ability of the atom to attract these electrons. Moreover, shielding effect increases which reduces the effective nuclear charge on the electron cloud.