How does the electronegativity of elements depend on atomic size?
Electronegativity can be thought of as the ability of an atom to pull the bonding pair of electrons towards itself. The more electronegative an atom is, the closer the bonding pair will be to it. Metals generally have low electronegativity, while non-metals have higher values of electronegativity. When the electronegativity difference between the bonding atoms is high, we get an ionic bond. When the bonding atoms have similar electronegativity, we get a non-polar covalent bond.
Electronegativity is dependent upon the size of the atom, since the attraction for electrons falls rapidly as the distance from the nucleus increases. The larger the atom gets, the more distant electrons become from the nucleus and hence have lesser attraction to the atom. That is why electronegativity decreases as we go down a group in the periodic table. This is because between each successive group member (as we go down), an extra electron shell is added to the atom and the bonding electrons become more distant from the nucleus. However, when we move across a period in the periodic table, electronegativity increases, since the atomic size decreases across a period.
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