Define electronegativity and describe its periodic trends. How do you show which element has the higher electronegativity in a covalent bond?

Electronegativity is the ability of the atom in a covalent bond to attract the shared pair of electrons.

Higher value of electronegativity, more strongly the element attracts shared electrons.

Electronegativity variation:

Electronegativity decreases from the top to bottom in the groups, and increases from the left to right across the periods.

This is because of the size which increase down the group and decreases across the period.

Thus, fluorine is most electronegative element, while francium is the least electronegative element.

The electrons in which the covalent bond are shared unequally when the there is significant electronegative difference. These bonds are known as polar covalent bonds. More electronegative atom has partial negative charge because electrons spend more time as it is closer to the atom, while less electronegative atom has partial positive charge because electrons are partly pulled away from the atom.

Thus, the atom which bears a partial negative charge has higher electronegativity in a covalent bond.