Final answer:
Electronegativity is the measure of an atom's ability to attract electrons when it is part of a compound, indicating how ionic or covalent a bond will be. Electronegativity values increase from left to right across the periodic table, contrasting with valency, which is based on the number of electrons available for bonding.
Step-by-step explanation:
Definition: Electronegativity
Electronegativity is the measure of an atom's ability to draw electrons into itself in the formation of a covalent bond. It is a relative measure that indicates how strongly an atom attracts electrons when it forms a covalent bond. The concept is vital in understanding the nature of the bonds within a molecule and the overall reactivity and properties of the molecule.
The valency of an atom refers to the number of electrons in the outer shell that are available to form bonds with other atoms. This is different from electronegativity, which focuses on the attraction of an atom for electrons when it is part of a compound.
Electronegativity values typically increase from left to right across the periodic table. The degree to which a given bond is ionic or covalent can be determined from the difference in electronegativity between the two atoms involved in the bond. A high electronegativity value indicates a greater attraction for electrons, leading to more ionic character in the bond.