What does electronegativity measure?

Electronegativity measures the ability of an atom to attract electrons towards itself when it is involved in a chemical bond. This concept is crucial in understanding how atoms interact and form molecules. Atoms with high electronegativity have a stronger pull on the shared electrons within a bond, influencing the bond's characteristics and the behavior of the resulting compound.

For instance, in a covalent bond between two different atoms, the atom with higher electronegativity will attract the electrons more strongly, leading to a polar bond. This property is essential in predicting the behavior of molecules in chemical reactions and their physical properties.

The other choices do not relate to the concept of electronegativity. The size of an atom refers to its atomic radius, the amount of energy in an atom relates to its energy levels and states, and the number of protons in an atom reflects its identity as an element, which does not directly correlate with how it attracts electrons.