Electronegativity is a measure of an atom's ability to attract electrons to itself when it is part of a chemical bond. It is a relative property, and it varies depending on the type of bond that is formed. Atoms with high electronegativity values tend to have a strong tendency to attract electrons, while those with low electronegativity values do not. For example, fluorine has a very high electronegativity, which means that it is very good at attracting electrons when it forms a bond with another atom. In contrast, sodium has a low electronegativity, which means that it does not have a strong tendency to attract electrons when it forms a bond.