Electronegativity describes the tendency of atoms to gain electrons forming negative ions.  The halogens ..Periodic Table Group VIIA(col 17): are typical electronegative ions.. Considering the hydrogen chloride molecule the chlorine atom is more electronegative than the hydrogen atom and consequently the molecule is polar.  The chlorine atom has a negative charge.

The most common method of assigning values to this property is to use the Pauling scale.  This is based on the bond dissociation energies for which fluorine, the most electronegative element, is given a value 4

The electronegativity to can be used to estimate whether a given bond will be nonpolar covalent, polar covalent, or ionic.   It is expected that the electronegativity of an atom in a molecule to be related to its ionization energy and electron affinity, which are properties of isolated atoms.

It is possible to use the difference in electronegativity between two atoms to gauge the polarity of the bonding between them.   The greater difference in electronegativity, the more polar the bond.   Compounds with an electronegativity (EN) difference δEN > 1.7 are generally classified as ionic; those with δEN < 1.7 are covalent.