What term refers to how strongly an atom of an element attracts electrons in a chemical bond with an atom of a different element?

#"Electronegativity"# refers to the tendency of an atom in a chemical bond to polarize electron density towards itself. There are various scales, of which #"Pauling Scale"# was the earliest, and is still most widely used. Electronegativity increases across a Period of the Periodic Table (from left to right as we face it), and DECREASES down a Group, a column of the Table.

Elements towards the right of the Periodic Table as we face it, with high nuclear charges, e.g. oxygen, fluorine, tend to have high electronegativities. Why? Because the high nuclear charge acts on the valence electrons, contracting the valence shell. When a Period is filled on the Periodic Table, electrons add to the next shell, and valence electrons are somewhat shielded from the increased nuclear charge.

When we look at molecules which combine strongly electronegative elements with moderately electronegative elements, such as #OH_2#, or #H-F# or #NH_3#, we conceive that the individual bonds become polarized. That is charge separation occurs to give #""^(delta+)H-O^(delta-)-H^(delta+)#, #""^(delta-)F-H^(delta+)# and #""^(delta-)NH_3^(delta+)#, where there are partial electric charges on the participating atoms.