What is Electronegativity?

Electronegativity is how strongly an atom pulls on the electrons it shares in a chemical bond. When two bonded atoms pull unequally, the shared electrons sit closer to the stronger atom — that end becomes slightly negative, the other slightly positive. Such a bond is called polar.

The pull is scored from about 0.7 to 4.0 on the Pauling scale, with fluorine at 4.0 pulling hardest, and electronegativity rises going right and going up the periodic table, so fluorine, oxygen and nitrogen pull strongly while bottom-left metals barely pull. What a bond becomes depends on the gap between the two atoms' values. A small gap, as in carbon and hydrogen, means nearly even sharing, which is a nonpolar bond. A medium gap, as in oxygen and hydrogen, means shared but shifted, giving a polar bond with a negative end and a positive end. A large gap, as in sodium and chlorine, means the stronger atom takes the electron outright and both become ions, which is an ionic bond. The consequence is everywhere: water's polar bonds make each molecule a tiny magnet, which is why water dissolves salt.

Two people, one blanket: equal sleepers keep it centered all night — fair share, nonpolar — while one blanket hog drags it to their side, leaving the other person not blanket-less but cold and slightly bitter: a polar arrangement, one side covered, one exposed. The extreme case is the hog taking the whole blanket and rolling over — nobody calls that sharing, just two separate sleep situations held together by the bed. That's ionic, and the hog's pull strength is electronegativity.