Electronegativity is a measure of the tendency of a bonded atom to attract electrons to itself.
The electronegativity of elements to the right and top of the periodic table is higher.
Covalent bonds are classed as polar if the bond is between atoms of elements having different electronegativities.
The term polar is used because the sharing of electrons in these bonds is unequal with the electron density being higher at the more electronegative atom. This atom has a partial negative charge (δ–) and the other atom in the bond has a partial positive charge (δ+).
The red and blue colours in graphic showing the distribution of electrons in the hydrogen fluoride molecule shows a partial negative charge (δ–) at fluorine (red) and a partial positive charge (δ+) at hydrogen (blue). This is due to fluorine being more electronegative than hydrogen.
Diatomic molecules (two atoms such as HF) are polar (have atoms with partial negative and positive charges) if the atoms are different because the electronegativities of the atoms will be different.
| Electronegativity |  | H 2.2 |  | He | ||||
| Li 1.0 | Be 1.6 | B 2.0 | C 2.6 | N 3.0 | O 3.4 | F 4.0 | Ne | |
| Na 0.93 | Mg 1.3 | Al 1.6 | Si 1.9 | P 2.2 | S 2.6 | Cl 3.2 | Ar | |
| K 0.82 | Ca 1.0 | Ga 1.6 | Ge 1.8 | As 2.2 | Se 2.6 | Br 3.0 | Kr | |
| Rb 0.82 | Sr 0.95 | In 1.8 | Sn 2.0 | Sb 2.1 | Te 2.1 | I 2.7 | Xe | |
| Cs 0.79 | Ba 0.89 | Tl 1.6 | Pb 2.3 | Bi 2.0 | Po 2.0 | At | ||
The electronegativity of elements to the right and top of the periodic table is higher.
Metals are less electronegative than non-metals.
Hydrogen has a lower electronegativity than other non-metals.
Hydrogen has a lower electronegativity than other non-metals.
Covalent bonds are classed as polar if the bond is between atoms of elements having different electronegativities.
The term polar is used because the sharing of electrons in these bonds is unequal with the electron density being higher at the more electronegative atom. This atom has a partial negative charge (δ–) and the other atom in the bond has a partial positive charge (δ+).
Diatomic molecules (two atoms such as HF) are polar (have atoms with partial negative and positive charges) if the atoms are different because the electronegativities of the atoms will be different.
When comparing the polarities of diatomic molecules, the most polar one has the largest difference in electronegativities of the two atoms.