Electronegativity
When two atoms are joined by a covalent bond, the electrons of that bond are shared — but not always shared evenly.
Electronegativity
The ability of an atom to attract the electrons of a bond towards itself, when it is bonded to another atom by a covalent bond.
An atom of higher electronegativity pulls harder on the bonding electrons than an atom of lower electronegativity does. You will meet this idea again under chemical bonding.
The Pauling scale
Several scales exist for expressing electronegativity; the one used here is the Pauling scale. On it, the element of highest electronegativity is fluorine.
| Period | I | II | III | IV | V | VI | VII | VIII / 0 |
|---|---|---|---|---|---|---|---|---|
| 1 | H 2.1 | He — | ||||||
| 2 | Li 1.0 | Be 1.5 | B 2.0 | C 2.5 | N 3.0 | O 3.5 | F 4.0 | Ne — |
| 3 | Na 0.9 | Mg 1.2 | Al 1.5 | Si 1.8 | P 2.1 | S 2.5 | Cl 3.0 | Ar — |
| 4 | K 0.8 | Ca 1.0 |
Figure 3.9 — electronegativity of the elements with atomic numbers 1 to 20, on the Pauling scale.
Be careful
The noble gases have no value on the scale. They show little tendency to form chemical bonds at all — and with no bond, there are no bonding electrons to attract.