Lewis Theory

In 1916, American scientist Lewis proposed that when atoms combine with each other, there is a tendency to form a rare gas electronic configuration.
When atoms of an element with poor electronegativity form a bond, they can share electron pairs to achieve the electronic configuration of a rare gas
.

In the H ₂ molecule, two H atoms share a pair of electrons, so that each H atom can reach the 2-electron stable structure of the He atom, and a covalent bond is formed between the two H atoms; in the H ₂ O molecule, O atom and 2 H atoms each share a pair of electrons, H atom and O atom both reach the stable electronic configuration of noble gas, O atom and 2 H atoms each form a covalent bond
.

When drawing the Lewis structure, use small black dots to represent electrons, such as

For convenience, a short line is usually used to represent a shared pair of electrons, which means that a single bond is formed; two short lines are used to represent two pairs of electrons shared to form a double bond; and three short lines are used to represent three pairs of electrons to form a triple bond
.

[Example 6-2] Give the Lewis structural formulas of the following molecules or ions, and use short lines to indicate shared electron pairs
.

H ₂ , O ₂ , N ₂ , OH ^- , NO ⁺ , H ₂ O, NH2 _.