The Lewis representation allows us to visualize the chemical bonds between atoms. A chemical bond forms when two atoms share valence electrons. Chemical bonds can be represented by shared pairs of dots between the atoms in the Lewis representation.
Electronic Configuration
Key Points:
An atom has as many electron(s) as proton(s). Electrons are distributed in the different electron shells and subshells, filling them in order (Z ≤ 18): 1s 2s 2p 3s 3p
In an s subshell, a maximum of 2 electrons can be placed; in a p subshell, a maximum of 6 electrons.
Example: N (Z = 7) has the electronic configuration 1 s2 2 s2 2 p3
Definition
Valence Electrons
Valence electrons correspond to all the electrons in the outermost electron shell (the last to be filled), noted in bold in the example.
Lewis Representation
Key Points:
The Lewis representation uses chemical symbols to represent atoms. Atoms are represented by their chemical symbol, for example H for hydrogen, O for oxygen, C for carbon, etc.
Valence electrons are represented by dots or pairs of electrons around the symbols of the atoms.
Valence electrons are arranged so that each atom has a stable electronic configuration, meaning the outer electron shell is filled.
Geometric Representation
Key Points:
The geometry adopted by a molecule is the one in which the electron pairs (bonding and non-bonding) are as far apart as possible.
Let A: a given central atom.
n: the number of X atoms bonded to A
m: the number of non-bonding electron pairs E borne by A
Examples:
CH4 molecule of type AX4
NH3 molecule of type AX3E1
H2O molecule of type AX2E2
The table below summarizes the geometry of molecules of type AXnEm for n + m ≤ 4
