Lewis notation uses dots and crosses to represent the valence
electrons on different atoms. The chemical symbol of the element is used to
represent the nucleus and the inner electrons of the atom. To determine which are the valence
electrons we look at the last energy level in the atom's electronic structure (Chapter
4). For example, chlorine's electronic structure can be written as:
\(1\text{s}^{2}2\text{s}^{2}2\text{p}^{6}3\text{s}^{2}3\text{p}^{5}\) or
\([\text{Ne}]3\text{s}^{2}3\text{p}^{5}\). The last energy level is the third one and it
contains 7 electrons. These are the valence electrons.
If we write the condensed electron configuration, then we can easily see the valence
electrons.
For example:
A hydrogen atom (one valence electron) would be represented like this:
A chlorine atom (seven valence electrons) would look like this:
A molecule of hydrogen chloride would be shown like this:
The dot and cross in between the two atoms, represent the pair of electrons that are shared in the
covalent bond.
Table 6.1 gives some further examples of Lewis
diagrams.
Iodine
\(\text{I}_{2}\)
Water
\(\text{H}_{2}\text{O}\)
Carbon dioxide
\(\text{CO}_{2}\)
Hydrogen cyanide
\(\text{HCN}\)
Table 6.1: Lewis diagrams for some simple molecules
For carbon dioxide, you can see how we represent a double bond in Lewis notation. As there are two
bonds between each oxygen atom and the carbon atom, two pairs of valence electrons link them.
Similarly, hydrogen cyanide shows how to represent a triple bond.
Lewis structures
Textbook Exercise 6.1
Represent each of the following atoms using Lewis notation:
beryllium
calcium
lithium
Solution not yet available.
Represent each of the following molecules using Lewis
notation:
bromine gas \((\text{Br}_{2})\)
carbon dioxide \((\text{CO}_{2})\)
Which of these two molecules contains a double bond?
Solution not yet available.
Two chemical reactions are described below.
Nitrogen and hydrogen react to form \(\text{NH}_{3}\)
Carbon and hydrogen bond to form a molecule of
\(\text{CH}_{4}\)
For each reaction, give:
the number of electrons in the outermost energy level
the Lewis structure of the product that is formed
the name of the product
Solution not yet available.
A chemical compound has the following Lewis notation:
How many valence electrons does element Y have?
What is the valency of element Y? (remember that the
valency of an atom is the number of chemical
bonds it can form.)
