Practice Sheet
Electron Dot (Lewis) Structures
A Lewis or Electron Dot Structure is a convenient representation of the valence electrons in an atom.
An electron dot structure for an atom is simply the symbol for the element, surrounded by a number of dots
equal to the number of valence electrons.
Avoid a common mistake: the dots represent valence electrons only, so make sure you use only the number
of dots corresponding to the number of valence electrons.
Examples:
...
Al
..
..
C
.
.
P
.
..
.
.
.
..
.
.
.
Kr
..
Ca
.
Na
•Draw lewis dot structures for an atom of each of following elements:
1. K
2. Si
3. Ar
4. As
Covalent Bonds
An atom can also achieve a noble gas configuration by sharing electrons with other atoms. When two non-
metals combine, they typically share electrons in covalent bonds and form what are know as covalent compounds.
We can draw Lewis Electron Dot Diagrams for covalent molecules to determine what type of bonds the
molecules form.
For example, consider two hydrogen atoms. Each one has one valence electron. However, both hydrogens
would like to have two electrons, to obtain the same configuration as [He]. To do this, each H atom shares
an electron with the other, forming a covalent bond. In H2, each H atom has 2 electrons.
each H has 1 e−
and wants 1 more shared pairs can
be represented as
lines between atoms
a hydrogen
molecule
(diatomic = 2 atoms)
H H H2
+
H H H H
H’s share e−’s
forming a covalent
bond
. . .
.
Here’s another example, this time for chlorine. A Cl atom has 7 valence electrons, so it needs 1 more to
achieve an octet (8 electrons).
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
..
.
.
..
.
.
.
forming a covalent
2
molecule
and wants 1 more
each Cl has 7 e−
Cl
a chlorine
+
Cl Cl Cl Cl ClCl
. .
each Cl shares 1 e−’s
bond consisting of
2 electrons the shared electron pair
is represented as a line
Each chlorine now has 8 electrons, because you can count the shared ones:
