Chemical Bonding
The concept of electron configurations allowed chemists to explain why chemical
molecules are formed from the elements. In 1916 the American chemist Gilbert
Lewis proposed that atoms could achieve a noble gas electronic configuration by
gaining, losing or sharing electrons with other atoms. Since the noble gases (except
He) have 8 valence electrons his proposal is known as the octet rule.
The rule states that, except for hydrogen, an atom combines with other atoms to
form bonds in order to have 8 electrons in its valence (outermost) shell. If this is
not possible the atom would rather lose its valence electrons the same goal.
Lewis dot symbols are representations of the elements that give a dot for each
valence electron on the atoms
Examples for period 2 elements are
You can determine the number of valence electrons by looking at the periodic table.
Above each column you will find a number followed by an “A”. This number
corresponds to the number of valence electrons of each element in the column.
Construct Lewis structures for the following elements
Ga
P
Br
Ca
Si
Ionic Bonds
Ionic bonds usually form from the reaction of metals and non-metals and involve the
transfer of one or more electrons. Look at the sample chemical reaction below,
which shows the ionic bonding of Sodium.
2Na(s) + Cl2 (g) 2NaCl (s)
For the example given above show the Lewis structures for the Reactants in the
reaction above
Na
Cl
Now in the box below show the movement of electrons between Na and Cl, using an
arrow to show the movement of electron between the two elements.
Use Lewis dot symbols to show the transfer of electrons between the following
atoms, if needed add extra atoms to make each reactant stable
K and S
O and Ba
Sr + Se
Al + S
Mg + F
Covalent Bonds
These bonds usual occur during the reaction of non-metallic atoms and involve the
sharing of electrons to complete each atoms octet.
Some atoms are known as diatomic molecules because they are commonly found
bound to each other in pairs such as Fluorine.
How many valence electrons are there in F?
Total Valence number =
How many electrons will 2 atoms of Fluorine share in a diatomic molecule to
complete their octets Answer:_______
Use Lewis structures to show the sharing of electrons in the F2 (diatomic) molecule
The shared electrons form the chemical bond between the F atoms. The other 3
pairs of electrons on each of the F atoms are called Lone Pair Electrons and are not
involved in bonding.
Draw the Lewis Structure of water, H20 to show the bonding
Total # of valence electrons in H2O = _______
Total number of bonds formed ______________
Type of bond formed__________________________