Covalent Bonding
Name: __________________________________ Form: ______________
Molecules are substances made up of 1 or more non-metal atoms bonded together. The atoms bond by
sharing electrons so that their outer shells (also called “valence” shells) are full. This bonding through
the sharing of electrons is called “Covalent Bonding”.
Eg. Water (H2O). Each oxygen atom has 6 electrons in its outer shell, but is
more stable if it acquires two more to “complete” the shell to eight electrons.
Hydrogen atoms have only one outer-shell electron. Each hydrogen atom
shares its electron with the oxygen atom which, in turn, shares one electron
with each hydrogen atom. The number of electrons in oxygen’s outer shell
increases to eight, and the number of electrons in the hydrogen atom’s outer
shell goes to two.
Therefore, all the outer shells are full and the molecule is stable.
The sharing of a single pair of electrons is called a single bond.
A. ELECTRON-DOT DIAGRAMS
Using these so-called “electron-dot diagrams”, draw the structures of
(a) methane (CH4)
(b) hydrogen fluoride (HF)
(c) ammonia (NH3)
(d) Hydrogen gas (H2)
(e) hydrogen peroxide (H2O2) (Hint: HOOH)
(f) chloromethane (CH3Cl)
(g) methanol (CH3OH)
(h) ethane (C2H6, but also written CH3CH3)
(i) hydrazine (N2H4)
Quite often, atoms share more than one electron. If they share two electrons each, it is called a double
bond; if three, a triple bond.
Draw the electron-dot diagram for
(j) oxygen gas (O2)
(k) carbon dioxide gas (CO2)
(l) ethene (also called ethylene) (C2H4, but also written CH2CH2)
(m) diazine (N2H2)
(n) Nitrogen gas (N2)
(o) ethyne (also called acetylene) (C2H2)
B.
STRUCTURAL DIAGRAMS
 A structural diagram represents each pair of valence electrons with a line,
instead of showing every outer-shell electron. The structural diagram for water
looks like the diagram at right.
 In a bond, one electron comes from each of the two atoms that are bonded.
 Structural diagrams only show the valence electrons.
 Any other valence-shell electrons within the molecule are also drawn as lines, even if they aren’t
being shared.
 Double bonds are drawn with two lines (=), and triple bonds with three lines (≡).
Next to each molecule you drew above, draw its structural diagram.