Covalent Bonds
A second type of bond is called a covalent bond. The prefix co- refers to being together.
Think of words like cooperate, corporation, and community. In this type of bonding electrons
are shared between the atoms in the
compound. Look at the image of the 2
fluorine atoms. When they come together,
the sharing of an valence electron with
each other completes the outer energy
levels of each atom. Usually the shared
pair of electrons is shown with a line representing the bond. If the atoms would lose one
electron to the other, the one giving up electrons would not have a fill outer energy level.
Elements in group 4A will form covalent bonds. Matter of fact, the element carbon is
found in more compounds than any other element due to its unique ability to share electrons.
Organic chemistry is a branch of chemistry dedicated to studying compounds that contain
carbon. If two nonmetals are bonded together, it is often a covalent bond holding them
together. Nonmetals are found in groups 4A, 5A , 6A and 7A, but also include hydrogen.
Elements that form covalent bonds have high electronegativities. Electronegativity refers to
the amount of energy needed to remove electrons. We graphed electronegativities at the
beginning of this unit. Nonmetals have high electronegativity, therefore form covalent bonds.
It is worth mentioning at this point 2 groups of molecules that are held together by
covalent bonds. They are diatomic molecules and polyatomic ions. We will be studying these
again later on. LEARN THEM! Lots of mistakes will happen later if you don’t know them.
Diatomic molecules are pairs of the same element held together by covalent bonds. Seven
elements will do this. They are: hydrogen (H2), oxygen (O2), chlorine (Cl2), fluorine (F2), nitrogen
(N2), iodine (I2), and bromine (Br2). These seven will never be alone- they will either be paired
up and held together with a covalent bond or in a compound. Polyatomic ions (poly = many;
atomic = atoms) are ions composed of more than 1 type of atom that are held together by
covalent bonds.
The diagram shows the polyatomic ion
sulfate (SO4-2). The 5 atoms are sharing their
valence electrons. As the counts show, the
group needs to 2 more electrons to fill all
the outer energy levels. It will gain those 2
electrons from the atom(s) that it will form a
compound with.
Later you will receive a chart with many of
these on it, so you do not need to memorize these. However, you will need to recognize them
in a compound. See the table for a few examples. Do notice what types of elements make up
all of the polyatomic ions- they are all nonmetals. When polyatomic ions are found in a
compound with a metal, an ionic bond can hold the polyatomic ion to the metal. So it is
possible to have more than one type of bond in a molecule.
Covalent bonds are weaker. Since they are weaker, these compounds have lower
melting points and produce more odors. Since there are no ions present, the compound will
not conduct electricity, not even when dissolved.