Investigating Covalent Bonds
Covalent bonds are formed when atoms share electrons, one from each
atom in a single bond, to form electron pairs, usually making their
outermost shells up to eight electrons by this means. This would make
them more stable, less reactive and an electronic structure like a
They are most frequently formed between pairs of non-metallic
elements. Non-metallic elements usually have from four to eight
electrons in their outermost shells, the so-called valency electrons,
which are used for chemical bonding. In any given “full” shell of
eight electrons, the electrons occur in four pairs, but in incomplete
shells, the electrons exist singly where possible.
Sometimes, atoms of elements form covalent bonds with other atoms of
the same element. Thus two chlorine atoms form the chlorine molecule,
Cl2, by sharing their unpaired electrons. In the case of oxygen (O2),
there are two unpaired valency electrons in each atom, so that two
electron-pair bonds are formed between the two atoms to complete their
octet of electrons, a double bond.
Covalent bonds can also be formed in such a way as to form a giant
molecule, such as happens in diamond. Here, each of the four valency
electrons of a carbon atom is shared with one of the valency electrons
of another carbon atom, so that every carbon atom in the structure has
four different carbon atoms bonded to it.
In simple molecules, the molecules are held together by strong
covalent bonds, but the bonds between different molecules are
relatively weak, and therefore easily broken. Many compounds
containing covalent bonds, therefore, are liquids or gases at room
temperature, although at lower temperatures they form crystalline
solids; those that are solids at room temperature have relatively low
melting and boiling points.
These compounds are frequently insoluble in water, as the mechanism
for dissolving described for ionic compounds cannot occur. However,
water is also capable of dissolving covalent compounds which form
hydrogen bonds, because instead of the ionic attachment, the water
molecules can attach themselves to the molecules of the covalent
compounds, with a similar result.
Ionic bonds are formed through the electrostatic attraction between
two oppositely charged ions. This type of bond normally occurs between
metallic and non-metallic elements. Metals typically have few valency
electrons, and occur in groups I, II, and III of the periodic table;