Types of Bonding
There are three types of bonding – metallic, ionic, covalent molecular and covalent network.

Metallic Bonding
In metallic bonding, the outer electrons of metals are only weakly held so are able to drift away from the
atom to become what are called delocalised electrons. The delocalised electrons do not completely leave
the piece of metal. They form what is termed a ‘sea of electrons’. Atoms have equal numbers of protons
and electrons so, when the metal loses its outer electrons, it has more protons than electrons and
therefore becomes a positive ion. The electrostatic attraction between the positively charged metal ions
and the ‘sea of electrons’ is what holds the ions in the metal together. The metal ions line up in a regular
arrangement like a crystal. This regular 3D arrangement is called a lattice. However, there is no bond (force
of attraction) between a positive ion and the other positive ions around it. This is why metals are malleable
and ductile. Applying a force to a metal can move the positive ions around into new positions and the ‘sea
of electrons’ will follow the ions to their new position.

Ionic Bonding
Atoms like to have a full outer shell or exactly eight electrons in their outer shell because this makes the
atom more stable. Metal atoms have a small number of electrons in their outer shell (1, 2 or 3). They
obtain a full outer shell by losing these outer electrons to make the full shell below the outer shell. Nonmetal atoms have a large number of electrons in their outer shell (5, 6, or 7 for groups 5, 6 and 7).
Elements in groups 5, 6 and 7 obtain eight electrons in their outer shell by gaining 3, 2 or 1 electrons from
an another atom that likes to lose electrons. When sodium atoms (11 protons and 11 electrons) and
chlorine atoms (17 protons and 17 electrons) react together, the sodium loses its one outer electron to
make a sodium ion (11 protons and 10 electrons with 8 electrons in the outer shell) and the chlorine gains
the one electrons lost by sodium to make a chloride ion (17 protons and 18 electrons with 8 electrons in
the outer shell). The sodium ion has a charge of +1 and the chloride ion has a charge of -1. The sodium ions
and chloride ions arrange themselves with positive and negative ions next to each other in a 3D lattice. The
electrostatic attraction between the positive and negative ions is the bond that holds the crystal together.

Covalent Bonding
In covalent bonding, atoms are driven to obtain an outer shell with 8 electrons, a full outer shell or at least
no unpaired electrons because this increases stability. They do this by sharing electrons with other atoms.
A Lewis dot diagram is useful for representing covalent bonding. An alternative to Lewis dot diagrams is
structural formulas. Structural formulas use a straight line to represent a single covalent bond. One single
covalent bond means one shared pair of electrons. A double bond (two shared pairs of electrons) is
represented to two parallel lines and a triple bond (three shared pairs of electrons is represented by three
parallel lines.
The structural formula is easy to draw and is an aid to drawing Lewis dot diagrams. However, the structural
formula only shows shared electron pairs and not all electrons in the outer shell so is not totally equivalent
to a Lewis dot diagram.
With structural formulas, remember that carbon and silicon always form 4 bonds, hydrogen always forms 1
bond, group 7 elements almost always form 1 bond, oxygen and sulfur generally form 2 bonds and
nitrogen generally forms 3 bonds. This rule relates to the group in the Periodic Table.

Classifying Compounds by Their Type of Bonding
Type of Bonding
Metallic
Ionic
Covalent Molecular
Covalent Network
How to Identify
Contains only metals. Either a pure metal or an alloy.
A compound of a metal and a non-metal.
The metal may be replaced by a polyatomic cation such as ammonium (NH4+).
A compound of non-metals only other than the small number of covalent network
substances.
There are not many examples of substances with covalent network bonding.
Elemental silicon or carbon (diamond, graphite, Buckminsterfullerene). Silicon
dioxide (quartz a.k.a. sand). Boron nitride (BN) and silicon carbide (SiC).