LA.1.1 Bonding and Electronegativity
Bonding
A chemical bond is an attractive force between two atoms. This force is due to the electrons from
different atoms interacting with each other.
The electrons involved in bonding are called valence electrons. Valence
electrons are the electrons in outer shell. The electron configuration for magnesium is
2, 8, 2. The valence electrons are final 2.
Ionic Bonding
Covalent Bonding
Ionic bonding involves one atom accepting or
donating its valence electrons to another.
Covalent bonding involves atoms sharing its valence
electrons.
A single covalent bond is
formed when one electron is
donated by both atoms.
Figure 2 The covalent bonding in methane.
Figure 1 The ionic bonding in magnesium oxide (MgO).
The metal (Mg in the example above) donates its
valence electrons to a non-metal electron acceptor
(oxygen in the example above).
This bond is dominated by electrostatic effects i.e
opposite charges attracting.
A double bond is formed when
two electrons are donated by
both atoms.
Figure 3 The covalent bonding in dioxygen
which highlights the double bond formation.
This type of bond is dominated by orbital overlap
Small highly charged ions form stronger bonds than
larger low charged ions.
Similar sized orbitals form stronger bonds than
different sized orbitals.
Ionic bonding is commonly found within charged
molecules forming salts:
C-F > C-CL > C-Br > C-I
Look Up CLMETH, MBRMET10, MIMETH10
+
-
Figure 4 Ammonium carbamate ([NH4 ][CH2NO2 ] is an
example of an ionic compound.
Figure 5 Covalent bonding in methanol. This is an example of a
strong covalent bond as there is good overlap between the
similarly sized carbon and oxygen (both their valence electrons
are in 2p orbitals).
Ionic or Covalent?
The difference in electronegativity dominates whether a bond is going to be ionic or covalent. If the
difference in electronegativity is large, then it is likely the bond will be ionic. If it is small, then is likely
that bond will be covalent. A polar covalent bond is an intermediate between an ionic and a covalent
bond.
Electronegativity



Electronegativity is a measure of the
KEY Definition: The tendency of an
ability of an atom in a molecule to draw
atom or a functional group to attract a
bonding electrons to itself.
bonding pair of electrons (or electron
The most common way of measuring
density) towards itself.
electronegativity is by use of the Pauling
scale.
Fluorine (the most electronegative element) is assigned a value of 4.0, and values range
down to caesium and francium which are the least electronegative at 0.7.
Electronegativity increases across a period
Electronegativity
DECREASES
down a group
Bonding and Electronegativity
The character of the bond depends on the electronegativities of the atoms forming the bond.
Specifically, the difference in electronegativities.
Equal Electronegativity
This bond will be a purely
COVALENT bond:
A Slightly More
Electonegative than B
This bond will be a polar
COVALENT bond:
δ-
δ+
A Significantly more
Electronegative than B
This bond will be a IONIC
bond:
A-
B+
Breaking Bonds
Covalent bonds will have a tendency for HOMOLYTIC FISSION as the two bonding electrons
are equally distributed.
Polar bonds will have a tendency for HETEROLYTIC FISSION as the two bonding electrons
are drawn towards the more electronegative atom.