1) Chemical bonds form when atoms overlap their orbitals to achieve stable noble gas configurations. This increases stability as atoms form ionic or covalent bonds. 2) Metallic bonding occurs via a "sea of electrons" model where mobile electrons are shared between rigid positive ions. This explains properties like conductivity and malleability. 3) There are various types of bonds including ionic formed between metals and nonmetals, and covalent including polar, nonpolar, and coordinate bonds formed by electron sharing or donation.

1. Chemical Bonding
Chemical Bonding-
By Aditya Abeysinghe
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2. Why are bonds formed?
Many elements and ions in nature are unstable
and sometimes they are highly reactive. However
any element or ion tend to increase their stability
by achieving the noble gas configurations.
For example, a sodium atom which has a valence
electron may bind with an electron deficient
chlorine atom to form sodium chloride. Thus the
sodium atom will achieve the noble gas
configuration and the chlorine atom will achieve
the noble gas configuration of argon and be stable.
Chemical Bonding-
By Aditya Abeysinghe
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3. Proof that formation of bonds make
the participant atoms stable
1. Most atoms in nature do not exist as ‘free’ atoms
but as compounds.
2. Emission of energy when bonds are formed and
the absorption of energy in the creation of
bonds.(According to the Gibb’s equation any
element becomes more stable when it possesses
less energy and is of high disorder)
3. Most rare gases are reluctant to form
compounds(However, some compounds of xenon
and argon have already being discovered)
Chemical Bonding-
By Aditya Abeysinghe
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4. Overlapping
When two orbitals are ‘on each other’ overlapping occurs.
However the percentage of overlapping changes depending on the
type of orbital.
For example the overlapping of two s orbitals is considered fully
overlapped since the percentage overlapped remains constant
regardless of the direction.(due to the spherical shape of the
orbitals)
In contrast, the overlapping of other orbitals such as p, d, and f
orbitals change because of their shape.
The overlapping
percentage remains
constant in s orbitals
regardless of direction
The
overlapping
percentage of p
orbitals
changes
according to
the direction in
which they
overlapChemical Bonding-
By Aditya Abeysinghe
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5. What is a bond?
A bond is the process by which two orbitals of
the two atoms overlap to form a molecular
orbital and produce a chemical connection
between the two atoms.
The bond is caused by the electrostatic force of
attraction between two oppositely charged
poles.
Chemical Bonding-
By Aditya Abeysinghe
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6. Types of bonds
Type of bond
(Primary Bonds)
Covalent bonds
Polar
Non-polar
Coordinate
Ionic or
electrovalent
bonds
Metallic bonds
Chemical Bonding-
By Aditya Abeysinghe
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7. Co-valent bonds
(Co+ Valent bonding)
Covalent bonds are bonds formed by sharing electrons
between the participating atoms. Here overlapping of two or
more orbitals produce molecular orbital(s) and form the bond
as a whole.
As mentioned earlier there are three types of bond by physical
nature
1. Non-polar covalent bonds
2. Polar covalent bonds
3. Coordinate covalent bonds
Covalent bonds can also be classified by the no. of bonds
existing between any two bonded atoms as
1. Single bond covalent formation
2. Double bond covalent formation
3. Triple bond covalent formation Chemical Bonding-
By Aditya Abeysinghe
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8. Non polar covalent bonding
In non-polar covalent bonding,
1. The electronegativity difference between the
atoms is less than 0.4 and sometimes 0.
2. The dipole moment of such bonds may be
negligible.
E. g: CH4 The electronegativity
of the C-H bond is
0.35. However the
polarity of any three C-
H bonds is neutralized
by the other bond due
to the tetrahedral
shape of methane. Thus the
molecule as a whole is non
polar
Chemical Bonding-
By Aditya Abeysinghe
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9. Polar covalent bonding
Polar bonding results when two different non-
metals unequally share electrons between
them.
Polar covalent bonds usually exist in molecules
where
1. There is an imbalance of the electro
negativities in a molecule as a whole.
2. The electro negativity between the atoms in
a specific bond lies between 0.4 and 1.6.
Chemical Bonding-
By Aditya Abeysinghe
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10. E. g: When one hydrogen of methane is
being replaced by a hydroxyl radical(-OH)
the formation of methanol will result in a
non-polar molecule due to the imbalance
or the residue of the electro negativities in
the molecule as a whole
Methanol(CH3- OH)
Chemical Bonding-
By Aditya Abeysinghe
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11. Coordinate covalent bonding
(Dative covalent/ Dipolar bond)
Coordinate covalent bonds result when both
electrons in a specific bond is ‘gifted’ by a donor(by a
single element unlike the sharing of electrons
provided by both elements in the bond)
A dipolar bond is formed when a Lewis base donates
a pair of electrons to a Lewis acid(for a detailed
description of Lewis acids and Lewis bases see the
next slides).
For example the Ammonium ion is formed by
donating a pair of electrons to the electron deficient
Hydrogen ion by the Ammonium compound.
Chemical Bonding-
By Aditya Abeysinghe
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12. + [H]+
NH3 + H+ = NH4
+
Similarly Boron Tetraflouride is formed when the electron deficient
Boron Tri fluoride atom gains a pair of electrons from a donor fluoride
ion.
BF3 + F- = BF4
- .
Finally not only ions can act as electron donors or receptors but also
compounds.
For example the following compound is formed by the donation of a
pair of electrons from a ammonia compound to a boron trifluoride
compound.
Chemical Bonding-
By Aditya Abeysinghe
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13. NH . B
F
+
Chemical Bonding-
By Aditya Abeysinghe
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14. Lewis acid
A Lewis acid is an electron pair acceptor.
A Lewis acid may be formed by
1. By compounds in which central atom is
electron deficient
2. When multiple bonds exist between different
atoms
3. Atoms having sextet configuration.
4. By compounds containing a central atom with
an unfilled d- orbital.
E. g: Various metal cations, such as Mg2+ and metal
compounds such as AlCl3 are Lewis acids because
they have unfilled valence orbitals.
Chemical Bonding-
By Aditya Abeysinghe
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15. Lewis base
Lewis base is a compound with a pair of non
bonding electrons.
Thus H2O with its two pairs of non bonding
electrons on oxygen acts as a Lewis base by
donating an electron pair to an H+ thus forming
the hydronium ion, H3O+ .
Lewis bases can also be formed in similar methods as
that in Lewis acid formation. Chemical Bonding-
By Aditya Abeysinghe
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16. Ionic bonding
Ionic bonding usually occurs when a bond is formed by two
or more elements with electro negativity difference of 1.7
or more.
Ionic bonds are also called electrovalent bonds since the
two charges in any ionic bond have electrostatic properties
and a valency unlike that in any covalent compound.
In 1916, W. Cosol mentioned that ‘ atoms tend to achieve
the nearest noble gas electronic configuration when
participating in a chemical reaction’.
According to his theory, NaCl may be formed as follows:
Na- [Ne] 3s1 Na+-[Ne]
Cl- [Ne] 3s2 3p5 Cl–- [Ar]
NaCl
Chemical Bonding-
By Aditya Abeysinghe
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17. Electro-valency
Electro-valency is the process by which one or
more electrons are drifted between atoms and
result in the valency of an element.
The magnitude of the valency of an atom
depends upon the no. of electrons received or
donated in the process of electro-valency.
For example Mg2+ means that the magnesium
atom has donated two electrons either to a
recipient atom/compound or to an aqueous
solution. Also N3- means that nitrogen has either
gained three electrons from a donor ion/
compound or from an aqueous solution.
Chemical Bonding-
By Aditya Abeysinghe
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18. Characteristics of metals
1. Luster and reflection of incident light
2. High electrical and thermal conductivity
properties
3. High density
4. Malleability and elasticity
5. High melting and boiling points and also high
evaporation heats
6. Photoelectric effect
7. Formation of cations/positive ions in chemical
reactions
Chemical Bonding-
By Aditya Abeysinghe
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19. Drude and Lorentz theory
The model proposed by Drude was developed
by Lorentz and stated a new theory stemming
away from the structures of covalent and ionic
bonding.
The model states that a metal is composed of a
rigid positive ion lattice and the electrons in
that lattice do not form any attractions with the
positive ions and exist as a ‘cloud’ covering the
lattice.
Chemical Bonding-
By Aditya Abeysinghe
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20. Explaining the metallic bonding
using the hypotheses of Drude
1. Electrons which are at a lower level may promote to a
higher level when given energy to the atom. On
retuning to a lower energy level the energy is emitted
mainly as heat and light. Thus luster is visible to be
reflected over a specific metallic surface when
exposed to a light or radiation source.
2. The availability of free electrons makes it easier for
electrical and thermal conductions throughout the
metal. In contrast, due to the sharing of electrons in a
covalent bond tight attractions between bonding
atoms make its electron mobility extremely low. Thus
metals transfer the heat and electricity through
motion and vibration of electrons within the metal.
Chemical Bonding-
By Aditya Abeysinghe
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21. 3. High density of the metal may be due to
the close of electrons and the positive charges
within the metal.
4. Malleability and elasticity
As shown in the next page if we pull
opposite sides along A-B of a metal and of an
ionic compound, the metallic bond forms
attractive forces while the ionic compound
forms repulsive forces.
Chemical Bonding-
By Aditya Abeysinghe
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22. Metallic Compound
Ionic Compound
A B
Chemical Bonding- By Aditya Abeysinghe
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23. Covalent compounds too break up when applied with
stress due to weak intermolecular forces
E.g.: S, I, Naphthalene
However, giant covalent molecules like diamond do not
break easily. If broken, they do not form small sheets or
rods as in the case of metals
Due to the increase in the no. of mobility electrons
in a given area, the density of alkaline earth metals
(Mg, Be) is greater than that of alkaline metals
(Li, Na).
Chemical Bonding-
By Aditya Abeysinghe
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24. 5. High melting, boiling points and evaporation
heats can be described in a similar way to that of
the high density.
Similarly the photoelectric effect can be explained
by the luster given off by a metal due to the
incidence of light.
6. Formation of positive ions in a chemical
reaction
Due to the presence of high mobility electrons
the metal may tend to release one or more
electrons to a recipient element to make positive
ions equal in charge to the no. of electrons
released to make the ion.
Chemical Bonding-
By Aditya Abeysinghe
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25. For more information about the
intermolecular attractions and
other information on chemical
bonding visit the presentation
‘Chemical Bonding-2
By Aditya Abeysinghe’
Chemical Bonding-
By Aditya Abeysinghe
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