The Chemistry of
Titanium
1c – Bonding Types 2
Compounds
Learning Intentions
• To gain an understanding of how
electronegativity affects polarity of bonds
• To be able to identify Pure Co-valent, Polar Covalent and Ionic bonding from
electronegativities
• To be able to place molecules within the
bonding continuum
• To be able to relate molecular
shape/symmetry to polarity of molecules
Covalent Bonding
A covalent bond is a shared pair of electrons
Both nuclei try to pull the electrons towards themselves
electrostatically attracted to the positive nuclei of two
atoms.
+
-
+
Theaatoms
achieve
a stable
This is like
tug-of-war
where
bothouter
sideselectron
are pulling on
arrangement (a noble
gas arrangement)
by sharing
the same
object.
electrons.
It creates a strong bond
between the two atoms.
Covalent Bonding
Picture a tug-of-war:
If both teams pull with the same force the mid-point of the
rope will not move.
Pure Covalent Bond
H
e
e
H
This even sharing of the rope can be compared to a pure
covalent bond, where the bonding pair of electrons are
held at the mid-point between the nuclei of the bonding
atoms.
Covalent Bonding
What if it was an uneven tug-of-war?
The team on the right are far stronger, so will pull the rope
harder and the mid-point of the rope will move to the
right.
Polar Covalent Bonding
There
A
polariscovalent
a small difference
bond has some
between
ionicthe
character.
electronegativities of both atoms and
the bonding electrons are pulled more closely to the more electronegative
atom.
δ+
P
δe
Cl
e
2.2
H
e
e
3.0
δ+
H
e
Cl
P
Electronegativities
e
Increasing ionic character
δ-
Polar Covalent Bond
A polar covalent bond is a bond formed when the shared
pair of electrons in a covalent bond are not shared equally.
This is due to different elements having different
electronegativities.
Polar Covalent Bond
e.g. Hydrogen Iodide
δ+
H
δe
e
I
If hydrogen iodide contained a pure covalent bond, the
This
makeswould
iodinebe
slightly
negative
hydrogen
slightly
electrons
shared
equallyand
as shown
above.
positive. This is known as a dipole.
However, iodine has a higher electronegativity and pulls
the bonding electrons towards itself
(winning the tug-of-war)
Polar Covalent Bond
In general, the electrons in a covalent bond are not equally
shared.
e.g.
C
2.5
δ+
δ-
Cl
3.0
Electronegativities
δ- indicates where the bonding electrons are most likely to
be found.
Polar Covalent Bond
Consider the polarities of the following bonds:
Difference
Electronegativities
Bond
C
Cl
2.5
3.0
0.5
P
H
2.2
2.2
0
O
H
3.5
2.1
1.4
P
H
δ+
C
Cl
δ-
δ-
O
H
δ+
Increasing Polarity
Complete a similar table for C-N, C-O and P-F bonds.
Polar-Polar Attractions
The differing electronegativities of different atoms in a
molecule and the spatial arrangement of polar covalent bonds
can cause a molecule to form a permanent dipole.
-
+
No permanent dipole
Symmetrical molecule
Permanent dipole
Asymmetrical molecule
+
-
-
4 polar covalent C-Cl bonds in CCl4
tetrahedral shape
NON-POLAR molecule
e.g. also CO2
-
-
3 polar covalent C–Cl bonds and
1 polar covalent C-H bond in CHCl3
POLAR molecule
e.g. also H2O
Polar molecules and permanent
dipoles
Both propanone and butane have the same formula mass of 58
however, butane boils at – 1 oC while propanone boils at 56oC
Propanone is a polar molecule as it has a permanent dipole, so has polar-polar
attraction as well as Van der Waals’ forces between molecules.
H
H
C
H
-
O
H
C
C
+
H
b.p. 56 o C
H
Butane has no permanent dipoles, so only Van der Waals forces
between molecules. So has a lower boiling point.
H
H C
H
H
C
H
H
C
H
H
C H
H
b.p. -1 o C
Polar Molecules
A liquid that substances dissolves in is called a SOLVENT.
Solvents can be either polar or non-polar molecules.
Immiscible liquids do not mix, e.g. oil and water, however,
non-polar liquids are miscible with each other.
Polar solvents will usually dissolve polar molecules.
Non-polar solvents will usually dissolve non-polar molecules.
Water is a polar molecule so it is a polar solvent.
+
-+
Ionic Bonds
Ionic bonds are formed between atoms with a large difference in
electronegativities. They are often (though not always) between metals and
non-metals.
For example, in potassium bromide, the difference in electronegativities is so
large that potassium will lose an electron and form a positive ion.
Bromine gains this electron and forms a negative ion. The ionic bond is the
electrostatic force of attraction between a positive and negative ion.
Reacting Elements:
K
e-
Br
Electron Arrangement:
2,8,8,1
2,8,7
During Reaction:
loses 1e-
gains 1etransfer of an
electron
Ions Formed:
New Electron Arrangement:
K
2,8,8
+
Br
2,8,8
-
The electrostatic force of attraction between the oppositely
charged ions is called the ionic bond
K
+
Br
Ionic compounds form a LATTICE STRUCTURE. Millions of oppositely
charged ions are held together in a very stable arrangement.
-
Ionic Bond
An
ionic
bond
existsofwhen
the difference
in electronegativities
so great
that
There
is no
sharing
the electrons
and oppositely
charged ionsis are
formed.
the movement of the bonding electrons between the two atoms is complete.
Li
+
F
e
e
1.0
H
e
e
H
4.0
Electronegativities
δ+
e
P
e
Increasing ionic character
δCl
Li
+
F
-
Bonding Continuum
Pure Covalent
Bond
Polar
Covalent
Bond
Ionic Bond
To judge the type of bonding in any particular compound it is more important
to look at the properties it exhibits rather than simply the names of the
elements involved.
H
e
e
δ+
H
P
e
e
Increasing ionic character
δCl
Li
+
F
-
Electronegativity is useful at predicting how electrons will be
shared. The Pauling scale is used for electronegativity values
The greater the difference in electronegativity the greater the
polarity between two bonding atoms and the more ionic in
character.
Increasing difference in electronegativity
Non-polar
slightly polar covalent
Equal sharing
of electrons
4.0
F
F4.0
very polar covalent ionic
Increasing unequal
sharing of electrons
3.5
O
H 2.1
Transfer of
electrons
0.9
Li
F 4.0