Chemical Bonding
Ch. 8
IONIC
• Atoms in ionic compounds transfer
electrons when they bond and become
charged.
• This occurs when nonmetals bond with
metals.
COVALENT
• Covalent bonds – atoms held together
by sharing electrons.
• Bonding allows atoms to fill their
energy level and become more stable.
• Sharing electrons form covalent bonds
and occurs when nonmetals bond with
nonmetals. Each bond shares 2
electrons.
• Atoms share electrons in covalent
bonds to attain a noble-gas electron
configuration.
• Valence electrons are electrons located
on the outer energy level. We can
represent the valence electrons with
dots.
• Atoms usually acquire a total of 8
electrons in the outer level. This is
called the octet rule.
• H and He, need 2 electrons to fill their
valence.
• All other elements need 8 electrons to
fill their valence.
• For a noble gas, the outermost energy
level for the electrons is filled.
• In forming the molecule HF, the F atom
attains the electron configuration of Ne.
• Molecule – atoms joined together by
covalent bonds
• Atoms in molecules share electrons
when they bond.
• NH3 is a covalent molecule.
• Diatomic molecule – consists of 2
atoms
• Br.I.N.Cl.H.O.F.
• Chlorine (Cl) exists as a diatomic
molecule
• The diatomic molecule F2 contains a
single covalent bond.
Electron Dots and Bonding
• Lewis structures use electron-dot
diagrams to show how electrons are
arranged in atoms.
• Electrons are represented by dots.
• A pair of electrons may be represented
by 2 dots or a dash.
• The electron dot structure for H2 is H:H
or H―H
• The pairs of valence electrons that do
not participate in bonding in diatomic
oxygen molecules are called unshared
pairs.
• Use NASB to draw dot diagrams.
• N – electrons needed to fill valence (8
or 2)
• A- electrons available in atom
• S – electrons shared = N – A
• B – formed bonds (S 2)
• In Cl2, the total number of unshared pairs of
electrons is 6.
• Cl
+
Cl

Cl―Cl
or Cl:Cl
• The diatomic molecule N2 contains a triple
covalent bond.
• N
+ N 
N≡N
or
N⋮⋮N
• In the N2 molecule, there is only one
unshared pair of electrons in each nitrogen
atom.
• The HI molecule contains only one single covalent
bond.
•
H•
+
I

H―I
or
H:I
• There are 4 single covalent bonds in a molecule of
CH4.
H
H
•
C
+ 4H•
 H:C: H
or
H C H
H
H
• There are 2 double covalent bonds in a molecule of
CO2.
•
C
2 O

O═C═O
or
O::C::O
• Carbon monoxide has a triple covalent bond.
C O  C≡O
OR
C⋮⋮O
Bonding Theories
• According to VSEPR theory, molecules
adjust their shapes to keep pairs of
valence electrons as far apart as
possible.
• VSEPR –
– Valence Shell Electron Pair Repulsion
• A stereoactive set is a shared pair or an
unshared pair of electrons around the
central atom.
• The shape of a molecule of CO2 is
linear.
• The shape of a molecule of HCN is
linear.
• The shape of a molecule of CH4 is
tetrahedral.
• The shape of a molecule of NH3 is
trigonal pyramidal.
• The shape of a molecule of H2O is bent.
• According to VSEPR theory repulsive
forces between unshared pairs of
electrons causes water molecules to
have their shape.
Bond angle =
109.5 degrees
Example: CH4
Bond angle =
106.5 degrees
Example: NH3
Bond angle =
104.5 degrees
Example: H2O
Bond angle =
120 degrees
Example: CO32-
Bond angle =
118.6 degrees
Example: O3
Bond angle =
180 degrees
Example: CO2
Polar Bonds
• In a polar covalent bond, electrons are
shared unequally. Some atoms
(elements) are more electronegative
and attract electrons more. They will
gain a slightly negative charge.
• The electronegativity difference
determines the type of bond.
• HF contains a polar covalent bond.
• F forms a more polar bond with H than
Cl, Br, or I.
• An ionic bond would be expected in a
molecule of LiF.
• Intermolecular forces – forces between
2 molecules
• Van der Waals forces - 2 weakest
attractions between molecules
• Dipole interactions – polar molecules
attracted to one another
• Dispersion forces – caused by the
motion of electrons
• Hydrogen bonds – strongest
intermolecular forces
• Hydrogen covalently bonded to a very
electronegative atom is also bonded to
an unshared electron pair of another
electronegative atom.
• H2O is a polar molecule.
• 2 H• +
O 
:O:H
•
H
• http://enstrophy.colorado.edu/~mohseni/A
SEN5519Spring2004/TypesOfChemicalBo
nds1.html