Chemistry 112
Chapter 8
Chemical Bonding and
Molecular Shapes
Mr. McIsaac
Carleton North High School
Electron Arrangement
(Energy Levels, Sublevels, Orbitals)
• Electrons travel around the nucleus at
certain distances, called energy levels.
• Inside each energy level, there are
sublevels; the number of sublevels is equal
the number of the energy level:
– 1st energy level has 1 sublevel (s)
– 2nd energy level has 2 sublevels (s, p)
– 3rd energy level has 3 sublevels (s, p, d)
– 4th energy level has 4 sublevels (s, p, d, f)
– 5th energy level has 5 sublevels (s, p, d, f, g)
Electron Arrangement (cont.)
• Inside each sublevel, there are orbitals –
specific regions/areas inside the e cloud where
individual e’s exist.
• An orbital may be empty, or may hold 1 or 2 e’s.
Any orbital can hold a maximum of 2 e’s.
• An outer level (valence level) can hold a
maximum of 8 e’s. So, an outer level has a
maximum of 4 orbitals.
Electron Arrangement (cont.)
• Stated another way, an outer level has a
maximum of 2 sublevels (s, p).
• An s sublevel has 1 orbital; a p sublevel has 3
orbitals. Total = 4 orbitals = 8 e’s (2 per orbital).
• Valence electrons exist in these outer 4 orbitals.
Filling The Outer Level
• As bonded elements:
– The first 4 e’s (1, 2, 3, 4) will singly/separately
occupy each of the outer 4 orbitals – the 1st in the s
orbital, and 2nd, 3rd, 4th in each of the 3 p orbitals.
– The next 4 e’s (5, 6, 7, 8) will pair up in each of the
outer orbitals – the s, and then the 3 p orbitals.
• As unbonded elements (FYI; we don’t worry about it):
– The first 2 e’s (1 and 2) will fill the s orbital
– The next 3 e’s (3, 4, 5) will singly/separately occupy
each of the 3 p orbitals.
– The next 3 e’s (6, 7, 8) will pair up in each of the 3 p
orbitals.
Lewis Electron Dot Diagrams
• In a Lewis Electron Dot Diagram for an
element, the symbol of the element represents
the nucleus and all the inner electrons, and the
4 sides around the symbol represents the 4
valence orbitals.
• Each of the above dot diagrams is equivalent –
any of the 4 sides is the same
Lewis Electron Dot Diagrams
• Electrons like to exist in pairs, and single e’s
bond/share with single e’s from other atoms.
• When two atoms share a pair of e’s, it is called
a bonded pair, shared pair, or covalent bond.
• Notice that when showing dot diagrams for
different elements forming a compound, it is
common to use dots for one element and x’s for
the other – it just makes it easier to follow.
VSEPR Theory
And Predicting Molecular Shapes
• Valence Shell Electron Pair Repulsion (VSEPR)
theory is the understanding that pairs of e’s will
repel each other and move as far apart from
each other as possible.
• Predicting molecular shapes and bond angles
can be done by drawing dot diagrams showing
the pairs of e’s (shared and unshared) around a
central atom.
5 Molecular
Shapes
From
Single Bonds
Double and Triple Bonds
• Adjacent atoms can share more than one
pair of electrons.
• Try O2, N2, CH2O, CHP
Summary: Predicting Molecular Shapes
• Draw the Lewis Dot Diagram for the
molecule to determine the number of
bonding and non-bonding electron pairs.
• Make sure all atoms are present.
• Cannot have any single e’s (dots/x’s) left.
• Only adjacent atoms can bond.
• E’s/dots from same atom cannot pair up.
• When determining the shape of a
molecule with multiple bonds, treat the
multiple bonds as if they were single
bonds (i.e. one bonding side or direction)