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Carbon Compounds
Chemical Bonding
Note Set 1b
Quantum Mechanics & Bonding
Schrödinger & others working in the early 20
th
century
recognized that electrons can be treated mathematically
as waves.
Schrödinger developed an equation for a wave function,
psi (Ψ) that mathematically describes an electron based
on its energy level in an atom.
Psi-squared (Ψ
2
) provides the probability of finding an
electron in a given region of space.
From a physical standpoint, Ψ
2
can be used to create an
electron probability map describing the region of space
where an electron in a given orbital can be found some
percentage of the time (usually 90-95%).
QM – Electron Probability Maps – s orbitals QM – Electron Probability Maps – p orbitals
Atomic Orbitals
An atomic orbital describes a region of space
where up to two electrons in an atom are likely to
be found.
Because atomic orbitals arise from the wave-like
motion of electrons, we can apply wave
properties to describe them.
Like a wave, AOs have + and – regions and
nodes.
Atomic Orbitals
Consider a transverse wave (as on a lake):
Regions of the wave are above (+) or below (–) the level
of the lake.
At some points, the wave is equal to the average level –
this point is a node.
VSEPR Table Handout
- Introduction to VSEPR
- The VSEPR Table should serve as a guide for how
to reason out shapes and bond angles. After a little
practice, you should not need to use the table.
- See the website for additional copies of the handout
provided in lecture.
Electron Dot
Structure
Total # of
ELECTRON
Regions
of
BONDING
Regions
of
LONE
PAIRS
Hybrid-
ization
Electron Arrangement SHAPE
Bond
Angle(s)
Sketch
2 electron regions - sp hybridization
Consider BeH
2
DRAW.
Draw the Lewis dot structure.
Both of the valence electrons from Be form
bonds.
However, in the electron configuration and in the
Aufbau diagram for Be, we see that both of the
valence electrons are already paired:
Be = 1s
2
2s
2
nd
E level:
s p p p
2 electron regions - sp hybridization
In order for Be to form two covalent bonds, it must
have two unpaired electrons.
One electron must be promoted to the 2p sublevel.
nd
E level:
However, an s orbital & p orbital will not allow for the
linear shape experimentally observed for the BeH
2
molecule.
The s & p orbitals hybridize to create two equivalent
sp orbitals that can take on a linear arrangement:
Hybridized 2
nd
E level:
s p p p
sp sp p p
Mixing of Atomic Orbitals - sp hybridization
BeH
2
Molecule
H 1s orbital
Be sp hybrid
orbitals
BeH
2
is a LINEAR molecule.
Be H H
sp sp p p
s s
1s orbital from
one H atom
1s orbital from a
second H atom
Be Hybridized 2
nd
E level:
3 electron regions - sp
2
hybridization
Consider BH
3
Draw the electron dot structure.
In BH 3
, boron needs 3 unpaired electrons to make three
bonds to hydrogens.
However, in the electron configuration and in the Aufbau
diagram for Be, we again see that two of the valence
electrons are already paired. DRAW.
Experimental evidence shows 3 equivalent bonds and a
planar molecule with120º bond angles.
3 electron regions - sp
2
hybridization
B = 1s
2
2s
2
2p
1
nd
E level:
s p p p
sp
3
hybridization in CH
4
s p p p
sp
3
sp
3
sp
3
sp
3
native atomic orbitals:
hybridized orbitals:
- Promotion
- Hybridization
Hybridization – sp
3
VSEPR & sp
3
Hybridization –
Bonding in Methane: sp
3
hybridization & orbital overlap
Orbital Overlap Diagram:
Methane
VSEPR – 4 electron regions - sp
3
hybridization
VSEPR – Valence Shell Electron Pair Repulsion
4 electron regions (from the 4 hybrid orbitals) à
TETRAHEDRAL electron arrangement
SHAPES (based on bonds & lone pairs):
Hybridization & VSEPR - General
One hybrid orbital is needed for each electron region –
whether it is a single, double, or triple bond.
2 electron regions: sp
3 electron regions: sp
2
4 electron regions: sp
3
5 electron regions: sp
3
d
6 electron regions: sp
3
d
2
VSEPR Summary – 2, 3, 4 e
regions
