14.2.1 Describe sigma and pi bonds
- sigma bonds are single bonds and is the first bond in a double/triple bond. They result from an axial overlap of orbitals, either an s orbital with another s orbital, a s with a p, or a p with a p
- pi bonds are the subsequent second and third bonds in a double/triple bond (but they never exist without a sigma bond). They result from a sideways overlap of parallel p orbitals
- double bonds are formed from one sigma and one pi bond
- triple bonds are formed from one sigma and two pi bonds
14.2.2 Explain hydridization in terms of the mixing of atomic orbitals to form new orbitals for bonding
sp3 Hybridization:
sp2 Hybridization:
sp Hybridization:
- to facilitate bond formation, atoms can recombine orbitals in their outer shell (main energy level)
- hydridization is the mixing of original orbitals on an isolated atom to form special atomic orbitals for bonding
- using VSEPR, figure out how many charge centers surround the central atom
- the required # of original orbitals in the central atom will hybridize
sp3 Hybridization:
- eg. methane (CH4)
- one of the two electrons in the 2s orbital is promoted to a higher energy level, one of the 2p orbitals so that the three 2p orbitals are all half-full
- the 2s and three 2p orbitals now all have 1 electron each and they hybridize to form bonding orbitals that are all lower in energy than the 2p orbitals, energetically more favourable
sp2 Hybridization:
- eg. ethene
- one of the 2s electrons are excited to 2p again
- the 2s and two 2p orbitals hybridize, one 2p orbital remains
- this remaining 2p orbital can overlap with another remaining orbital in another carbon atom to form a pi bond, resulting in a planar molecule with a region of electron density above and below the plane
sp Hybridization:
- eg. ethyne
- the 2s orbital and just one 2p orbital hybridizes
- the remaining two 2p orbitals on each carbon atom overlap to form two pi bonds
14.2.3 Identify and explain the relationships between Lewis structures, molecular shapes, and types of hydribization (sp, sp2, and sp3)
- molecular shapes can be arrived at by using either VSEPR or knowing the type of hybridization
- hybridization can take place between any s and p orbital in the same energy level and is not restricted to just carbon compounds
- if shape and bond angles known from Lewis structures, then type of hybridization can b deduced and vice versa