2.2. Molecular Orbitals Flashcards
Order molecular and atomic orbitals in increasing energy.
Bonding molecular orbital -> atomic orbital -> antibonding molecular orbital.
What happens when atomic orbitals overlap end-on along an axis?
A sigma bond is formed.
If two p orbitals overland end-on perpendicular to an axis what happens?
A pi bond is formed.
What bonds are present in a double bond?
One sigma and one pi bond.
What bonds are present in a triple bond?
One sigma and two pi bonds.
Which are weaker, pi or sigma bonds?
Pi bonds as the side-on overlap is much less efficient.
What is hybridisation?
The process of mixing atomic orbitals in an atom to create new orbitals called hybrid orbitals.
What type of hybridisation does carbon have in alkanes?
sp3 hybridisation.
What type of molecular bonding happens in alkanes, and what orbitals overlap?
1s orbitals of hydrogen overlap with the sp3 orbitals of the carbon creating sigma bonds.
What type of molecular bonding happens in alkenes, and what orbitals overlap?
sp2 hybridisation happens between the 2s and two 2p orbitals to create three sp2 orbitals. These sp2 orbitals overlap with the 1s orbitals of the hydrogens to form sigma bonds. On each carbon there is still an unhybridised p orbital which overlaps side on with another unhybridised p orbital creating pi bonds.
Only the carbons involved in the double bond are sp2 hybridised.
What do orbitals look like in non-polar covalent molecules?
They are symmetrical at the midpoint of the two atoms.
What do orbitals look like in polar covalent molecules?
They have a larger part on the side of the atom with a slightly negative charge.
What do orbitals look like in ionic molecules?
The orbitals only embrace the negative ion in the bond.
What type of bonding happens in alkynes?
sp hybridisation occurs here when one 2s orbital and one 2p orbital hybridise. The remaining orbitals are left unhybridised. These two unhybridised p orbitals overlap side on with other unhybridised p orbitals and form pi bonds.
Why are most organic compounds colourless?
They absorb wavelengths that aren’t in the visible spectrum.
