Molecular Orbitals Flashcards
What can molecular orbital theory do?
Provide explanation for more complex molecules
Formation of molecular orbitals
When atomic orbitals combine
Determination of the number of molecular orbitals
Equal to the number of atomic orbitals that combine
What is formed in the combination of two atomic orbitals
A binding molecular orbital and an antibonding orbital
What does the binding molecular orbital encompass?
Both nuclei
Basis of bonding
Attraction of the positively charged nuclei and the negatively charged electrons in the binding molecular orbital
Maximum number of electrons held in each molecular orbital
Two
Non-polar covalent bond bonding orbital
Symmetrical about the midpoint
Polar covalent bond bonding molecular orbital
Asymmetrical about the midpoint
Atom with greater negativity has greater share of the bonding electrons
Ionic compounds bonding molecular orbitals
Most extreme case of asymmetry
Bonding molecular orbitals almost entirely located around one atom resulting in the formation of ions
Sigma bonds
Molecular orbitals formed from end-on overlap of atomic orbitals that lie along the axis of the covalent bond
Present in all bonds
Pi bonds
Molecular orbitals formed from side-on overlap of parallel atomic orbitals that lie perpendicular to the axis of the covalent bond
1 present in double bonds, 2 present in triple bonds
Hybridisation
Mixing atomic orbitals within an atom to generate a set of new atomic orbitals called hybrid orbitals which are degenerate
Explains the bonding and shape of molecules of carbon
Hybridisation in Alkanes
2s orbital and three 2p orbitals hybridise to form four degenerate sp3 hybrid orbitals
Tetrahedral arrangement
sp3 orbitals overlap end on with other atomic orbitals to form sigma bonds
Hybridisation in Alkenes
2s orbital and two 2p orbitals hybridise to form three degenerate sp2 hybrid orbitals
Trigonal planar arrangement
Hybrid sp2 orbitals overlap end on to form sigma bonds
What happens to the remaining 2p orbital in the hybridisation of Alkenes?
Remaining 2p orbital on each carbon atom of the double bond is unhybridised and lies perpendicular to the axis of the sigma bond
Unhybridised p orbitals overlap side on to form pi bonds
Bonding in benzene and other aromatic systems
Six carbon atoms in benzene are arranged in a cyclic structure with sigma bonds between the carbon atoms
What happens with the unhybridised p orbitals in benzene?
Overlap side on to form a pi molecular system perpendicular to the plane of the sigma bonds
Extends across all six carbon atoms
Electrons in the aromatic pi molecular system
Delocalised
Bonding in alkynes
2s orbital and one 2p orbital of carbon hybridise to form two degenerate hybrid orbitals
Linear arrangement
Hybrid sp orbitals overlap end on to form sigma bonds
What happens to the remaining p orbitals on each carbon in alkynes?
Lie perpendicular to each other and to the axis of the sigma bond
Unhybridised p orbitals overlap side on to form pi bonds
HOMO
Highest occupied molecular orbital
LUMO
Lowest unoccupied molecular orbital
Molecular orbital theory and colour of organic molecules
