Chem Bonding II

Question 1

How does hybridisation work

Answer 1

Equivalent hybrid orbitals are generated by mixing 1 2s orbital with [three/ two/ one] 2p orbitals, resulting in formation of [four sp3/ three sp2/ two sp] hybrid orbitals

Each of the hybrid orbitals overlaps with the __ orbital of the __ atom while unhybridised 2p orbitals on the atoms contain an unpaired electron, the side-on overlap of these unhybridised 2p orbitals give the pi bond

Unhybridised p orbitals are perpendicular to each other and the plan containing the sp orbital

sp_ hybridisation results in ___pair geometry

Question 2

Effect of hybridisation on bond length and bond strength

Answer 2

S orbital is spherical and electrons are closer to nucleus

Orbitals containing less p contain a higher s character

Higher s-character means
- hybrid orbital is less diffuse
- more effective overlap with orbital of other atom
- stronger bond and shorter bond length

Question 3

Resonance

Answer 3

Exhibits resonance when there is continuous side-on overlap of p-orbitals over at least 3 adjacent atoms, allowing for delocalisation of the pi electrons

Question 4

Conditions of resonance structures

Answer 4

Differ in placement of pi bonds and non-bonding electrons, while placement of atoms and sigma bonds stay the same

Question 5

Diamond bonding, why it has higher melting point than silicon

Answer 5

Each carbon atom is sp3 hybridised and covalently bonded to 4 other carbon atoms arranged tetrahedrally around it
Structure is extremely strong and rigid, diamond is an electrical insultaor
Due to strong covalent bonds, diamond has very high melting point and does not dissolve in any solvents

Valence orbitals of carbon is smaller and less diffuse than Si, there is more effective overlap between the carbon orbitals, resulting in C-C bond being stronger than Si-Si bond

Question 6

Bonding in graphite

Answer 6

• Layer structure, made up of planes of interconnected hexagonal rings of carbon atoms
• Each carbon atom is sp2 hybridised and forms three sigma bonds with 3 other carbon atoms
• Each carbon has unhybridised p-orbital which contains single electron
  ->P-orbital overlaps continuously with p-orbitals of its immediate neighbours, resulting in pi electron cloud above and below the plane containing carbon atoms
  -> pi electrons delocalised over whole layer so graphite is an electrical conductor
  -> Graphite can only conduct electricity in direction parallel to layers

Attraction between carbon atoms within each layer is due to strong covalent bonding, but attraction between different layers due to weak id-id forces
-> Lot of energy is required to overcome strong covalent bonds within each layer

Question 7

Why graphite has higher melting point than diamond

Answer 7

Each carbon atom in graphite has unhybridised p orbital containing one electron each
- P orbital of one carbon atom overlaps collaterally with the p orbitals of immediate neighbour
- Additional electron density between carbon atoms holding nuclei more closely, strengthening C-C bond

Hybrid orbitals of carbon atoms in graphite has higher s character than diamond, less diffuse and overlap of sp2 hybrid orbitals in graphite is more effective than overlap of sp3 hybrid orbitals in diamond