Shapes of Molecules

Question 1

State the shape and bond angles for each molecules:

a) NH4+
b) H2O
c) BeCl2
d) SF6
e) NH3
f) SO2

Answer 1

a) Tetrahedral - 109.5 degrees
b) Bent (V-shaped) - 104.5 degrees
c) Linear - 180 degrees
d) Octahedral - 90 & 180 degrees
e) Pyramidal - 107 degrees
f) Bent - 119 degrees (Sulfur has 1 lone & 2 bonding pairs)

Question 2

State the shape and bond angles for each of these organic molecules:

a) Alkenes
b) Alkanes
c) Alcohols
d) Carboxylix acids
e) Halogenoalkanes
f) Aldehydes & ketones

Answer 2

a) 118 degrees (HCH), 121 degrees (CCH)
b) Tetrahedral - 109.5 degrees
c) Bent - 104 degrees (COH), tetrahedral - 109.5 degrees (HCH)
d) Planar - 120 degrees (OCO), bent - 104 degrees (COH)
e) Tetrahedral - 109.5 degrees
f) Planar - 120 degrees

Question 3

Describe the structure and properties of Diamond.

Answer 3

Giant covalent structure
Chemically inert
Colourless and transparent 
Electrical insulator (poor conductor)
Hardest substance known

Question 4

Compare and contrast the structures of Graphite and Fullerenes.

Answer 4

Graphite: planes of trigonal carbon atoms, 3D crystals; conductor; inert
strong covalent bonds within layers
Weak London forces between layers - 1 electron per carbon is delocalised, so greater electrical conductivity in the plane (electrons can move). Energy gap is too large perpendicular to plane.

Fullerenes: spherical MOLECULAR structure of 60 carbons; black solid; conducts electricity (delocalised electrons)

Question 5

State three possible uses of nanotubes (probes and particles).

Answer 5

1. To deliver drugs to cells
2. To circulate in the blood and identify cancerous cells
3. To be used in cosmetics and sunscreen

Question 6

Define:

a) bond length

b) bond angle

Answer 6

a) the distance between nuclei and two bonded atoms in a molecule
b) the angle made between two adjacent bonds in the space around the central atom in a molecule