Secondary Bonding. On Saturn’s moon Titan, typical surface temperatures range ar

Question

Secondary Bonding.

On Saturn’s moon Titan, typical surface temperatures range around 94 K.
Thus, Titan has been found to feature oceans made of liquid methane (CH4, melting point: 91 K,
boiling point: 111.5 K). In contrast to earth, rocks on Titan consist of H2O.
(a) What type of secondary bond do you expect to dominate between individual molecules in
solid and liquid methane? Why? How does this explain the low melting point of CH4?
(b) How is this different from the type of secondary bonding that you would expect in liquid or
solid water? Explain your answer. How does this explain the existence of liquid water (rather
than just water vapor) on Earth?
(c) For solid or liquid NH3 (between H2O and CH4), based on the elements’ electronegativities,
which type of secondary bonding do you expect to dominate?

Explanation / Answer

a)
Methane is an non polar molcule.
Secondary bonds between them will be Vander walls force of attraction or london forces.
Since these interactions are very weak, they have very low melting point

b)
Water is very polar molecule in which Hydrogen is attached to Oxygen, an electronegative element. So secondary bonding here is hydrogen bonding. These bonding are very strong and hence water has high boiling point. SO water will rather exist in liquid form.

c)
In NH3 also there will be hydrogen bonding because N is electronegative but this Hydrogen bonding will be weaker than in water. They will stronger than bonding in CH4

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