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Question 1

When do molecular orbitals resemble the parent atoms?

Answer 1

If two combining orbitals do not have the same energy, the greater the difference the more closely the resulting molecular orbital resembles the parents.

Question 2

Trend of atomic orbital energies in period table.

Answer 2

Atomic orbital energies decrease across a period as effective nuclear charge increases, since e-s are more attracted to the nucleus. Energy gap between s & p increases.

Question 3

Describe MO of HF.

Answer 3

The two F 2p orbitals (called 1pe in molecule) are non bonding (house lone pairs). 2sigma combination orbital is somewhat bonding but mainly F 2p in character. 1sigma combination orbital is almost entirely F character. the F 2s & H 1s orbitals are so different in energies that they barely interact, which means another lone pair on F.