2) (40 pts) In two or three sentences, briefly answer the following conceptual questions. a) (10 pts) With valence bond theory, briefly explain why burger is a good representation for a double bond. You can use ethylene (H2C=CH2 ) as an example. b) (10 pts) Why there does not exist a 3f atomic orbital? c) (10 pts) What are the advantages and disadvantages of the valence bond theory to describe a polar covalent bond? You can use HF as an example. d) (10 pts) With LCAO-MO theory, briefly explain why Nez is not a stable molecule