6. Lewis and Valence Bond thoeries of bonding

Question 1

What are diatomic and polyatomic molecules?

Answer 1

Diatomic - 2 atoms combined

Polyatomic - many atoms

Question 2

What are the types of bonding depending on the level of e sharing?

Answer 2

Question 3

What is the potential E well?

Answer 3

Highest potential E when a bond is formed → stable

Without the well → no stable bond - molecule not possible

The larger the well → the more stable the bond

Question 4

What are the models of bonding?

Answer 4

Question 5

Explain Lewis bonding model

Answer 5

• favours octet - noble gas configuration
• pairs of e not used in bonds are called lone pairs
• quite simple model, doesn’t explain paramagnetism (O₂ paramagnetic although all e- are paired)

Question 6

What is paramagnetic?

Answer 6

Paramagnetic molecules - those which have unpaired e

Question 7

What is the use of Schrodinger in figuring out bond in molecules (multielectron systems)?

Answer 7

• Schrodinger equation can’t be solved for molecules (multielectron systems) but approximations can be made: lead to valance bond theory / molecular orbital theory - both use the fact that orbitals can be combined (mixed)

Question 8

How can d orbitals be combined?

Answer 8

Solving the Schrodinger equation → the only possible nr of d orbitals is 5 → doesn’t fit with 6 regular orbitals (would interact if not combined) → need to combine two orbitals to get 5 instead 6:

add positivephase orbitals together in z direction → make up rings - two orbitals combined into one new orbital

Question 9

How can p orbitals be combined?

Answer 9

Question 10

Explain valence bond theory for H₂ (equations)

Answer 10

• orbitals (wavefunctions) can be combined on the same atom to form hybrid orbitals (at the start while in molecular orbital theory - at the end are hybridised)
• orbitals (wavefunctions) can be combined to form bonds (in phase / out of phase)
• bonds can be the average of different resonance forms
• VB - the 3D drawing theory

Question 11

Explain valence bond theory for N₂ (image wise)

Answer 11

1. Negative phase s orbital combined with negative phase p orbital - constructive interference (phases are the same which mix)
2. Positive s orbital combined with negative p orbital - destructive interference (phases which mix are different)

Question 12

How do sp and p orbitals combine to form bonds?

Answer 12

sp - by the ends

p - by the sides

Question 13

What happens when two orbitals get closer?

Answer 13

Orbitals are influenced by each other → deform

If close enough → form bonds