Lecture 1: intro and basics of molecular structure

Question 1

What is an orbital?

Answer 1

A region where there is a calculated 90% probability of finding an electron

Question 2

What are degenerate orbitals?

Answer 2

Orbitals that have the same amount of energy

Question 3

What are the names of the rules that govern the placement of electrons into orbitals?

Answer 3

1. Aufbau Principle
2. Pauli exclusion principle
3. Hund’s rule

Question 4

What is the Aufbau principle?

Answer 4

It states that the lowest energy orbital has to be filled first

Question 5

What is the Pauli exclusion principle?

Answer 5

It states that only 2 electrons can occupy the orbital, and they must have opposite spin.

Question 6

What is Hund’s rule?

Answer 6

It states that if 2 or more empty orbitals of equal energy are available, then the electrons will individually occupy the orbitals with their spins parallel until all are half filled

Question 7

_______ interference between 2 atomic orbitals will result in a bond

Answer 7

Constructive

Question 8

The greater the amount of orbital overlap, the ______ the bond

Answer 8

Stronger

Question 9

What does the valence bond theory state?

Answer 9

A bond is formed when atomic orbitals overlap
- constructive and destructive intereference

Question 10

What does the molecular orbital theory state?

Answer 10

1. Atomic orbitals are mathematically combined to produce new orbitals called molecular orbitals
2. When 2 atomic orbitals overlap, they cease to exist, and are replaced by molecular orbitals

Question 11

The number of atomic orbitals is __________ the number of molecular orbitals

Answer 11

equal to

Question 12

Do the three rules governing the placement of electrons in atomic orbitals hold for molecular orbitals?

Answer 12

yes

Question 13

How to calculate bond order?

Answer 13

bond order = (number of electrons in bonding MO - number of electrons in antibonding MO) / 2

Question 14

What does bond order tell us?

Answer 14

The number of bonds between 2 atoms

Question 15

Why do sp hybridized orbitals have lower energy than unhybridised p orbitals?

Answer 15

Because the hybridized orbitals are a mix of the s and p orbitals, and s orbitals have lower energy than p orbitals

Question 16

Is a sigma bond stronger or a pi bond?

Answer 16

1. Sigma bond
2. Because there is greater and more efficient overlap between the hybridised orbitals

Question 17

Which bond is loner, an sp3-sp3 bond or an sp-sp bond?

Answer 17

1. sp3-sp3
2. It has greater p character, which has a dumbbell shape and is longer

Question 18

How to calculate steric number?

Answer 18

steric number = number of sigma bonds + number of lone pairs

Question 19

How to predict the hybridisation of the central atom using steric number?

Answer 19

Steric number 4 : sp3
Steric number 3 : sp2
Steric number 2 : sp

Question 20

What is the difference between molecular geometry and electron group geometry?

Answer 20

1. Molecular geometry is the arrangement of atoms around the central atom in a molecule, whereas the electron geometry is the arrangement of electron pairs around the central atom
2. essentially molecular geometry just ignores the lone pairs

Question 21

How do you calculate dipole moment?

Answer 21

dipole moment (μ) = charge (in esu) x the distance the 2 opposite charges are separated (in cm)

Question 22

How to convert esu to debye?

Answer 22

1 debye (D) = 10^-18 esu

Question 23

If the bond between 2 atoms is ionic, what would the full charge separation be?

Answer 23

4.80 x 10^-10 esu