Lecture 1: intro and basics of molecular structure Flashcards
What is an orbital?
A region where there is a calculated 90% probability of finding an electron
What are degenerate orbitals?
Orbitals that have the same amount of energy
What are the names of the rules that govern the placement of electrons into orbitals?
- Aufbau Principle
- Pauli exclusion principle
- Hund’s rule
What is the Aufbau principle?
It states that the lowest energy orbital has to be filled first
What is the Pauli exclusion principle?
It states that only 2 electrons can occupy the orbital, and they must have opposite spin.
What is Hund’s rule?
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
_______ interference between 2 atomic orbitals will result in a bond
Constructive
The greater the amount of orbital overlap, the ______ the bond
Stronger
What does the valence bond theory state?
A bond is formed when atomic orbitals overlap
- constructive and destructive intereference
What does the molecular orbital theory state?
- Atomic orbitals are mathematically combined to produce new orbitals called molecular orbitals
- When 2 atomic orbitals overlap, they cease to exist, and are replaced by molecular orbitals
The number of atomic orbitals is __________ the number of molecular orbitals
equal to
Do the three rules governing the placement of electrons in atomic orbitals hold for molecular orbitals?
yes
How to calculate bond order?
bond order = (number of electrons in bonding MO - number of electrons in antibonding MO) / 2
What does bond order tell us?
The number of bonds between 2 atoms
Why do sp hybridized orbitals have lower energy than unhybridised p orbitals?
Because the hybridized orbitals are a mix of the s and p orbitals, and s orbitals have lower energy than p orbitals
Is a sigma bond stronger or a pi bond?
- Sigma bond
- Because there is greater and more efficient overlap between the hybridised orbitals
Which bond is loner, an sp3-sp3 bond or an sp-sp bond?
- sp3-sp3
- It has greater p character, which has a dumbbell shape and is longer
How to calculate steric number?
steric number = number of sigma bonds + number of lone pairs
How to predict the hybridisation of the central atom using steric number?
Steric number 4 : sp3
Steric number 3 : sp2
Steric number 2 : sp
What is the difference between molecular geometry and electron group geometry?
- 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
- essentially molecular geometry just ignores the lone pairs
How do you calculate dipole moment?
dipole moment (μ) = charge (in esu) x the distance the 2 opposite charges are separated (in cm)
How to convert esu to debye?
1 debye (D) = 10^-18 esu
If the bond between 2 atoms is ionic, what would the full charge separation be?
4.80 x 10^-10 esu
