L5 - Electronic Configuration of the Atom (1)

Question 1

What observations does the quantum theory explain that classic mechanics cannot?

Answer 1

• Spectra of light emitted by atoms; quantisation of energy and energy levels
• Electrons in an atom are stable and stay in their orbitals
• Wave-particle duality: light can behave as if made up of photons with energy depending on frequency

Question 2

State the Uncertainty Principle.

Answer 2

“Can never know both the exact location and velocity of a subatomic particle at the same time.”

Question 3

Electrons can be described as _____ by the ___________ ________.

Answer 3

Electrons can be described as waves by the Schrodinger equation.

(A mathematical function that describes an electron’s properties in terms of quantum numbers).

Question 4

Describe a Hydrogen Spectrum.

Answer 4

• Electrons in an atom are in stable energy levels
• Absorption of a photon of light allows an electron to jump up to a higher level
• Moving down to a lower energy level emits a photon of light
• Measuring the energy of a photon allows the energy difference between levels to be determined; shows that energy levels are not equally spaced

Question 5

Define Ionisation Energy.

Answer 5

A measure of the amount of energy needed to remove electrons from atoms (or ions).

Question 6

Define First Ionisation Energy.

Answer 6

The energy required to remove one mole of electrons (to infinity) from one mole of gaseous atoms to form one mole of gaseous positive ions.

Question 7

Explain why ionisation energies are positive.

Answer 7

• As electrons are negatively charged and protons in the nucleus are positively charged, there will be an attraction between them
• Energy must be added to the system to pull the electron away

Question 8

Explain the relationship between nuclear charge and ionisation energy.

Answer 8

• The greater the pull of the nucleus, the harder it will be to pull an electron away from the atom
• Hence, the higher the nuclear charge, the higher the ionisation energy

Question 9

Define Electron Affinity.

Answer 9

The amount of energy needed to add electrons to atoms / ions.

Question 10

Define First Electron Affinity.

Answer 10

The energy required to add one mole of electrons to one mole of gaseous atoms to form one mole of gaseous negative ions.

Question 11

Why are First Electron Affinities negative?

Answer 11

First Electron Affinities are negative, indicating energy is released on addition of the electron.

Question 12

Describe the relationship between Electron Affinity and the ions formed.

Answer 12

The more negative the electron affinity, the more stable the negative ion that is formed.

Question 13

Explain trends (Atomic Size, First Ionisation Energy, First Electron Affinity) in the periodic table.

Answer 13

• Atomic Size: Increases down, and towards the left
• First Ionisation Energy: Increases up, and towards the right
• First Electron Affinity: Becomes more negative up, and towards the right

Question 14

Describe Quantum Numbers and explain what information they provide.

Answer 14

• Identify the various energy levels available within the atom in which the electron can reside

Identification numbers: ‘address’ for each electron in an atom:

1) Specify the position (or location) of an electron in an atom
2) Predict the direction of spin / rotation of the electron
3) Determine the energy and angular momentum of the electron

Question 15

4 Quantum Numbers are required to specify the character of an electron. State these.

Answer 15

• Principal Quantum Numbers (n)
• Azimuthal or Subsidiary Quantum Numbers (l)
• Magnetic Quantum Numbers (m)
• Spin Quantum Numbers (s)

Question 16

What is an orbital?

Answer 16

A region in space where there is a given (usually 95%) probability of finding a particular electron.

(Cannot specify the definite / exact position of an electron in an atom).

Question 17

In poly-electron atoms, principal energy levels are called ______.

Answer 17

Shells

Question 18

What letters are principal energy levels referred to by?

Answer 18

K, L, M, N

Question 19

n = ?

Answer 19

A number greater than 0.

Question 20

A group of orbitals with the same energy (equivalent) is called a ________.

Answer 20

Subshell

Question 21

l = ?

Answer 21

A value from 0 to (n-1).

Question 22

What letters are designated to the different sub-shells?

Answer 22

s, p, d, f

Question 23

What do the Principal Quantum Numbers (n) indicate?

Answer 23

• Distance of electron from the nucleus: The higher n, the further away the electron is from the nucleus
• Energy of electron: The higher n, the higher energy the electrons = less tightly held so they are easier to remove
• Number of electrons a shell can hold: n can have 2n^2 electrons

Question 24

What do the Azimuthal Quantum Numbers (l) indicate?

Answer 24

The sub-shell an electronic in:

• s: sharp
• p: principal
• d: diffuse
• f: fundamental

Question 25

Higher l, results in ______ ______.

Answer 25

Higher energy

Question 26

What is the maximum number of electrons a sub-shell can hold?

Answer 26

Max Electrons = 2(2l+1)

Question 27

What do the Magnetic Quantum Numbers (m/ml) represent?

Answer 27

• Represents the orbitals in a given sub-shell

- Indicates the direction of a particular orbital relative to the magnetic field / axes

Question 28

Magnetic Quantum Numbers do not indicate ______.

Answer 28

Energy

Question 29

‘m’ can have an integral value ranging from __________________.

Answer 29

‘m’ can have an integral value ranging from -l through 0 to +l

Question 30

For a given value of l, total number of m value is?

Answer 30

total number of m = (2l + 1)

Question 31

What different orbitals exist?

Answer 31

• 1 s orbital
• 3 p orbitals (px, py, pz)
• 5 d orbitals
• 7 f orbitals

Question 32

What do the Spin Quantum Numbers (s/ms) show?

Answer 32

An electron moving around the nucleus rotates or spins about its own axis (self-rotation) either in a clockwise or anti-clockwise direction.

These directions are described by the spin quantum number.

Question 33

What values can the Spin Quantum Numbers take?

Answer 33

• Clockwise spinning of electron = + 1/2

- Anticlockwise spinning of electron = - 1/2

Question 34

Two electrons in the same orbital must have ________ _____.

Answer 34

Opposite spins (Also known as anti-parallel spins)

Question 35

What does clockwise and anti-clockwise spinning of electrons produce?

Answer 35

Opposite magnetic fields

Question 36

State the restrictions of Principal, Azimuthal, Magnetic and Spin Quantum Numbers.

Answer 36

• Principal: Positive integer
• Azimuthal: Zero and positive integers less than n
• Magnetic: Integers between -l and +l
• Spin: + 1/2 or - 1/2