atomic structure

Question 1

What are the three subatomic particles in an atom?

Answer 1

Proton, neutrons and electrons

Question 2

What are the relative masses and charges of the subatomic particles?

Answer 2

Proton: mass = 1, charge = +1 | Neutron: mass = 1, charge = 0 | Electron: mass ≈ 0, charge = –1

Question 3

What is the atomic number (Z)?

Answer 3

The number of protons in the nucleus of an atom.

Question 4

What is the mass number (A)?

Answer 4

The total number of protons and neutrons in the nucleus.

Question 5

What are isotopes?

Answer 5

Atoms of the same element with the same number of protons but different numbers of neutrons.

Question 6

Why do isotopes of the same element react chemically the same?

Answer 6

Because they have the same electron configuration.

Question 7

What is mass spectrometry used for?

Answer 7

To determine the relative atomic mass

Question 8

What are the four key stages of time-of-flight (TOF) mass spectrometry?

Answer 8

1. Ionisation | 2. Acceleration | 3. Ion drift | 4. Detection

Question 9

What are the two main ionisation methods in TOF mass spectrometry?

Answer 9

Electrospray ionisation and electron impact ionisation.

Question 10

What happens in electrospray ionisation?

Answer 10

Sample is dissolved in a volatile solvent and injected through a fine needle with high voltage

Question 11

what ion is typically formed in electrospray ionisation?

Answer 11

XH+

Question 12

Why is electrospray ionisation suitable for large organic molecules?

Answer 12

It causes little fragmentation.

Question 13

What happens in electron impact ionisation?

Answer 13

High-energy electrons are fired at the sample

Question 14

What ion is produced in electron impact ionisation?

Answer 14

A molecular ion (M⁺).

Question 15

Why is electron impact ionisation not used for large molecules?

Answer 15

It causes significant fragmentation.

Question 16

What happens during the acceleration stage of TOF mass spectrometry?

Answer 16

Positive ions are accelerated by an electric field to a constant kinetic energy.

Question 17

Why do lighter ions reach the detector faster?

Answer 17

They have higher velocities due to their smaller mass.

Question 18

What happens during ion drift?

Answer 18

Ions travel through a region with no electric field; lighter ions drift faster.

Question 19

What happens at the detector in a TOF mass spectrometer?

Answer 19

Ions hit the detector

Question 20

What is the size of the current at the detector proportional to?

Answer 20

The abundance of the ions hitting the detector.

Question 21

How is relative atomic mass calculated from a mass spectrum?

Answer 21

Relative atomic mass = ∑(isotope mass × abundance) / ∑(abundance)

Question 22

Equation for kinetic energy in TOF mass spectrometry?

Answer 22

KE = ½ mv²

Question 23

Equation for velocity of an ion?

Answer 23

d = t × v (where d = length of drift tube

Question 24

What are the 4 stages of TOF mass spectrometry?

Answer 24

Ionisation → Acceleration → Ion drift → Detection

Question 25

What happens during electron impact ionisation?

Answer 25

Electrons knock out an electron from the sample

Question 26

What happens during electrospray ionisation?

Answer 26

Sample is dissolved

Question 27

What happens during the acceleration stage in TOF MS?

Answer 27

Ions are accelerated to the same kinetic energy by an electric field.

Question 28

What happens during ion drift?

Answer 28

Ions enter a field-free region; lighter ions drift faster.

Question 29

What happens at the detector in TOF MS?

Answer 29

Ions hit the detector

Question 30

Equation for kinetic energy?

Answer 30

KE = ½ mv²

Question 31

Equation for velocity?

Answer 31

d = t × v

Question 32

What is the relationship between time of flight and ion mass?

Answer 32

Time is proportional to √mass

Question 33

What is the order of electron sublevels up to 4p?

Answer 33

1s

Question 34

What are the two exceptions in electronic configurations?

Answer 34

Chromium (Cr) = [Ar] 4s¹ 3d⁵ | Copper (Cu) = [Ar] 4s¹ 3d¹⁰

Question 35

How are electrons arranged in orbitals according to the Aufbau principle?

Answer 35

Electrons fill the lowest available energy level first.

Question 36

What is Hund’s rule?

Answer 36

Electrons fill orbitals singly with parallel spins before pairing up.

Question 37

What is Pauli’s exclusion principle?

Answer 37

An orbital can hold a maximum of two electrons with opposite spins.

Question 38

What is first ionisation energy?

Answer 38

The energy required to remove one mole of electrons from one mole of gaseous atoms.

Question 39

What are the factors affecting ionisation energy?

Answer 39

Nuclear charge (↑ = ↑IE) | Atomic radius (↑ = ↓IE) | Electron shielding (↑ = ↓IE)

Question 40

What is the general trend in ionisation energy across a period?

Answer 40

Increases → nuclear charge increases

Question 41

Why does ionisation energy decrease down a group?

Answer 41

More shells → more shielding → greater atomic radius → weaker nuclear attraction.

Question 42

Why is there a drop in ionisation energy between Group 2 and Group 3?

Answer 42

Electron enters a higher energy p-orbital → more shielding

Question 43

Why is there a drop between Group 5 and Group 6?

Answer 43

Electron pairing in the same p-orbital → increased repulsion → easier to remove.

Question 44

Convert kilojoules to joules

Answer 44

1 kJ = 1000 J

Question 45

Convert milliseconds to seconds

Answer 45

1 ms = 0.001 s

Question 46

Convert nanoseconds to seconds

Answer 46

1 ns = 1 × 10⁻⁹ s

Question 47

Convert grams to kilograms

Answer 47

1 g = 0.001 kg

Question 48

What is the unit of mass in TOF equations?

Answer 48

Kilograms (kg)

Question 49

What is the unit of time in TOF equations?

Answer 49

Seconds (s)

Question 50

What is the unit of kinetic energy in TOF?

Answer 50

Joules (J)

Question 51

explain how ions are detected and relative abundance is measured in a TOF mass spectrometer (2)

Answer 51

- ion hits detector AND gains an electron (creating a current) - abundance is proportion (to size of) current