Exam Qs: Atomic Structure

Question 1

Explain why the 2nd ionisation energy is higher than the 1st ionisation energy.

Answer 1

• electron is being removed from a positive ion
• electron being removed is closer to the nucleus
• therefore needs more energy

Question 2

Define relative atomic mass.

Answer 2

the average mass of an atom compared to 1/12 the mass of a carbon-12 atom

Question 3

State how the relative molecular mass of a covalent compound is obtained from its mass spectrum.

Answer 3

Mr = highest m/z value

Question 4

State how to find the mass of a single atom.

Answer 4

relative atomic mass / avogadro’s constant

Question 5

Give two reasons why samples in mass spectrometry must be ionised.

Answer 5

• so that they can accelerate (towards the -ive plate)
• to deflect the beam

Question 6

Which ions in a mass spectrometer will be deflected the most?

Answer 6

• ones with the lowest m/z value (mass)

- as they are the lightest

Question 7

Explain how the relative abundance of an ion is measured in a mass spectrometer.

Answer 7

→ + ions reach detector
→ electrons are transferred from plate to + ions
→ this creates a flow of electrons
→ generates electric current
→ size of current is proportional to abundance

Question 8

State how to determine the Mr on a mass spectrum.

Answer 8

largest m/z value = Mr

Question 9

Explain how to find the molecular formula for a molecule.

Answer 9

• divide the Mr by the empirical formula mass

- multiply each subscript by the answer

Question 10

Name the 4 main steps in (TOF) mass spectrometry.

Answer 10

→ ionisation
→ acceleration
→ deflection
→ detection

Question 11

Explain how & why ions are accelerated in mass spectrometry.

Answer 11

• accelerated using an electric field
• so that all the ions have the same kinetic energy
• heavier atoms will travel slower

Question 12

Explain how & which ions are deflected in mass spectrometry.

Answer 12

• deflected using an electric field (electromagnet)

- lightest ions will be deflected the most (lowest m/z)

Question 13

State the two types of ionisation.

Answer 13

→ electron impact ionisation
→ electrospray ionisation

Question 14

Explain how electron impact ionisation works.

Answer 14

→ high energy electrons fired from electron gun

→ knocks off one electron

Question 15

Explain how electrospray ionisation works.

Answer 15

1. sample dissolved in volatile solvent
2. injected through fine needle to give a fine mist
3. needle tip is connected to + terminal of a high voltage power supply
4. particles are ionised by gaining a proton (an H+ ion) from solvent
5. as ions leave needle, the solvent evaporates

Question 16

What is the electronic configuration of copper?

Answer 16

1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d¹⁰

Question 17

What is the electronic configuration of chromium?

Answer 17

1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d⁵