Atomic Structure

Question 1

What are the stages of time of flight?

Answer 1

Ionisation, acceleration, ion drift, ion detection, data analysis

Question 2

How can mass spectrometry be used?

Answer 2

Environmental analysis, pharmaceutical analysis, forensic analysis

Question 3

What conditions does time of flight need?

Answer 3

A vacuum so there’s not interference from particles in the air

Question 4

What are the two methods of ionisation?

Answer 4

Electrospray and electron impact

Question 5

What is electrospray ionisation?

Answer 5

Sample dissolved in a volatile polar substance. Injected through needle at high voltage. Each particle gains a proton.

Question 6

What is electron impact?

Answer 6

High energy electrons are fired from an electron gun and knock off an electron from each particle.

Question 7

What happens in the acceleration stage?

Answer 7

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

Question 8

What determines the speed an ion travels?

Answer 8

Mass. Lower mass = faster, higher mass = slower

Question 9

What is the equation for kinetic energy?

Answer 9

KE = 1/2 mv^2

Question 10

What happens in the ion detection stage?

Answer 10

Positive ions hit the detector and pick up an electron which causes a current to flow showing the abundance.

Question 11

How are peaks displayed in data analysis?

Answer 11

Mass/charge (charge is normally one so it’s just mass)

Question 12

How do you calculate the mass in Kg of each particle?

Answer 12

m = mass number / (Avogadro’s constant)

1000

Question 13

What is the equation to calculate the mass or time if no KE is given?

Answer 13

m(1) / m(2) = t(1)^2 / t(2)^2

Question 14

What is the definition of relative atomic mass?

Answer 14

The average mass of one atom compared to one twelfth of the mass of one atom of carbon-12.

Question 15

What is the equation to calculate RAM from mass spectra?

Answer 15

Total (m/z of peak X abundance of that peak) / Total abundances

Question 16

What shows the Mr in a mass spectra of molecules?

Answer 16

Molecular ion peak (peak closest to right)

Question 17

What do you need to do when working out the Mr from a mass spectra?

Answer 17

Minus 1 because of the proton added during ionisation.

Question 18

What is the ratio of bromine isotopes?

Answer 18

79Br : 81Br 1:1

Question 19

What is the ratio of chlorine isotopes?

Answer 19

35Cl : 37Cl 3:1

Question 20

What is the electron shell order?

Answer 20

1s2s2p3s3p4s3d4p s=2 p=6 d=10

Question 21

What is the rule for adding and removing electrons between 4s and 3d?

Answer 21

4s fills first and is removed first

Question 22

What is the ionisation energy of an atom?

Answer 22

The minimum amount of energy needed to remove an electron from a gaseous atom.

Question 23

What is the trend in ionisation energy down a group?

Answer 23

Decreases because there’s more shielding, further from the nucleus

Question 24

What is the trend in ionisation energy across a period?

Answer 24

Increases because number of protons increases

Question 25

Where are the two deviations in ionisation energy?

Answer 25

Group 2 -> 3 and group 5 -> 6

Question 26

What happens between group 2 and 3?

Answer 26

The IE decreases because the electron is removed from a higher energy p sub level, less energy is needed.

Question 27

What happens between groups 5 and 6?

Answer 27

IE decreases because there’s a pair of electrons in a p orbital so there’s extra repulsion.