1.1 Atomic Structure

Question 1

Relative charge and mass of a proton?

Answer 1

Charge: +1
Mass: 1

Question 2

Relative charge and mass of an electron?

Answer 2

Charge: -1
Mass: 1/1840

Question 3

Relative charge and mass of a neutron?

Answer 3

Charge: 0
Mass: 1

Question 4

If an element is described as an atom what is significant?

Answer 4

It has the same amount of electrons as the protons

Question 5

Why are there decimals numbers for some of the atomic mass numbers?

Answer 5

There are can be many isotopes of an element therefore an average is taken to acquire the number

Question 6

What are the properties of an isotope?

Answer 6

Same number of protons and electrons
Different number of neutrons
Identical chemical properties because of the same electron configuration

Question 7

How do you identify an element?

Answer 7

Using the atomic number/proton number

Question 8

What is mass spectrometry?

Answer 8

It can identify relative isotopic mass
The relative abundance of isotopes
It can be used to identify elements
It can be used to determine relative molecular mass

Question 9

What kind of mass spectrometer do we learn about?

Answer 9

Time of Flight

TOF

Question 10

What must be present within the mass spectrometer?

Answer 10

Kept under vacuum to reduce the possibility of intermolecular collisions
E.g between the sample and the air
This is because it would interfere with the accuracy of the process

Question 11

What are the stages of mass spectrometry?

Answer 11

Vaporisation
Ionisation 
Acceleration 
Ion Drift
Detection 
Data Analysis

Question 12

What happens in vaporisation?

Answer 12

The sample has to be turned into a gas if it isn’t already

Question 13

What does ionisation do to the sample in mass spectrometry?

Answer 13

Mass spectrometry can only work if the particles are charged and usually positive ions are generated
This is so you can control the particles much easier

Question 14

What are the types of Ionisation?

Answer 14

Electron Impact

Electrospray

Question 15

How does electron impact work?

Answer 15

It is the traditional method for producing ions in MS
It involves bombardment of the sample with a high energy beam of electrons
When the electrons hit the sample they sometimes remove another electron

The electrons fired are not absorbed

M + e- ——> M+ + 2e-

Question 16

What can happen with electron impact?

Answer 16

It can often result in fragmentation

Question 17

How does ionisation by Electrospray work?

Answer 17

Sample is dissolved in a volatile solvent
Forced into a fine hollow needle
This is connected to the positive terminal of a high voltage supply
The mixture is sprayed as a fine mist of droplets with the solvent evaporated
The sample picks up a proton (H+ ion) or sometimes ammonium salts are used

M + H+ ——> MH+

Question 18

Which of the two ionisation techniques are better for larger molecules? Why?

Answer 18

Electrospray

It is considered a ‘soft’ ionisation technique as it is less likely to fragment the sample

Question 19

What happens during acceleration?

Answer 19

The positive ions are attracted towards a negatively charged plate
The speed they reach is dependent on their mass to charge ratio
They are forced into a thin beam

Question 20

What happens in ion drift?

Answer 20

They ions are separated according to how fast they travel through a ‘drift chamber’
They have different velocities because of their different masses
The ions are accelerated with the same kinetic energy because of the electric field they are in
Atoms with a lower mass have a higher velocity so arrive at the detector before those with a higher mass

Question 21

What is the equation for kinetic energy?

Answer 21

KE = 1/2 mv^2

Question 22

What happens at detection?

Answer 22

Ions hit a negatively charged plate and a current is generated when an electron is accepted and the positive ion is discharged
The time of flight of the ion is recorded

Question 23

In detection what is the size of the current related to?

Answer 23

The number of ions hitting the detector

Question 24

What is acquired in data analysis?

Answer 24

The mass to charge ratio of the ions and their relative abundance

Question 25

How do you calculate RAM from mass spectrometry?

Answer 25

(Mass to charge ratio x relative abundance) + (repeat for as many)
Divided by total number of ions

Question 26

What is the highest peak on a mass spectrum in Electrospray ionisation? What do you have to remember?

Answer 26

Protonated molecular ion peak

You have to take one away as a hydrogen was absorbed in the ionisation

Question 27

What is the benefit of low resolution spectrometry?

Answer 27

It is cheaper

Question 28

What is the benefit of high resolution spectrometry?

Answer 28

You can see more detail and distinguish between substances with a similar RAM