3.1.1.2 Mass number and Isotopes

Question 1

What is the Mass Number and its symbol?

Answer 1

Mass Number
* This is the total number of protons and neutrons in the nucleus of an atom
* It is represent by A

Question 2

What is the Atomic (proton) Number and its symbol?

Answer 2

Atomic (proton) Number
* This is the total number of protons in an atom
* All atoms of this element have the same number of protons

Question 3

What are isotopes?

Answer 3

Isotopes are atoms that have the same number of protons but different number of neutrons in the nucleus.

Question 4

What does a ToF Mass Spectrometer measure?

Answer 4

A ToF mass spectrometer gves information about the relative atomic mass of the elements and its abundance of its isotopes.

Question 5

What are the main stages of ToF?

Answer 5

1. Ionisation (Electrospray ionisation/Electron impact ionisation)
2. Acceleration
3. Ion Drift
4. Detection

Question 6

What is Ionisation in ToF and its types?

Answer 6

The process where the sample is ionised
Electrospray Ionisation
Electron impact ionisation

Question 7

What is the process of Electrospray Ionisation?

Answer 7

1. High Mr substance
   2.Dissolve it in VOLATILE solvent and force it into a thin HYPODERMIC needle
2. The needle is then connected to a positive voltage
3. Due to the voltage, they gain a H+ ion making them all positively charged
4. Solvent is then removed, which leaves a gas made of positive ions
5. Acceleration, Ion drift, Detection

Question 8

What is the process of Electron Impact ToF?

Answer 8

1. Low Mr substance
2. Sample is vaporised and an ‘electron gun’ fires high energy electrons at it.
3. This knock one electron off each particle making them positively charged (X+ ions)
4. Acceleration, Ion drift and detection

Question 9

What is acceleration in ToF?

Answer 9

1. The positive ions accelerate in an electrical field
2. This field gives every all the ions the same amount of kinetic energy
3. Therefore the lighter particles will travel faster while the heavier particles will travel slower due to KE = 1/2mv^2

Question 10

What is the Ion Drift stage in ToF?

Answer 10

Ions enter a field where no electric current is present so they travel at the same speed as in the acceleration stage

Question 11

What is the Detection stage in ToF?

Answer 11

1. Lighter ions travel faster so they get detected first
2. Therefore detector detects the current that is produced when the ion hits the detector