Atomic strucuture

Question 1

What is the mass number?

Answer 1

The number of protons and neutrons

Question 2

What is the atomic number?

Answer 2

The number of electrons and protons

Question 3

How do isotopes differ to atoms?

Answer 3

They are of the same element but with a different mass number
they have the same chemical properties but different physical properties
- lower density
- faster rates of diffusion
- lower melting and boiling points

Question 4

What is relative isotopic abundance?

Answer 4

The percentage of each isotope in a sample that is present in nature

Question 5

What is the mass spectrometer ?

Answer 5

An instrument to accurately determine the relative isotopic mass and the relative abundance of isotopes
also separates atoms or molecules according to there charge and mass

Question 6

What are the 4 stages in a mass spectrometer?

Answer 6

Ionisation - where the atoms are converted into a +1 ion
Acceleration- where the ions move at the same speed
Flight tube - time taken for them to travel a fixed distance
Detection- when they arrive at a detector

Question 7

Describe the two ways ionisation occurs ?

Answer 7

Electron gun ionisation- the sample is gaseous and hit with high energy electrons from an electron gun which knocks off the outer shell electron
Electro spray ionisation - add a proton in the form of H+, once the sample has dissolved in a solvent of H+ ions
It is pushed through a needle with high voltage and the protons will stick

Question 8

Describe acceleration

Answer 8

The positively charged ions are attracted by the negatively charged plate. The ions of the same charge will move at the same speed so they will have the same kinetic energy

Question 9

Describe the flight tube

Answer 9

The ions will pass through into a tube the time of flight of each particle. The time taken depends on the velocity which depends on the mass of the ion

Question 10

Ion detector

Answer 10

The ion detector is a negatively charged
As the ion hits the detector they produce an electric current
A high current means a high abundance of the specific ion
The mass spectrometer converts the size of the current into a peak on a mass spectrum

Question 11

One of the methods of ionising samples for TOF mass spectrometry is by electron impact. How is this ionisation done?

Answer 11

High energy electrons are fired from an electron gun at the sample
which knocks off one electron

Question 12

A method of ionising samples is by electrospray ionisation. How is this done?

Answer 12

Dissolve sample in a volatile solvent
injected through a fine needle at high voltage
to gain a proton

Question 13

explain why different ions take different tmes to travel through the flight tube

Answer 13

Due to the velocity of the

Question 14

What is the difference between the rutherford model and the current atomic model?

Answer 14

The atomic model has protons and neutrons
The current model shown electrons in different energy levels/orbitals

Question 15

Define relative atomic mass

Answer 15

The average mass of an isotope of an element compared to 1/12th of the mass of carbon 12

Question 16

Explain why it is necessary to ionise molecules when measuring their mass in a TOF mass spectrometer

Answer 16

Ions not molecules will interact with and be accelerated by an electric field
Only ions will create a current when hitting the detector.

Question 17

state the role of water in the reaction with calcium

Answer 17

To be an oxidizing reagent

Question 18

State and explain the trend in the first ionization energies of the elements in the group 2 from magnesium and to barium

Answer 18

A decreasing trend
As Ions get bigger they have a weaker attraction to lost ion

Question 19

state the element in period 3 that has the highest first ionization energy

Answer 19

Argon- Largest proton so has largest nuclear charge but has the same amount of shielding as the other period 3s

Question 20

Explain why the second ionization energy of boron is higher then the first ionisation energy

Answer 20

As the electron is now being taken away from a positive ion

Question 21

how do TOF mass spectrometers separate two species to give two peaks

Answer 21

Positive ions are accelerated by an electric field
to a constant kinetic energy
the lighter ion will travel faster and so more of them will reach the detector first