1.1 - 1.6 Atomic structure

Question 1

Relative atomic mass =

Answer 1

(isotope mass x abundance) + (isotope mass x abundance) / Total abundance

Question 2

Potential energy (J) =

Answer 2

charge(Q) x voltage(v)

Question 3

Kinetic energy (J) =

Answer 3

1/2 x mass (kg) x [velocity(m/s)]^2

Question 4

Velocity (m/s) =

Answer 4

distance(m) / time(s)

Question 5

What are the relative mass and charges of the 3 sub-atomic particles?

Answer 5

Particle / Relative mass / Relative charge
Proton / 1 / +1
Neutron / 1 / 0
Electron / Negligible / -1

Question 6

What is the name of the force that attracts protons and neutrons together in the nucleus?

Answer 6

Nuclear force

Question 7

What is the name of the force that attracts protons and electrons?

Answer 7

Electrostatic attraction

Question 8

Describe the development of the atomic model

Answer 8

1803 - John Dalton, recognised atoms of particular elements differ from other elements

1904 - J.J Thomson, discovered electrons and established plum-pudding model

1911 - Ernest Rutherford, gold and alpha particles experiment discovers nucleus

1913 - Niels Bohr, proposed stable electron orbits

1926 - Erwin Schrodinger, discovered orbitals

1932 - James Chadwick, discovered neutrons

Question 9

What is the purpose of mass spectometery?

Answer 9

To find out the relative atomic mass, relative molecular mass and relative abundances of isotopes

Question 10

What are the four stages of mass spectometery?

Answer 10

1. Ionisation
2. Acceleration
3. Ion drift
4. Detection

Question 11

What are the 2 types of ionisation?

Answer 11

• Electron impact ionisation
• Electrospray ionisation

Question 12

Describe electron impact ionisation

Answer 12

1. Sample vaporised
2. Electron gun fires high energy electrons at it
3. Knocks 1 electron off each atom (the outermost electron)
4. Forms positive ion
   This method often causes fragmentation

Question 13

Describe electrospray ionisation

Answer 13

1. Sample dissolved in polar solvent
2. Sample gains protons
   M + H+ –> MH+
3. Pumped through capillary needle
4. Voltage applied
5. Causes aerosol to be formed
6. Solvent evaporates and leaves MH+ ions
   This method does not cause fragmentation

Question 14

Describe the process of acceleration in mass spectometery

Answer 14

• An electrical field is applied to a series of plates
• This gives the same kinetic energy to all the ions
• Ions with a lower m/z ratio (lighter ions) will be accelerated more than those with higher m/z

(Attracted to negative plate)

Question 15

Describe the process of ion drift in mass spectometery

Answer 15

• All the ions leave the electrical field with equal kinetic energy
• In the drift region, lighter ions travel faster than heavier ions
• Deflected by electromagnet

Question 16

Describe the process of detection in mass spectometery

Answer 16

• Ions hit detector and gain electrons, generating a current
• The computer records the length of time it took the ion to pass through the machine and its abundance and uses this to create a mass spectrum

Question 17

What does an m/z peak on a mass spectrum mean if electron impact ionisation has been used?

Answer 17

m/z peak = Mr of molecule

Question 18

What does an m/z peak on a mass spectrum mean if electrospray ionisation has been used?

Answer 18

m/z peak = Mr of molecule + 1

Question 19

What is the maximum number of electrons each energy level can hold?

Answer 19

Energy level Max no. of electrons
1 2
2 8
3 18
4 32

Question 20

What is the Aufbau Principle?

Answer 20

An electron will always fill the available orbital of the lowest energy

Question 21

What is the Pauli Exclusion Principle?

Answer 21

Each orbital can hold a maximum of 2 electrons

Question 22

What is Hund’s rule?

Answer 22

Atomic orbitals of the same energy fill singly with electrons of the same spin before pairing of electrons occurs

Question 23

Define ionisation energy

Answer 23

The energy required to remove 1 mole of electrons from 1 mole of an element in its gaseous state

Question 24

What is the trend in ionisation energy going down the group?

Answer 24

Decreases because:
- More protons/larger nuclear charge
HOWEVER
- Bigger atomic radius
- More shielding
This means weaker attraction between the nucleus and electrons so less energy is required to remove an electron

Question 25

What is the trend in ionisation energy going across a period?

Answer 25

Increases because:
- Smaller atomic radius
- More protons/stronger nuclear charge
- Same shielding
This means stronger attraction between the nucleus and electrons so more energy is required to remove an electron

Question 26

Explain the dip in ionisation energies between the 2nd and 3rd group

Answer 26

The outermost electron comes from the P orbital which is slightly further away from the nucleus so the electron can be removed more easily. P-orbital is higher energy and more shielded.

Question 27

Explain the dip in ionisation energies between the 5th and 6th group

Answer 27

The 1st and 4th electrons in the 3p orbital are paired. As they are both negatively charged they slightly repel each other, meaning it requires less energy to remove one.

Question 28

Describe the equation for calculating Ar from a mass spec

Answer 28

(m/z x abundance) + (m/z x abundance) / total abundance

Question 29

State what is adjusted in a mass spectrometer in order to direct ions with different values onto the detector

Answer 29

Electromagnet. This is maintain the correct link between deflection and m/z.

Question 30

What would cause an ion to form a mass spec peak at half the expected m/z value?

Answer 30

The formation of a 2+ ion.
For example, 72Ge2+ peaks at 36.

Question 31

Which device in a mass spec ionises particles?

Answer 31

Electron gun

Question 32

What factors determine how much a particle is deflected in a magnetic field of given strength?

Answer 32

• m/z
• Speed

Question 33

Give three reasons why ionisation is necessary

Answer 33

To allow ions to be:
- accelerated (by an electric field)
- deflected (by a magnet/magnetic field)
- detected / description of current formed at the detector/sensor

Question 34

Explain why it would be difficult to distinguish between 48Ti2+ and 24Mg+ ions using a mass spectrometer

Answer 34

• Both ions have the same m / z value (of 24)
• Deflected equally (so detected together)