Atomic Structure (Relative mass, Mass Spectrometry, Ionisation Energies)

Question 1

What 3 particles are found in an atom? Where in the atom are they loctated?

Answer 1

Protons, neutrons and electrons. The protons and neutrons are found in the nucleus. The electrons whizz around the nucleus in orbitals and take up most of the volume of the atom.

Question 2

What are the charges on the particles in an atom?

Answer 2

Proton = +1
Neutron= 0
Electron= -1

Question 3

Define Mass Number

Answer 3

The total number of protons and neutrons in the nucleus of an atom.

Question 4

Define Atomic Number

Answer 4

The number of protons in the nucleus of an atom.

Question 5

Define Isotope

Answer 5

Isotopes of an element are atoms with the same number of protons but a different number of neutrons.

Question 6

Define Relative Atomic Mass

Answer 6

The ratio of the average mass of one atom of that element to 1/12th of the mass of one atom of carbon-12.

Question 7

Define Relative Isotopic Mass

Answer 7

The ratio of the mass of one atom of that isotope to 1/12th of the mass of one atom of carbon-12.

Question 8

What are the four stages of mass spectrometry?

Answer 8

Electrospray ionisation, Acceleration, Ion Drift and Detection.

Question 9

What happens in ‘electrospray ionisation’?

Answer 9

The sample is dissolved in a polar solvent and pushed through a small nozzle at high pressure. A high voltage is applied, causing the particles to lose a electron. The ionised particles are then seperated from the solvent, leaving a gaseous sample of ions.

Question 10

What happens in ‘acceleration’?

Answer 10

The positive ions are accelerated by an electric field, smaller ions have a higher speed than larger ions.

Question 11

What happens in ‘ion drift’?

Answer 11

Ions leave the electric field at different speeds depending on their mass/charge ratio. The heavier the particle, the lower the speed and the greater the time taken to reach the detector.

Question 12

What happens in ‘detection’?

Answer 12

The ions create a current when they reach the detector. The detector records the time taken to reach it and the current. The greater the abundance of the isotope, the larger the current.

Question 13

How can you determine the relative molecular mass from the mass spectrum of a molecule?

Answer 13

The relative molecular mass of a molecule is obtained by looking at the peak in the spectrum with the largest m/e ratio (i.e the peak furthest to the right).

Question 14

Define ‘First Ionisation Energy’

Answer 14

The energy required to remove one electron from one mole of free gaseous atoms of that element.

Question 15

What is the trend in ionisation energies across a period? Why?

Answer 15

In general, the first ionisation energy increases across a period because the nucleur charge increases but the seiding remains the same.

Question 16

What is the trend in ionisation energies down group 2 to group 3? Why?

Answer 16

Ionisaton energies decrese group 2 to group 3 because in group 3 the electrons are removed from the p-orbital, so it is sheilded by the s-electrons in the outer shell. so the effecive nuclear charge decreases.

Question 17

Summarise the trend in first ionisation energies across period 2.

Answer 17

There is a general increase across the period as the nuclear charge increases and the sheilding remains the same.
There is a drop from Be to B because in B a 2p electron is being removed and he extra shielding from the 2s subshell causes a fall in the effective nuclear charge.
There is also a drop from N to O because the electron in O is being removed from a paired orbital. The repulsion of the electrons in this orbital makes them less stable and easier to remove.

Question 18

Define ‘Second Ionisation Energy’

Answer 18

The energy required to remove one electron from one mole of free gaseous unipositive ions.