1. Atomic structure (MASS SPECTROMOTERY)

Question 1

Give the relative mass and charge of protons, electrons and neutrons

Answer 1

Particles Relative mass Charge
Proton: 1 + 1
Neutron: 1 0
Electron: 1/1840 -1

Question 2

Define nucleons

Answer 2

Total number of protons and neutrons in an atoms nucleus

Question 3

Define atomic (proton) number

Answer 3

Number of protons in the nucleus
–> given the letter Z

Question 4

Define mass number

Answer 4

Number of protons and neutrons in an atom
–> given the letter A

Question 5

Define isotope

Answer 5

Atoms of the same element with the same number of protons but different number of neutrons

Question 6

Define relative isotopic mass

Answer 6

The average mass of an atom of an isotope relative to one twelfth of the mass of one atom of carbon -12

Question 7

Define relative atomic mass (Ar)

Answer 7

The average mass of an atom of an element relative to one twelfth of the mass of one atom of carbon -12

Question 8

Uses of mass spectrometry

Answer 8

1) identifying elements on other planets and their isotopes
2) drug testing in sports to identify chemicals in the blood
3) quality control in the pharmaceutical industry
4) radioactive dating (carbon - 14) to determine age of fossils etc.

Question 9

Give the 4 stages of mass spectrometry

Answer 9

Ionisation
Acceleration
Deflection
Detection

Question 10

Describe stage one of mass spectrometry

Answer 10

Ionisation - Heated metal coil gives off electrons that are attracted to the positively charged plate above it. Gaseous sample is bombarded by electrons to form 1+ ions.

Question 11

Describe stage two of mass spectrometry

Answer 11

Accelerated using an electric field

Question 12

Describe stage 3 of mass spectrometry

Answer 12

Charged particles deflected by a magnetic field - with an electromagnet

Question 13

What does the size of deflection in mass spectrometry depend on

Answer 13

Mass of ion - lighter ions are deflected more than heavier ones
Charge on the ion- 2+ ions are deflected more than a +1 ion. This halves the m/z (mass/charge) value but the abundance stays the same.

Question 14

What does the m/z ratio show

Answer 14

The mass of the isotope
–> mass / charge but charge is often just +1 so its just mass

Question 15

Describe stage 4 of mass spectrometry

Answer 15

The beam of ions passing through the machine is detected electrically.
–> when the beam of ions hits a negative plate its charge is neutralised by an electron jumping from the metal on to the ion. That leaves a space amongst the electrons in the metal, and the electrons in the wire shuffle along to fill it.

–> A flow of electrons in the wire is detected as an electric current which can be amplified and recorded. The more ions arriving, the greater the current.

Question 16

What does the mass spectrum for monatomic elements show

Answer 16

Lines represent different isotopes in that element

Question 17

What is fragmentation

Answer 17

When a molecule becomes ionised to form a molecular ion (M+) which is unstable and can fragment into different pieces

Question 18

what does the mass spectrum for a molecule with different atoms show

Answer 18

It shows the different fragments produced when the molecular ion breaks up

Question 19

Describe the mass spectrum for chlorine.

Answer 19

In the ionisation chamber, an electron is knocked off the molecule to form a molecular ion - Cl2+. This can then form a chlorine atom and cl+ ions. As the atom has no charge it is not included in mass spectra. The cl+ atom will form lines at 35 and 37 in the ratio 3:1. However, you will also get lines for the unfragmented (cl2) +. This ion could either be from the isotopes:
chlorine 35 and chlorine 35
chlorine 35 and chlorine 37
chlorine 37 and chlorine 37
Therefore, you get lines in the ratio: 9:6:1

Question 20

Which peak is the molecular ion

Answer 20

M+ ion is the heaviest so it is furthest to the right

Question 21

What does the molecular ion peak ( M+) show on a mass spec

Answer 21

The relative molecular mass of the molecule

Question 22

Why must a vacuum be used in a mass spectrometer

Answer 22

no interference from atoms or molecules in air
- Molecular fragments could not exist otherwise

Question 23

When calculating relative atomic mass using the mass spectra, do you always divide by 100

Answer 23

No, not always. You divide by the total abundance which is not always 100%. Check by adding up total abundance either from a table or graph

Question 24

Give the equation to work out relative atomic mass

Answer 24

(isotopic mass x abundance) + (isotopic mass x abundance)…..
/
total abundance ( normally 100 but not always)

Question 25

How is emission spectra evidence for quantum shells?

Answer 25

1) the radiation emitted has a fixed frequency
2) electrons can only exist in shells, not between them
3) each shell has a fixed energy
4) defined lines of emission spectra prove electrons exist in shells only and not in between

Question 26

Describe how you would predict a mass spectra

Answer 26

1) Write the % of each isotope given as a decimal
2) Write the different combinations of the isotope and times the now decimal abundances
3) Divide the abundances by the smallest value to get a whole number ratio which can be used to predict the spectra