P- A.S. =) Flashcards
Give evidence to support that the maximum number of e- that can be accommodated in the s-subshell is 2. (1)
2 elements before drop in IE to Al.
Explain why the m/z peak at 31.5 for copper is very small. (1)
- ↑ energy needed to removed 2nd e-
Explain how, in a mass spectrometer, ions are detected and how their abundance is measured. (3)
- ions collide w/ detector
- current flows
- abundance ∝ size of current
Define the term relative atomic mass. An element exists as a mixture of three isotopes.
Explain, in detail, how the relative atomic mass of this element can be calculated from data obtained from the mass spectrum of the element. (7)
- weighted av. mass of an atom of an element relative to 1/12th the mass of an atom of Carbon-12
- spectrum gives relative abundances
- and m/z
- m/z x relative abundances for each isotope
- add them tgt
- divide by sum of relative abundances
Explain the four main stages involved in obtaining the mass spectrum of a sample of gaseous titanium atoms.
Explain why it would be difficult to distinguish between 48Ti2+ and 24Mg+ ions using a mass spectrometer. (10)
- Ionisation
– high energy e-
– knocks e- off
– +ve ion - Acceleration
– electric field - Deflection
– by magnetic field - Detection
– current flows
- same m/z
- same deflection
Outline how the TOF mass spectrometer is able to separate these two species (m/z: 104 & 118) to give two peaks. (4)
- +ve ions accelerated by electric field
- to constant ke
- both ions have same m/z- 104 has higher speed
- 104 arrives at detector first
State and explain the trend in the first ionisation energies of the elements in Group 2 from magnesium to barium. (3)
- ↓
- ions get bigger
- ↓ attraction to outer e- ==> more easily lost
Explain how ions are accelerated, detected and have their abundance determined in a time of flight mass spectrometer. (3)
- acceleration- attracted to a -ve plate
- detected by gaining e-
- abundance proportional to size of current
Explain why the second ionisation energy of calcium is lower than the second ionisation energy of potassium. (2)
- Ca: outer e- further form nucleus
- // e- lost from a higher energy orbital
- ↑ SHIELDING
Give one reason why the second ionisation energy of silicon is lower than the second ionisation energy of aluminium. (1)
Si:
- e- removed from 3p
- ↑ in energy
- ↑ shielded
Predict the element in period 3 that has the highest second ionisation energy.
Explain why. (2)
/
Period 3: Na Mg Al Si P S Cl Ar
- Na
- e- removed from 2p
Explain why the ionisation energy of every element is endothermic. (1)
- Energy needed to overcome
- attraction between -ve e- & +ve nucleus
Identify the s-block metal that has the highest first ionisation energy. (1)
Beryllium
x Li ∵ Be has ↑ nuclear charge but x extra shielding
Describe how the molecules are ionised using electrospray ionisation. (3)
- sample dissolved in volatile solvent
- injected thru +ve ly charged needle at high voltage
- each molecule gains a proton
State how the relative abundance of 185Re+ is determined in a TOF mass spectrometer. (2)
- ion gains an e- at detector
- relative abundance depends on size of current
The mass spectrum of the element phosphorus has a peak at m/z = 124.
Give the formula of the species responsible for this peak.
(2)
³¹P₄ +
Which atom has the greatest first ionisation energy?
[1 mark]
A H
B He
C Li
D Ne
B
Identify the element in Period 3, from sodium to argon, that has the highest second ionisation energy. (1)
Na!!!!!!
Electrospray ionisation is used instead of electron impact for the ionisation of a protein in a mass spectrometry experiment.
Suggest why. (1)
protein x break up/ fragment
