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
