Atomic Structure

Question 1

What is time of flight mass spectrometry used for?

Answer 1

-used to measure the relative mass of isotopes

-used in pharmaceutical/forensic/environmental analysis

Question 2

why is a vacuum required for mass spectrometry?

Answer 2

`so there’s no interference with air particles

Question 3

ToFMS Stage 1: Ionisation (Electrospray)

Answer 3

• sample is dissolved in a volatile polar solvent and injected through a needle at a high voltage
• Each particle gains a proton and becomes a 1+ ion

Question 4

ToFMS Stage 1: Ionisation (Electron Impact)

Answer 4

• high energy electrons are fired from an electron gun which knock off an electron each
• This forms 1+ ions

Question 5

what is the equation for an ion created by electrospray?

Answer 5

X₍₉₎ + H⁺ → XH⁺₍₉₎

Question 6

what is the equation for an ion created by electron impact?

Answer 6

X₍₉₎ → X⁺₍₉₎ + e⁻

Question 7

ToFMS Stage 2: Acceleration

Answer 7

-positive ions are accelerated by an electric field to a constant kinetic energy

-velocity depends on mass of the ion

Question 8

ToFMS Stage 3: Ion Drift

Answer 8

• ions go through a tube of known distance and time that it takes to reach the detector is recorded
• heavier ions take longer to reach detector
• lighter ions reach the detector faster

Question 9

ToFMS Stage 4: Ion Detection

Answer 9

• positive ions hit a negatively charged plate and pick up ab electron each
• this flow of electrons produces a current which is directly proportional to the abundance of the isotopes

Question 10

ToFMS Stage 5: Data Analysis

Answer 10

• the detector is linked to an amplifier and then to a recorder which converts the current into a peak that is shown in a mass spectrum
• the height of the peak is proportional to the abundance of ion

Question 11

what equation links the time or mass of an isotope to the time or mass of another

Answer 11

m1/(t1)^2=m2/(t2)^2

Question 12

How to work out mass of one 1+ particle

Answer 12

m = (mass number ÷ Avogadro’s Constant)/1000

Question 13

how would you find the Mr of a sample from the m/z values (TOF mass spectrometry) when doing electron impact ionisation

Answer 13

the Mr is equal to the peak with the greatest m/z value

Question 14

how would you find the Mr of a sample from the m/z values (TOF mass spectrometry) when doing electrospray ionisation

Answer 14

the Mr is equal to the peak with the greatest m/z value minus one

Question 15

what is the definition of relative atomic mass

Answer 15

The average mass of an atom of an element, relative to 1/12th of the mass of an atom of carbon-12

Question 16

how would you calculate relative atomic mass

Answer 16

sum of (isotope abundance x isotope number) / sum of isotope abundance

Question 17

what is the order of increasing energy of the energy sublevels

Answer 17

s→p→d→f

Question 18

how many orbitals does each sublevel (s,p,d,f) have

Answer 18

s - 1 orbital
p - 3 orbitals
d - 5 orbitals
f - 7 orbitals

Question 19

how many electrons does each sublevel (s,p,d,f) hold

Answer 19

s - 2 electrons
p - 6 electrons
d - 10 electrons
f - 14 electrons

Question 20

what is the order in which energy levels are filled

Answer 20

1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s ….

Question 21

why are electrons removed from energy level 4s before 3d

Answer 21

4s is lower in energy than 3d

Question 22

what are the exceptions to the standard electronic configuration

Answer 22

chromium
- 1s², 2s², 2p⁶, 3s², 3p⁶, 4s¹, 3d⁵
- more stable as a half subshell (3d⁵)

Copper
- 1s², 2s², 2p⁶, 3s², 3p⁶, 4s¹, 3d¹⁰
- more stable as a full subshell (3d¹⁰)