Atomic structure 1.1

Question 1

why do isotopes have similar chemical properties

Answer 1

the same electronic configuration

Question 2

what are the 4 steps in a mass spectrometer

Answer 2

1) ionisation ( electron impact and electro spray)
2) acceleration
3) flight tube
4) detection

Question 3

what is the process of electron impact ionisation

Answer 3

• a vaporised sample is injected at low pressure
• an electron gun fired high energy electrons at the sample
• this knocks out an outer electron
• forming positive ions with different charges

Question 4

what is the process of electro spray ionisation

Answer 4

• sample is dissolved in volatile solvents
• injected through a fine needle giving it a fine mist
• tip of needle has high voltage
• sample molecule gains a proton
• M(g) + H+ => MH+(g)
• The solvent evaporated away the MH+ ions towards a negative plate

Question 5

when would electron impact be used

Answer 5

for elements with low formula mass .
Can cause larger organic molecules to fragment

Question 6

when would you use electro spray ionisation

Answer 6

for larger organic molecules .
The softer conditions of this technique means fragmentation does not occur

Question 7

what is the process of acceleration

Answer 7

• positive ions are accelerated by an electric field
• to a constant kinetic energy
• the velocity of each particle depends on its mass
• lighter particles have a faster velocity

Question 8

what is the process of the flight tube

Answer 8

• the positive ions with the smaller m/z values will have the same kinetic energy as those with larger m/z and will move faster
• the heavier particles take longer to move through the drift area
• the ions are distinguished by different flight times

Question 9

what is the process of detection

Answer 9

• the ions reach the detector and generate a small current.
• the current is produced by electrons transferring from the detector to the positive ions

Question 10

what is the abundance of the species proportionate to

Answer 10

the size of the current

Question 11

what is the relative atomic mass formula

Answer 11

= sum of ( isotopic mass x %abundance) / 100

Question 12

what is the relative atomic mass formula if relative abundance is used instead of percentage abundance

Answer 12

sum of ( isotopic mass x relative abundance ) / total relative abundance