atomic structure

Question 1

what is the relative charge of a proton

Answer 1

+1

Question 2

what is the relative charge of a neutron

Answer 2

0

Question 3

what is the relative charge of an electron

Answer 3

-1

Question 4

what is the relative mass of a proton

Answer 4

1

Question 5

what is the relative mass of a neutron

Answer 5

1

Question 6

what is the relative mass of an electron

Answer 6

1/1840

Question 7

definition of atomic number

Answer 7

is the number of protons in the nucleus.

Question 8

definition of mass number

Answer 8

is the total number of protons and neutrons in the atom

Question 9

what is an isotope

Answer 9

Isotopes are atoms with the same number of protons, but different numbers of neutrons.

Question 10

what condition does a mass spectrometer have to be under to work

Answer 10

under a vacuum otherwise air particles would ionise and register on the detector

Question 11

what is the first step in time of flight mass spectrometer

Answer 11

ionisation

Question 12

what happens during ionisation

Answer 12

The sample can be ionised in a number of ways. Two of these techniques are electron impact and electrospray ionisation

Question 13

what is the method for electron impact ionisation

Answer 13

• A vaporised sample is injected at low pressure
• An electron gun fires high energy electrons at the sample
• This knocks out an outer electron
• Forming positive ions with different charges E.g. Ti (g)Ti+ (g)+ e–

Question 14

why would electron impact ionisation be used

Answer 14

is used for elements and substances with low formula mass. Electron impact can cause larger organic molecules to fragment.

Question 15

what is the method for electro spray ionisation

Answer 15

• The sample is dissolved in a volatile, polar solvent
• injected through a fine needle giving a fine mist or aerosol
• the tip of needle has high voltage
• at the tip of the needle the sample molecule, M, gains a proton, H+, from the
solvent forming MH+
• The solvent evaporates away while the MH+ ions move towards a negative plate

Question 16

why would electro spray ionisation be used

Answer 16

is used preferably for larger organic molecules. The ‘softer’ conditions of this technique mean fragmentation does not occur.

Question 17

what is the second step in in time of flight mass spectrometer

Answer 17

Acceleration

Question 18

what happens during acceleration

Answer 18

•Positive ions are accelerated by an electric field •To a constant kinetic energy
KE = 1⁄2mv2

Question 19

if all the particles have the same kinetic energy what does the velocity depend on

Answer 19

The mass

the lighter particles will move faster than the heavier particles

Question 20

what is the 3rd step in time of flight mass spectrometer

Answer 20

flight tube

Question 21

what happens in the flight tube stage

Answer 21

• The positive ions with 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 22

what is the equation for the flight tube

Answer 22

t=d/v
d= distance
v= velocity

Question 23

what is the 4th step in time of flight mass spectrometer

Answer 23

detection

Question 24

what happens in detection

Answer 24

The ions reach the detector and generate a small current, which is fed to a computer for analysis. The current is produced by electrons transferring from the detector to the positive ions.