mass spectrometry and ionisation energy

Question 1

isotopes

Answer 1

atoms with the same number of protons but different number of neutrons

Question 2

why do isotopes react the same way chemically?

Answer 2

they have the same number of electrons

Question 3

mass spectrometer

Answer 3

machine that measures the mass of atoms/molecules to find their Mr or Ar
- very accurate
-can identify elements

Question 4

relative atomic mass

Answer 4

average mass of an atom/ 1/12 the mass of a 12C atom

Question 5

relative molecular mass

Answer 5

average mass of one molecule/ 1/12 mass of a 12C atom

Question 6

steps of TOF mass spectrometer

Answer 6

1. vaporisation
2. ionisation
3. acceleration
4. ion drift
5. detection

Question 7

vaporisation

Answer 7

sample is vaporised so it can travel through the spectrometer

Question 8

electron impact ionisation

Answer 8

sample is vaporised;
high energy e- are fired at it from an electron gun;
causes sample to lose e-
used for elements with low Mr and molecular ion usually breaks down into smaller fragments

Question 9

electrospray ionisation

Answer 9

sample is dissolved in water/methanol;
injected through a fine hypodermic needle & high voltage is applied
loses electron to becomes positive and is attracted to negative plate for acceleration
used for molecules with higher Mr

Question 10

acceleration

Answer 10

positive ions are accelerated using an electric field so that they have the same kinetic energy
heavier particles travel slower, lighter particles travel faster

Question 11

ion drift

Answer 11

positive ions travel through a tube before reaching the detection plate

Question 12

detection

Answer 12

positive ions hit a negatively charged electric plate;
the positive ions gain electrons from the plate, generating movement and therefore an electric current
the more ions that hit the plate the bigger the current and the size of the current gives a measure of the number of ions hitting the plate

Question 13

fragmentation

Answer 13

when the loss of an electron leads to a weaker covalent bond, so an atom is lost
e.g. C2H6O->C2H6O+->C2H5O

Question 14

formula for relative atomic mass

Answer 14

(abundanceAr)+(abundanceAr)/total abundance

Question 15

how many g in 1 mol of O

Answer 15

Ar: 16
mass: 16g

Question 16

how do you identify between the isotopes of an element on an m/z graph

Answer 16

ions with different isotopes produce different signals

Question 17

relative atomic mass def

Answer 17

the average mass of an atom of an element relative to 1/12th the mass of an atom of 12C

Question 18

relative molecular mass def

Answer 18

the average mass of one molecule of an element or compound relative to 1/12th the mass of an atom of 12C

Question 19

relative isotopic mass def

Answer 19

the mass of an atom of an isotope relative to 1/12th of the mass of a 12C atom

Question 20

m/z

Answer 20

mass of an isotope/charge

Question 21

peak

Answer 21

peaks show fragments of the original molecule; last peak is the m+1 (same as Mr)

Question 22

ionisation energy

Answer 22

minimum amount of energy required to remove 1 mol of e- from 1 mol of atoms in the gaseous state

Question 23

shielding

Answer 23

weaker attraction between outer electron and nucleus when there are more electron shells

Question 24

value of ionisation energy

Answer 24

endothermic so always +ve

Question 25

nuclear charge

Answer 25

higher attraction when there are more protons in the nucleus and the same amount of shielding

Question 26

atomic size

Answer 26

weaker attraction to the nucleus when the atoms are larger

Question 27

successive ionisation energies

Answer 27

removal of the next electron; general increase in energy as e- is removed from a more positive ion; jump in energy as e- are removed from shell closer to nucleus

Question 28

first ionisation energy down the group

Answer 28

decreases; atomic radius increases - valence electron is further away from the nucleus; shielding increases- more shells between nucleus and valence electron so less energy is required;

Question 29

first ionisation energy across a period

Answer 29

general increase; increasing nuclear charge - increase in number of protons which increases attraction; shielding stays the same - distance from nucleus decreases

Question 30

dip between Mg and Al

Answer 30

Al's outer electron is in the 3p subshell and Mg's electron is in 3s subshell; weaker attraction between Al's outer electron and the nucleus; less energy required to remove electron

Question 31

dip between P and S

Answer 31

S's valence electron shares an orbital; electrons repel each other; less energy required to remove electron