Atomic structure

Question 1

isotopes definition

Answer 1

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

Question 2

why do isotopes exist?

Answer 2

there can be different numbers of neutrons in the nucleus of atoms of each element

Question 3

what is the mass spectrometer used for

Answer 3

to identify elements and their relative molecular mass
relative isotopic mass
relative abundance of isotopes

Question 4

why is the mass spectrometer apparatus in a vacuum

Answer 4

to prevent ions colliding with air particles

Question 5

what are the 4 steps of mass spectrometry

Answer 5

1) ionisation
2) acceleration
3) ion drift through flight tube
4) ion detection

Question 6

names of the different methods of ionisation

Answer 6

electron impact and electrospray

Question 7

describe electron impact

Answer 7

sample is vaporised
electron gun fires high energy electrons at it
one electron from each particle is knocked off
forms a 1+ ion

Question 8

electron impact equation

Answer 8

X(g) + e- –> X+(g) + 2e-

Question 9

which elements/ substances is electron impact for and why

Answer 9

with low formula mass

molecular ion may break down into fragments

Question 10

describe electrospray

Answer 10

sample is dissolved in a volatile solvent and is injected through a hypodermic needle
positive terminal of a high voltage power supply is attached to the tip of the needle
particles gain a proton from the solvent
solvent evaporates away
leaves 1+ ions to accelerate towards the negative plate

Question 11

electrospray equation

Answer 11

X(g) + H+ –> XH+(g)

Question 12

which elements/ substances is electrospray used for

Answer 12

with higher molecular mass

Question 13

describe the acceleration process

Answer 13

positive ions are accelerated by an electric field
all have equal KE
ions with different masses have different velocities
lighter ions have higher velocities

Question 14

describe ion drift through flight tube process

Answer 14

positive ions travel through a hole in the negatively charged plate into a flight tube
ions with different masses seperate
time of flight of each ion depends on its mass

Question 15

describe ion detection process

Answer 15

positive ions hit a negatively charged electric plate
ions become discharged by gaining electrons
this movement of electrons generates an electric current which is measured
current is related to abundance

Question 16

why does the sample need to be ionised for mass spectrometry

Answer 16

for acceleration and detection

Question 17

what does the mass spectrum show

Answer 17

shows the mass tp charge ratio and abundance of each ion that reaches the detector

Question 18

relative atomic mass equation

Answer 18

= combined mass of all isotopes/ combined abundance of all isotopes

Question 19

first ionisation energy definition

Answer 19

the enthalpy change when an electron is removed from each atom in a mole of gaseous atoms to form one mole of 1+ gaseous ions

Question 20

equation for first ionisation energy

Answer 20

X(g) –> X+(g) + e-

Question 21

equation for n ionisation energy

Answer 21

X^(n-1)+(g) –> X^n+(g) + e-

Question 22

rule for which electron removed

Answer 22

highest energy electrons are lost first when an ion is formed

Question 23

are ionisation energy reactions endo or exothermic

Answer 23

endothermic

energy required to remove an electron by overcoming the forces of attraction between the e- and positive nucleus

Question 24

factors affecting ionisation energy (3)

Answer 24

distance between highest energy electron and nucleus
nuclear charge
shielding (repulsion) by electrons in inner shell between nucleus and outer shell electron

Question 25

trend of 1st ionisation energy down a group

Answer 25

requires less energy down a group

• more shielding as more energy levels
• further distance from nucleus

Question 26

general trend of 1st ionisation energy across a period

Answer 26

generally requires more energy

• increase in nuclear charge
• atoms become smaller so closer distance

Question 27

why is there a decrease in 1st ionisation energies from group 2-3

Answer 27

p orbital is higher in energy than s orbital

Question 28

why is there a decrease in 1st ionisation energies from group 5-6

Answer 28

extra electron-electron repulsion within orbital makes it easier to lose electron

Question 29

general trend for successive ionisation energies of an element

Answer 29

generally requires more energy for the next electron lost

• highest energy electrons become closer to the nucleus
• less shielding
• ions increases attraction with other electrons

Question 30

why are there some bigger jumps between some successive ionisation energies

Answer 30

more energy is required to remove electrons at the next energy level which is lower in energy

• less shielding
• increase ion charge
• closer distance

Question 31

rules for filling up energy levels

Answer 31

hunds rule
aufbau principle
paulis principle
4s is filled and emptied before 3d
Cr and Cu loses one electron from 4s to 3d
shorthand uses previous noble gas + additional electrons

Question 32

hund’s rule

Answer 32

electrons prefer to occupy orbital on their own (parallel spin) and only pair up (opposite spin) when no empty orbitals of the same energy level are available

Question 33

aufbau principle

Answer 33

electrons fill up lowest (sub)energy levels first

Question 34

pauli’s principle

Answer 34

each orbital holds a maximum of 2 electrons