1 Atomic structure

Question 1

What is the relative charge of a proton?

Answer 1

+1

Question 2

What is the relative mass of a proton?

Answer 2

1

Question 3

What is the relative charge of a neutron?

Answer 3

0

Question 4

What is the relative mass of a neutron?

Answer 4

1

Question 5

What is the relative charge of an electron?

Answer 5

-1

Question 6

What is the relative mass of an electron?

Answer 6

1/1836

Question 7

Define mass number (A)

Answer 7

The total number of protons and neutrons in the nucleus of an atom

Question 8

Define atomic (proton) number (Z)

Answer 8

The number of protons in the nucleus of an atom

Question 9

What are isotopes?

Answer 9

Atoms with the same number of protons, but different numbers of neutron

Question 10

Describe electron impact ionisation

Answer 10

The sample is vaporised

High energy electrons from an electron gun are fired at the sample

This knocks off one electron from each particle forming 1+ ions

X(g) → X+(g) + e-

Question 11

What is electron impact ionisation used for?

Answer 11

Elements and substances with low formula mass

eg Methane CH4(g) → CH4+(g) + e-

Question 12

Describe electrospray ionisation

Answer 12

The sample is dissolved in a volatile, polar solvent

And injected through a fine hypodermic needle to give a fine mist

The tip of the needle is attatched to the positive terminal of a high-voltage power supply

Particles gain a proton (H+) ion to form positive ions

X(g) + H+ → XH+ (g)

Question 13

What is electrospray ionisation used for?

Answer 13

Substances with higher molecular mass including many biological molecules such as proteins

This is known as a ‘soft’ ionisation technique and fragmentation rarely takes place

Question 14

Describe acceleration

Answer 14

The positive ions are accelerated using an electric field so that they all have the same kinetic energy

Question 15

What is the equation for kinetic energy?

Answer 15

KE = 1/2mv^2

KE = kinetic energy of particle (J)

m = mass of the particle (kg)

v = velocity of the particle (ms^-1)

Question 16

Describe ion drift (in the flight tube)

Answer 16

The positive ions travel through the mass spectrometer to the detector

Therefore lighter ions travel faster and reach the detector in less time than the heavier particles that move slower and take longer to reach the detector

Question 17

What is the equation for time of flight?

Answer 17

t = d/v

t = time of flight (s)
d = length of flight tube (m)
v = velocity of the particle (ms^-1)

Question 18

Describe detection

Answer 18

Each positive ion gains an electron

This generates a current

M+ + e- → M

The size of the current is proportional to the abundance of the ion

The greater the abundance, the higher the current

Question 19

Why must the sample be ionised?

Answer 19

So that it can be accelerated and detected

Question 20

Why is the whole spectrometer kept under vacuum?

Answer 20

To prevent ions colliding with molecules in the air

Question 21

How do you calculate the mass of an ion (kg)?

Answer 21

Relative isotopic mass x 10^-3 / 6.022 x 10^23

Question 22

How many electrons can principal quantum number 1 hold?

Answer 22

2

Question 23

How many electrons can principal quantum number 2 hold?

Answer 23

8

Question 24

How many electrons can principal quantum number 3 hold?

Answer 24

18

Question 25

How many electrons can principal quantum number 4 hold?

Answer 25

32

Question 26

How many electrons can an s sub-shell hold?

Answer 26

2

Question 27

How many electrons can an p sub-shell hold?

Answer 27

6

Question 28

How many electrons can an d sub-shell hold?

Answer 28

10

Question 29

How many electrons can an f sub-shell hold?

Answer 29

14

Question 30

What is the electron configuration of Chromium?

Answer 30

[Ar] 3d5 4s1

Question 31

What is the electron configuration of Copper?

Answer 31

[Ar] 3d10 4s1

Question 32

Define ionisation energy

Answer 32

The energy needed to remove one mole of electrons from one mole of atoms in the gaseous state

Question 33

Write an equation for the first ionisation energy of calcium

Answer 33

Ca(g) → Ca+ (g) + e-

Question 34

Write an equation for the second ionisation energy of titanium

Answer 34

Ti+ (g) → Ti2+(g) + e-

Question 35

What are the factors that influence first ionisation energies?

Answer 35

Size of the nuclear charge Distance of outer electrons from the nucleus Shielding effect of inner electrons

Question 36

Explain the trend in first ionisation energy across a period

Answer 36

General increase The e- to be removed is in the same shell, with similiar shielding There are more protons in the nucleus, so the attraction between the nucleus and the outer e- increases, so more energy is required

Question 37

Explain why there is a slight decrease in first ionisation energy between nitrogen and oxygen

Answer 37

In oxygen there is a pair of e- in a 2p orbital These repel so the e- is easier to remove

Question 38

Explain why there is a slight decrease in first ionisation energy between beryllium and boron

Answer 38

The electron being removed is in B in the 2p subshell Which is further away from the nucleus and so more shielded So there is less attraction between the nucleus and outer e-, less energy is needed to remove e-

Question 39

Explain why there is a large decrease in first ionisation energy from one period to the next

Answer 39

There is a large decrease There is increased shielding by inner electrons because of the added shell The attraction between the nucleus and outer e- is less, less energy is needed to remove e-

Question 40

Explain the trend in first ionisation energy down a group

Answer 40

Decreases Atomic radius increases, there are more shells so more shielding So the attraction between the nucleus and e- to be removed decreases, so less energy is required