1.Atomic Structure

Question 1

Define relative atomic mass

Answer 1

Average mass of an atom relative to 1/12th mass of a carbon-12 atom

Question 2

Define relative molecular mass

Answer 2

Average mass of a molecule relative to 1/12th mass of a carbon-12 atom

Question 3

What are the steps in TOF mass spectrometry

Answer 3

• ionisation
• acceleration
• ion drift
• detection

Question 4

Describe the steps in TOF mass spectrometry

Answer 4

-ionisation
-acceleration- + ions are attracted to - charged plate and accelerate towards it. Lighter ions travel faster.
Ion drift- ions pass through hole in - charged plate, called flight tube to the detector
Detection- flight times of each ion is recorded, + ions pick up electrons from the detector causing currently to flow

Question 5

Describe electron impact ionisation

Answer 5

-sample is vaporised
-high energy electrons fired from an electron gun.
-this knocks off one electron from each ion forming +1 ions.
X(g) + e- ——-> X+(g) + 2e-

Question 6

Describe electrospray ionisation

Answer 6

• the sample is dissolved in a volatile solvent
• then forced through a fine hollow needle which is connected to a + terminal
• produces tiny + charged droplets that have gained a proton
• solvent evaporates

Question 7

Why is the TOF mass spec kept under vacuum

Answer 7

To prevent the ions that are produced colliding with molecules from the air.

Question 8

Name the two kinds of ionisation used in TOF mass spec

Answer 8

• electrospray ionisation

- electron impact ionisation

Question 9

What is the electron arrangement for Cu (29)

Answer 9

1s2, 2s2, 2p6, 3s2, 3p6, 4s1, 3d10

Question 10

What is the electron arrangement for Cr (24)

Answer 10

1s2, 2s2, 2p6, 3s2, 3p6, 4s1, 3d5

Question 11

Why are the electron arrangements for Cu and Cr different

Answer 11

The atom is more stable when sub-levels are filled or half filled when compared to partially filled sub-levels.

Question 12

Define ionisation energy

Answer 12

Energy required to remove one mole of electrons from an atom in a gaseous state.

Question 13

Describe the first ionisation energy trend across a period

Answer 13

• across a period the first ionisation energy increases increases
• when you move across a period nuclear attraction increases
• no extra shielding
• more energy is required to remove an electron

Question 14

Why is there a drop in first ionisation energies between groups 2&3 and 5&6 across a period

Answer 14

• in group 3 the first electron is in a higher electron level meaning there is more shielding so less nuclear attraction compared to group 2’s first electron
• in group 5 all electrons in the p orbital are not paired whereas in group 6 one is paired. The repulsion between these paired electrons means less energy is needed to remove it

Question 15

Describe the trend of ionisation energies down a group

Answer 15

• nuclear attraction increases
• however the effect of more shielding is stronger
• meaning overall it decreases

Question 16

What forces hold together protons and neutrons in the centre of an atom

Answer 16

strong nuclear force

Question 17

What forces hold electrons and protons together in an atom

Answer 17

electrostatic forces

Question 18

What is the atomic number

Answer 18

number of protons

Question 19

What is the mass number

Answer 19

number of protons + neutrons

Question 20

Electrons in the same orbital must have..

Answer 20

opposite spins