1 Atomic Structure

Question 1

Describe what is meant by relative atomic mass

Answer 1

• the average mass of an atom of an element relative to 1/12 of the mass of an atom of carbon-12.

Question 2

Describe what is meant by relative molecular mass

Answer 2

• The average mass of a molecule relative to 1/12 of the mass of an atom of carbon-12

Question 3

Describe what is meant by relative isotopic mass

Answer 3

• The average mass of an atom of a particular isotope relative to 1/12 of the mass of an atom of carbon-12

Question 4

Why do isotopes have similar chemical properties but varying physical properties

Answer 4

• Isotopes have similar chemical properties because they have the same electron configuration
• Isotopes are varying physical properties because they have different masses

Question 5

Describe what is meant by electron configuration

Answer 5

• Electron configuration refers to the arrangement of electrons in the energy levels, sub levels and orbitals

Question 6

Why is the 3D sub level filled after the 4S sub-level

Answer 6

• 3d is higher in energy then 4s, so 4s is filled first and then 3d is filled
• Once 3d is filled, 4s is no longer lower in energy, so 4s electrons are lost first since they are further away from the nucleus

Question 7

Describe what is meant by first ionisation energy

Answer 7

The energy required to remove 1 mole of electrons from 1 mole of atoms of an element to form 1 mole of 1+ ions

Question 8

Describe what is meant by second ionisation energy

Answer 8

The energy required to remove the 2nd mole of electrons from each 1+ ion, to form one mole of 2+ ions

Question 9

Why are excessive ionisation energies always higher

Answer 9

Positive ion is formed by the first ionisation energy, meaning that the nuclear charge is higher, therefore it is harder for the second electron to be removed since there is a stronger attraction between the electron and the nucleus

Question 10

How do you identify an element just bytes ionization energy graph

Answer 10

The ionisation energy number on the x-axis before there is a big jump = electrons in outer shell

Question 11

What’s the four steps in time of flight mass spectrometry

Answer 11

• Ionisation
• Acceleration
• Ion drift
• Detection

Question 12

What are the two types of ionisation in mass spectrometry

Answer 12

• Electron impact and
• Electrospray ionisation

Question 13

Describe the stages of electron impact

Answer 13

• High energy electrons are fired at the sample using an electron gun
• This knocks off an electron to form a one plus ion

Question 14

Describe the process of electrospray ionisation

Answer 14

• The sample is dissolved in a volatile solvent, and injected through a fine hypodermic needle as a spray into the ionisation chamber
• The needle is attached to the positive terminal of a high voltage power supply
• As a spray emerges from the end of the needle the particles gain a proton from the positive charge of the supply
• The solvent evaporates leaving the 1+ ions

Question 15

When would you use a two types of ionization

Answer 15

• Electron impact is used for elements and low Mr compounds
• Electrospray ionisation is used for high Mr compounds

Question 16

Describe what happens during acceleration

Answer 16

The positive ions are attracted to the negatively charged plate and Accelerate towards it

Question 17

Describe what happens during ion drift

Answer 17

Ions pass through a hole in the negatively charged plate, form a beam and travel along the flight tube

Question 18

Describe what happens during detection

Answer 18

• Lighter ions arrive at the detector first as they have a lower m/z ratio.
• Flight times are recorded comma and the positively charged ions pick up an electron from the detector, causing a current flow

Question 19

What does the mass spectrometer determine

Answer 19

• m/z
• Relative abundance

Question 20

What necessary conditions are required in the TOF mass spectrometer

Answer 20

• Kept under a vacuum so that ions do not collide with air molecules
• Gaseous state

Question 21

Describe how to calculate the average relative atomic mass

Answer 21

Abundance X mass number / total abundance

Question 22

What’s equations on needed in TOF calculations

Answer 22

Avogadro’s constant = 6.022x10^23
KE= 1/2 x m x v^2
v=d/t
mass= mass number/6.022x10^23 ÷1000
v=√2KE/m

Question 23

Describe what happens to the ionisation energy as you go down a group

Answer 23

As you go down a group Thsation gy decreases because:
- atomic radius increases
- more shielding
- distance between the nucleus and electron
increases
- weaker attraction between the nucleus and outer electron
- less energy is required to remove an electron

Question 24

Describe what happens to the ionisation energy as you move across a period

Answer 24

The ionisation energy increases because:
- same shielding
- decreased atomic radius
- more protons
- increased nuclear charge
- stronger attraction between nucleus and electrons
- more energy required to remove an electron

Question 25

Describe what happens when an element ends in 2p4 or 3p4

Answer 25

• repulsion occurs
• therefore less energy is required to remove an electron

Question 26

What’s so special about chromium and copper

Answer 26

• Chromium and copper do not have the expected electron structure
• this is because the 3d orbital gets filled before the 4s Orbital