Section 1 - Atomic Structure

Question 1

Define Isotope

Answer 1

Atoms of the same element with different numbers of neutrons.

Question 2

Define Relative Atomic Mass

Answer 2

The average mass of an atom of an element on a scale where an atom of carbon-12 is 12.

Question 3

Define Relative Isotopic Mass

Answer 3

The mass of an atom of an isotope of an element on a scale where an atom of carbon-12 is 12.

Question 4

Define Relative Molecular Mass

Answer 4

The average mass of a molecule on a scale where an atom of carbon-12 is 12.

Question 5

What are the 4 stages of Mass Spectrometry?

Answer 5

1) Ionisation
2) Acceleration
3) Ion Drift
4) Detection

Question 6

What happens during Ionisation in Mass Spectrometry? (Two types)

Answer 6

Electrospray Ionisation - Sample is dissolved and pushed through a nozzle at a high pressure. High voltage applied causing each particle to gain a H+ ion. The sample is turned into a gas made up of positive ions.
Electron Impact Ionisation - Sample is vaporised and an electron gun is used to fire high energy particles at it. This knocks an electron off each particle so they become +1 ions.

Question 7

What happens during Acceleration in Mass Spectrometry?

Answer 7

The positively charged ions are accelerated by an electric field so that they all have the same kinetic energy.

Question 8

What happens during Ion Drift in Mass Spectrometry?

Answer 8

The ions enter a region with no electric field so they drift through it. They move at different speeds depending on their weights.

Question 9

What happens during Detection in Mass Spectrometry?

Answer 9

The detector detects charged particles and a mass spectrum is produced.

Question 10

Define Ionisation

Answer 10

The removal of one or more electrons.

Question 11

Define First Ionisation Energy

Answer 11

The energy needed to remove one electron from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions.

Question 12

Is ionisation exothermic or endothermic?

Answer 12

Endothermic

Question 13

What’s the general equation for first ionisation?

Answer 13

X(g) —> X+(g) + e-

Question 14

What’s the general equation for second ionisation?

Answer 14

X+(g) —> X2+(g) + e-

Question 15

What are the factors affecting Ionisation Energy?

Answer 15

1) Nuclear Charge
2) Distance from Nucleus
3) Shielding

Question 16

How does nuclear charge affect ionisation energy?

Answer 16

More protons = stronger attraction for electrons

Question 17

How does distance from nucleus affect ionisation energy?

Answer 17

Electrons closer to the nucleus will be much more strongly attracted than one further away

Question 18

How does shielding affect ionisation energy?

Answer 18

As number of electrons between outer electrons and nucleus increases, the attraction weakens.

Question 19

What does it mean if something has a high ionisation energy?

Answer 19

There’s a high attraction between the electron and the nucleus so more energy is needed to remove the electron.

Question 20

Define Second Ionisation Energy

Answer 20

The energy needed to remove 1 electron from each ion in 1 mole of gaseous 1+ ions to form 1 mole of gaseous 2+ ions.

Question 21

What is the trend in successive ionisation energies?

Answer 21

• Within each shell, it increases - electrons are being removed from an increasingly positive ion and there’s less repulsion among remaining ions so they’re held more strongly.
• Big jumps mean a new shell is being broken into - an electron is being removed from a shell closer to the nucleus

Question 22

How can you tell which group an element belongs to from its successive ionisation energies graph?

Answer 22

Number of electrons removed before first big jump = group number.

Question 23

When do you use Electron Impact?

Answer 23

During Ionisation in Mass Spectrometry for elements and low Mr compounds.

Question 24

When do you use Electrospray Ionisation?

Answer 24

During Ionisation in Mass Spectrometry for high Mr compounds.

Question 25

What’s the formula for Kinetic Energy?

Answer 25

1/2mv^2

Question 26

What’s the equation used to calculate time taken to reach the detector in Mass Spectrometry?

Answer 26

time = distance x square root(mass / 2 x kinetic energy)

Question 27

What happens when ions hit the detector in Mass Spectrometry?

Answer 27

A current is produced.

Question 28

Why are ions attracted to the detector in Mass Spectrometry?

Answer 28

The detector is negatively charged and the ions are positively charged - there is an attraction.

Question 29

How do you calculate Relative Atom Mass (Ar) using the mass spectrum?

Answer 29

Average mass of atoms = Total mass of all atoms/Total number of atoms

Question 30

How do you find the Mr of a compound from a Mass Spectrum?

Answer 30

The peak in the spectrum is equal to the relative molecular mass.

Question 31

What is the trend in First Ionisation Energies down a group?

Answer 31

It decreases.
Because:
-The extra inner shells shield the outer electrons from the attraction of the nucleus.
- The outer electrons are further from the nucleus.

Question 32

What is the trend in First Ionisation Energies across a period?

Answer 32

It increases.
Because:
- There are more protons, therefore a stronger attraction.
- All the extra electrons are at roughly the same energy level therefore there’s little shielding.

Question 33

Why is there a drop in First Ionisation Energy between group 2 and 3?

Answer 33

The element’s outer electron is in the 3p shell which has a slightly higher energy than the 3s so it is slightly further from the nucleus and has more shielding.

Question 34

Why is there a drop in First Ionisation Energy between group 5 and 6?

Answer 34

The shielding in the elements is equal but the Group 6 element loses its outer electron from an orbital containing two electrons and the repulsion between these electrons means they’re easier to remove.