Chapter 1 (Atomic Structure)

Question 1

How are electrons and protons held together in an atom?

Answer 1

Electrostatic forces

Question 2

What are isotopes and how do they react?

Answer 2

Atoms with the same number of protons but different number of neutrons (same atomic number but different mass number). They react in the chemically in the same way as other atoms of the same element as they have the same electron configuration.

Question 3

What is a half-life?

Answer 3

The amount of time it takes for half of an atoms radioactivity to decay.

Question 4

How is carbon-14 decayed?

Answer 4

By cosmic-ray activity in the atmosphere.

Question 5

What is useful about the decay of carbon isotopes?

Answer 5

It can be used to find the age of organic matter unto 60,000 years old (most accurate unto 2000 years old).

Question 6

How does the level of carbon-14 change in living matter?

Answer 6

It remains constant as carbon is taken in through food and released through carbon dioxide until the organism dies.

Question 7

What is the formula for relative atomic mass?

Answer 7

average mass of 1 atom ÷ 1/12 mass of one atom of C¹²

Question 8

What does the mass spectrometer determine?

Answer 8

The mass of separate atoms

Question 9

What is the formula for relative molecular mass?

Answer 9

average mass of molecule ÷ 1/12 mass of 1 atom of C¹²

Question 10

How do mass spectrometers work?

Answer 10

Use the principle of forming ions from the sample and the separating the ions according to the ratio of their charge to their mass.

Question 11

What happens in a time of flight mass spectrometer?

Answer 11

The substance(s) in the sample are converted to positive ions, accelerated to high speeds (which depends on their mass to charge ratio), and arrive at a detector.

Question 12

Why is a vacuum used in a TOF instrument?

Answer 12

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

Question 13

Describe electrospray ionisation

Answer 13

A sample is dissolved in a volatile solvent and forced through a fine hollow needle which is connected to the positive terminal of a high voltage supply.

This produces tiny positive charged droplets that have gained a proton from the solvent.

The solvent evaporates from the droplets into the vacuum and the droplets get smaller and smaller until they contain only a single, positively charged ion.

Question 14

Describe electron impact

Answer 14

A sample is vaporised and high energy electrons are fired at it from an electron gun, which is a hot wire filament with a current running through it that emits a beam of high energy electrons. This usually knocks off one electron from each particle forming a 1+ ion.

Question 15

Why is acceleration used in a TOF instrument?

Answer 15

The positive ions are attracted towards a negatively charged plate and accelerated towards it. Lighter ions are more highly charged and reach a higher speed.

Question 16

What is ion drift in TOF?

Answer 16

When ions pass through a hole in the negatively charged plate and travel along the flight tube to a detector.

Question 17

How are ions detected in a TOF instrument?

Answer 17

Ions with the same charge arrive at the detector, lighter ions are first as they have a higher velocity. Flight times recorded. The positive ions pick up an electron from the detector, which causes current to flow.

Question 18

What are mass spectrometers used for?

Answer 18

To identify the different isotopes that make up an element as each isotopes has a different mass.

Question 19

How accurate is a mass spectrometer (decimal place)?

Answer 19

Can measure to five decimal place(high resolution mass spectrometry)

Question 20

What do the peaks in a mass spectrum graph show?

Answer 20

The relative abundance of that isotope

Question 21

What is the variable on the x-axis of a mass spectrum graph?

Answer 21

mass/charge ratio m/z

Question 22

What are the three rules for allocating electrons to atomic orbitals?

Answer 22

1) Atomic orbitals of lower levels are filled first (lower main level filled first and within this level, sub-levels of lower levels are filled first.
2) Atomic orbitals of the same energy fill singly before pairing starts (electrons repel each other).
3) No atomic orbital can hold more than two electrons.

Question 23

Which letters describe the sub levels?

Answer 23

s,p,d,f

Question 24

Which orbital is found in the first energy level?

Answer 24

single s-orbital

Question 25

Which orbital is found in the second energy level?

Answer 25

single s-orbital and 3 p-orbitals

Question 26

Which orbital is found in the third energy level?

Answer 26

single s-orbital, 3 p-orbitals & 5 d-orbitals

Question 27

How many electrons can a single atomic orbital hold?

Answer 27

2 electrons

Question 28

Define ionisation energy

Answer 28

The amount of energy it takes to remove one mole of electrons from one mole of atoms in gaseous state.

Question 29

What is ionisation energy measured in?

Answer 29

KJ mol-1

Question 30

How does the ionisation energy change for each electron removed?

Answer 30

Increases as positive ions are formed which creates a strong electrostatic attraction between the remaining electrons and the nucleus.

Question 31

How does the ionisation energy change across a period?

Answer 31

Increases as the nuclear charge increases.

Question 32

How does the ionisation energy change down a group?

Answer 32

Decreases as there are more outer shells so a greater distance between the electrons in the outer shell and the nucleus and more shielding.