1.2: Atomic Structure

Question 1

What does Atomic Number (Z) represent?

Answer 1

The number of protons in the nucleus of an atom

Question 2

What does Mass Number (A) represent?
Synonym?

Answer 2

The sum of protons and neutrons in the nucleus

(Also called nucleon number)

Question 3

What do the outermost electrons determine?

Answer 3

• The properties of the atom
• Reactivity - the ability to form bonds

Question 4

Define Isotopes

Answer 4

Atoms with the same number of protons but different number of neutrons

Same Atomic Number but different mass number

Question 5

What are the 3 properties of isotopes?

Answer 5

• Same outer electrons
• Same chemical identity
• Physical properties can differ

Question 6

What are the 3 isotopes of Hydrogen?

Answer 6

1. Protium - 0 neutrons
2. Deuterium - 1 neutron
3. Tritium - 2 neutrons

Question 7

What does mass spectrophotometry measure?

Answer 7

It measures the weight of atoms or compounds by observing the mass to charge ratio (m/z) of ions

Question 8

What are the applications of mass spectrophotometry?

Answer 8

• Determining the abundance of isotopes
• Identification of small molecules and proteins

Question 9

What does the height of peak and its position show you in mass spectrophotometry?

Answer 9

• Peak height gives relative abundance
• Positions of peaks gives atomic mass

Question 10

Define ‘Relative Atomic Mass’

Answer 10

The weighted average of the individial isotpes

Question 11

Can stable isotopes change?

Answer 11

NO!
They remain unchanged indefinetly

Question 12

What are the 2 properties of unstable isotopes?
Synonym?

Answer 12

1. They spontaneously disintegrate to become a stable nuclues
2. Their disintegration results in emission if small particles and/or radiation
   - They are also called radioactive isotopes

Question 13

What can both, stable and unstable isotopes be used for in scientific research?

Answer 13

• Diagnostic tools
• Trackers

Question 14

Give one application of stable isotope

Answer 14

H. pylori breath testing

Naturally occurring Carbon:
~99% Carbon - 12
1% Carbon - 13
Traces of Carbon - 14

Question 15

What happens during radioactive decay?

Answer 15

The nucleus of an unstable radioisotope seeks energetic stability by emitting particle/radiation

• alpha
• beta
• gamma photons

Question 16

What is the half life (t ½) of a radioactive isotope?

Answer 16

The time taken for the activity (of a certain amount of the substance) to decay to half the initial value

Question 17

What happens in alpha radiation?

Answer 17

• An alpha particle is emissed
• The alpha particle = Helium nuclei
• Causes a positive charge

Question 18

What happens in gamma radition?

Answer 18

• A gamma photon is emissed
• High frequency EM radiation
• Neutral, therefore atomic mass and mass number don’t t change
• Often happens with alpha or beta decay

Question 19

Why does gamma decay often happen after Alpha and beta decay

Answer 19

Alpha and beta decay leaves nucleus in excited state - It then loses energy by gamma decay

Question 20

What happens in the two types of beta radiation?

Answer 20

Beta minus - emission of an electron
Beta plus - emission of a positron (anti-electron)

Question 21

What is the capture process?

Answer 21

Where a small particle (electron, neutron etc) collides with a nucleus and is addedto it

Question 22

What can stop alpha, beta and gamma radiation?

Answer 22

Alpha - paper
Beta - Aluminuim (foil)
Gamma - thick lead

Question 23

What are the 3 industrial uses of unstable isotopes?

Answer 23

• Energy generation.
• Gamma sterilisation - Cobolt - 60
• Imaging

Question 24

What is the domestic use for unstable isotopes?

Answer 24

Smoke detectors - 241Am (americium)

Question 25

What are the 2 medical uses of unstable isotopes?

Answer 25

• Diagnostic
• Therapeutic

Question 26

What are the musts for radioisotopes used in diagnosis?

Answer 26

• Must produce gamma rays of sufficienct energy to escape from the body
• Should have a half-life short enough for it to decay away soon after imagining

Question 27

What are the 2 common isotopes used in dignostic imaging , what are their half lives and what do they emit?

Answer 27

1. 99 Tc m - 6 hours - emits gamma and low energy beta particles
2. 18 F - 110 minutes - Positron emitter (Used in fluorodeoxyglucose (FDG) to measure cell metabolism)

Question 28

In what 3 ways are unstable isotopes used in therapy?

Answer 28

• Beams of radiation
• Implanted sources (brachytherapy)
• Biologically targeted agents

Requires selective damage to unhealthy tissue

Question 29

Natural uptake??????

Answer 29

• 131I - t1/2 8.02 days; β and  emission - thyroid* 89SrCl and 153Sm - t1/2 1.93 days; β emission - bone metastasis* 32P - t1/2 14.28 days; β emission - bone marrow
  Targeted therapy e.g. Zevalin - lymphoma

Question 30

What is the Kinetic isotope effect

Answer 30

Where heavier isotopes react slightly more slowly