P4 - Atoms & Radiation

Question 1

How did Rutherford discover the nucleus

Answer 1

Alpha Scattering Experiment:

fired a beam of alpha particles at thin gold foil. most particles went straight through the sheet but a few were deflected back and a few of those were deflected back the way they came from.

this made scientists realise that most of the mass of an atom must be concentrated at the centre in a tiny nucleus - this created the first nuclear model

Question 2

Who discovered the plum pudding model and what was it?

Answer 2

J.J Thomson
- way to remember is that “pudding” and “thomson” have the same amount of letters

the plum pudding model meant that an atom was a ball of positive charge (dough) with negatively charged electrons (currents) mixed in with the “dough”

Question 3

Who discovered the modern model of the atom and what was it

Answer 3

Niels Bohr
it meant that electrons orbited the nucleus at fixed distances

then James Chadwick discovered some particles in the nucleus have no charge at all which he then names neutrons.

Question 4

What are the subatomic particles

Answer 4

• Protons
• ELectrons
• Neutrons

Question 5

What is the relative charge of a proton and where are they found in an atom

Answer 5

Their charge is +1
They are found in the nucleus

Question 6

What is the relative charge of a electron and where are they found in an atom

Answer 6

Their charge is -1
They are found in fixed orbits around the nucleus (shells)

Question 7

What is the relative charge of a neutron and where are they found in an atom

Answer 7

Their charge is 0
They are found in the nucleus

Question 8

What happens if electrons emit or absorb electromagnetic radiation (EM radiation)

Answer 8

• If they emit EM radiation then they drop to a lower energy level/shell that’s closer to the nucleus
• If they absorb EM radiation then they move up to a higher energy level/shell that is further away from the nucleus

Question 9

What happens to an atom if it gains one or more electrons

Answer 9

it becomes a negative ion
(because its in debt which is negative)

Question 10

What happens to an atom if it loses one or more electrons

Answer 10

it becomes a positive ion
(gets rid of the surplus (yipee))

Question 11

Why do normal atoms have no overall charge

Answer 11

because: number of electrons = number of protons

so they cancel out to be neutral

Question 12

What is the mass number (top number)

Answer 12

total number of protons and neutrons in an atom

Question 13

What is the atomic number (bottom number)

Answer 13

number of protons in an atom

Question 14

What are isotopes

Answer 14

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

Question 15

What is radioactive decay

Answer 15

when an unstable nucleus decays into another element and gives out radiation to become more stable

Question 16

What is ionising radiation

Answer 16

alpha (α), beta (β) and gamma (γ) - radiation that knocks electrons off atoms, creating positive ions

Question 17

Give the characteristics of alpha particles
e.g:
- what is consists of
- what it is absorbed by
- what its range in the air is
- its ionising power
- an example of its use

Answer 17

• consists of 2 neutrons and 2 protons
  (helium nucleus)
• it is absorbed by a sheet of paper
• its range in the air is a few centimeters
• its ionising power is strong
• an example of its use is smoke detectors

Question 18

Give the characteristics of beta particles
e.g:
- what is consists of
- what it is absorbed by
- what its range in the air is
- its ionising power
- an example of its use

Answer 18

• it consists of a fast moving electron from
  nucleus
• is it absorbed by a sheet of aluminium
• its range in the air is a few metres
• its ionising power is moderate
• an example of its use it for material
  thickness testing

Question 19

Give the characteristics of gamma particles
e.g:
- what is consists of
- what it is absorbed by
- what its range in the air is
- its ionising power
- an example of its use

Answer 19

• it consists of electromagnetic radiation
  from nucleus with a short wavelength
• it is absorbed by a thick sheet of lead
• its range in the air is longer distances
• its ionising power is weak
• an example of its use is for medical tracers

Question 20

What are the 3 primary ways of detecting radiation (+ information of how they work)

Answer 20

1. Cloud chamber
   - a container full of alcohol vapor
   - ionising radiation enters the air and leaves a trail of ionised molecules
   - the alcohol vapor condenses on the ionised air molecules showing the trail of radiation
2. Photographic film
   - a bright spot appears wherever the ionising radiation hits the film
3. Geiger counter
   - ionising radiation enters a tube of low pressure gases
   - it ionises the atoms in the gas, knocking the electrons out of the atoms
   - the gas can now conduct electricity and completes an electric circuit. current flows between both electrodes
   - the current produces a clicking noise
   the count-rate is the number of decays recorded each second

Question 21

What are the charges and masses of alpha beta and gamma

Answer 21

• alpha - charge = +2, mass = 4
• beta - charge = -1, mass = 0 (electron)
• gamma - charge = 0, mass = 0

Question 22

In Nuclear equations, what does an alpha particle do

Answer 22

mass decreases by -4 (top number)
charge decreases by -2 (bottom number)

(on the right hand side of the equation after you have minused the 4 and 2, you add a helium atom to represent the alpha particle:
4 at the top, 2 at the bottom of H)

Question 23

In Nuclear equations, what does a beta particle do

Answer 23

mass doesn’t change
charge increases by +1 (bottom number)

(on the right hand side after you had added the 1 at the bottom, you need to also add an electron by writing “e” with a 0 at the top and a -1 an the bottom of it”)

Question 24

In Nuclear equations, what does a gamma particle do

Answer 24

mass and charge stay the same

Question 25

What is half-life

Answer 25

the time taken for the number of nuclei f an isotope in a sample to halve
- you can measure half life by using a graph

Question 26

What is meant by activity

Answer 26

the rate at which a source decays, measured in becquerels (Bq)

Question 27

What is meant by count-rate

Answer 27

the number of radiation counts reaching a detector per second

Question 28

What is radioactive contamination

Answer 28

getting unwanted radioactive atoms onto or into an object

Question 29

What is irradiation

Answer 29

the exposure of an object to nuclear radiation (this doesn’t make the object radioactive)

Question 30

Why can ionising radiation be dangerous

Answer 30

• it can cause cell damage:
• it can damage cells and complex chemical structures like DNA
• the cell damage from ionising radiation can cause mutations which can lead to cancer

Question 31

What are some preventative methods of reducing the risks with ionising radiation

Answer 31

• reduced exposure
• washing hands (handling)
• store radioactive substances in lead-lined boxes and locked in steel cabinets away from people
• not eat or drink when using a radioactive source and sources should be kept at an arms length away from people, not inside pockets.
• wearing protective clothing like lead aprons if you work with radioactive sources often
• standing behind a protective screen if you work with radioactive sources often

Question 32

What is the most dangerous form of radiation inside the body

Answer 32

alpha as it is the most ionising.

Question 33

Why are beta and gamma not so harmful

Answer 33

because they penetrate easier so they pass through the body

Question 34

What do scientists do to check each other’s work, theories and findings?

Answer 34

peer review

Question 35

What is the radius of an atom

Answer 35

1 x 10^-10