Atomic Structure and Radioactivity

Question 1

how does the distance of the charged particles vary with the absorption or emission of electromagnetic radiation?

Answer 1

• when atoms absorb electromagnetic radiation, the electrons at a particular level become ‘excited’ and can be pushed up to higher energy levels/ bigger distances from the nucleus
• the emission of electromagnetic radiation would cause electrons to move closer to the nucleus, to a lower energy level

Question 2

what is an isotope?

Answer 2

forms of an element that have the same number of protons (atomic number) but different numbers of neutrons (mass number)

Question 3

what is an ion?

Answer 3

Electrically charged particle, formed when an atom or molecule gains or loses electrons

Question 4

name the 5 scientists in order who made discoveries about the atomic model and when they made these discoveries

Answer 4

1. dalton 1803
2. thomson 1897
3. rutherford 1909
4. bohr 1913
5. chadwick 1932

Question 5

what did dalton discover about the atomic model?

Answer 5

1803- all matter is made of small particles called atoms and they are tiny spheres that can not be divided

Question 6

what did thomson discover about the atomic model?

Answer 6

1897- discovered electrons and that the atom can be broken down, his plum pudding model was a ball of positive charge with negative electrons in it

Question 7

what did rutherford discover about the atomic model?

Answer 7

1909- scattering experiment: positively charged alpha particles fired at gold foil bounced back meaning that the mass of the atom was concentrated in the nucleus and that the nucleus is positively charged, lead to nuclear model (atom with ball of positive charge in center and electrons floating around it)

Question 8

what did bohr discover about the atomic model?

Answer 8

1913- electrons orbit the nucleus in shells and the nucleus contains protons

Question 9

what did chadwick discover about the atomic model?

Answer 9

1932- discovered neutrons- he bombarded beryllium atoms with alpha particles and an unknown radiation was produced and he interpreted this radiation as being composed of particles with a neutral electrical charge and the approximate mass of a proton

Question 10

what is the activity of a radioactive source?

Answer 10

the rate at which its unstable nuclei decay

Question 11

what is the activity of a radioactive source measured in and by what?

Answer 11

measured in Becquerel (Bq) by a Geiger-Muller tube

Question 12

what is the penetrating power through materials of an alpha particle?

Answer 12

and alpha particle can be absorbed by skin/ paper

Question 13

what is the range in air of an alpha particle?

Answer 13

the range in air of an alpha particle is less than 5cm

Question 14

what is the ionising power of an alpha particle?

Answer 14

alpha particles have a high ionising power

Question 15

what is the penetrating power through materials of a beta particle?

Answer 15

a beta particle can be absorbed by 3mm of aluminium foil

Question 16

what is the range in air of a beta particle?

Answer 16

the range in air of a beta particle is around 1 metre

Question 17

what is the ionising power of a beta particle?

Answer 17

a beta particle has very low ionising power

Question 18

what is the penetrating power through materials of a gamma ray?

Answer 18

a gamma ray can be absorbed by lead/ concrete

Question 19

what is the range in air of a gamma ray?

Answer 19

the range in air of a gamma ray is less than 1km

Question 20

what is the ionising power of a gamma ray?

Answer 20

gamma rays have very low ionising power

Question 21

what are the uses of gamma rays?

Answer 21

• radiotherapy- beams of gamma rays can be used to kill cancerous tumours deep inside the body
• medical tracers- injected radioactive sources that emit gamma radiation can be used as tracers to make soft tissues, such as blood vessels or the kidneys, show up through medical imaging processes- x-rays

Question 22

what is a use of alpha radiation?

Answer 22

• in smoke detectors- it ionises air particles causing a current to flow and if smoke is prsent, it binds to the ions, stopping the current and the alarm goes off

Question 23

what is a use of beta radiation?

Answer 23

• to test thickness of sheets of metal as they are not immediately absorbed by them like alpha but don’t penetrate as far as gamma so slight variations in thickness affect the amount of beta radiation that will pass through

Question 24

what is the arrangement of an alpha particle and how does it change the mass number and atomic number?

Answer 24

Alpha decay (two protons and two neutrons) changes the mass number of the element by -4 and the atomic number by -2 (-4 on top, -2 on bottom, He symbol or a symbol)

Question 25

what is the arrangement of a beta particle and how does it change the mass number and atomic number?

Answer 25

Beta decay changes the atomic number by +1 because it is an electron (0 on top, -1 on the bottom, e symbol or beta symbol)

Question 26

define half-life

Answer 26

half life is the time it takes for the number of unstable nuclei or count-rate of a radioactive isotope in a sample to halve

Question 27

how do you calculate half life?

Answer 27

depending on the question * finding how much substance is left after a certain time- work out how many half-lives are in the time given and then calculate (1/2) to the power of how many half-lives it is and then put this as a ratio of the amount of substance: what is left * finding the half-life- keep on halfing the number of Becquerels until you get to the number it says it got down to to find how many half-lifes the number drops by and then divide or times this to find one half life

Question 28

what are the hazards of contamination?

Answer 28

radioactive particles could get inside your body and is radioactive for as long as the source is on or in it but is very difficult to remove

Question 29

what is a hazard of irradiation?

Answer 29

exposing objects to beams of radiation can damage living cells but doesn't make the object radioactive

Question 30

what precautions can be taken to protect against hazards from radioactive sources?

Answer 30

* keep radioactive sources shielded in a lead-lined boxwhen not in use * wear protective clothing * avoid contact with bare skin * wear face masks to avoid breathing in materials * limit exposure time * handle radioactive materials with tongs in order to keep a safer distance from sources

Question 31

is contamination or irradiation more harmful? why?

Answer 31

contamination because it ccannot be removed easily and can get inside the body making it radioactive and causing internal harm

Question 32

what is the importance of peer-review when scientists share findings of studies into the effects of radiation on humans?

Answer 32

peer review is important to check if the study: * Valid - does it measure what it says it does, was the method designed correctly and appropriately? * Original - has anyone else already carried out similar research, and has their work been credited? Are the results new? * Significant - are the findings of the research important?

Question 33

give some examples of natural and man-made background radiation

Answer 33

* mainly radon gas in rocks in the ground (natural) * buildings (man-made) * cosmic rays from space (natural) * medical sources (man-made) * food

Question 34

what are two factors that could affect the level of radiation you are exposed to?

Answer 34

occupation and location

Question 35

what is the relationship between the instability and half-life of radioactive isotopes?

Answer 35

the longer the half-life, the more stable because it takes longer to decay

Question 36

why do the hazards associated with radioactive material differ according to the half-life involved?

Answer 36

* because if a radioactive substance has a very long half-life, we know that it will remain radioactive for a very long time * the longer a substance remains radioactive, the more dangerous it is

Question 37

describe and evaluate the uses of nuclear radiation in exploration of internal organs and controlling/ destroying unwanted tissue?

Answer 37

* exploring internal organs- medical tracers can be used to help diagnose problems but could have a small risk of damage to living cells/ tissue * controlling/ destroying unwanted tissue- radiotherapy is used to kill cancer cells but ultimately damages to some normal cells too, leaving the patient with side effects/ feeling ill

Question 38

describe nuclear fission

Answer 38

* the splitting of a large nucleus to produce two smaller ones * two or three neutrons are also released in the process which then collide with other unstable nuclei, causing them to split= a chain reaction happens * this makes nuclear energy

Question 39

describe nuclear fusion

Answer 39

* nuclear fusion is when two small, light nuclei join together to make one larger nucleus * since nucleuses are positive, they repel and are very unlikely to collide unless they are moving very fast with lots of energy * this happens in stars like the sun