Atomic theory 4 Flashcards
Who discovered two new elements from impure uranium salt?
Marie and Pierre Curie
Which new elements did Marie and Pierre Curie discover?
Polonium (Po) and radium (Ra)
What did Marie and Pierre discover Po and Ra from?
From impure uranium salt called pitchblende.
What did Marie and Pierre Curie notice?
That the radiation carried an electrical charge.
Who noticed that while experimenting with uranium that it was giving off some type of radiation?
Henri Becquerel
Henri Becquerel’s timeline
1852-1908
What did Henri Becquerel notice while experimenting with uranium?
He left some uranium on a photographic plate covered with black paper, the area of the photographic plate near the uranium became darker despite the fact that it had not been exposed to any sunlight = some soft of radiation.
Name an instrument that can detect radioactivity.
A Geiger-Muller tube
What does a Geiger-Muller tube do?
Detects radioactivity
What are the SI units of radioactivity?
Becquerel (Bq)
Define radioactivity
Is the spontaneous disintegration of the nucleus with the emission of α, β or γ radiation.
What is the charge on alpha particles?
Positive particles
Structure of alpha particles.
Consist of two protons and two neutrons (hence same as helium nucleus)
Penetrability of alpha particles.
- Not very penetrating
- Stopped by a sheet of papar / 5cm of air
- Strongly ionising
Are alpha particles harmless or dangerous?
Very dangerous
When are alpha particles very dangerous?
If they enter the body through the nose or mouth
What can alpha particles cause if entered through nose or mouth?
Mutations in cells
Give an example of alpha emitter and use.
- Americium-241
- Used in smoke detectors
What is the half life of americium-241?
Over 400 years
Alpha particles symbolised as
He
What is the mass of alpha particles?
4 a.m.u
What is done if an alpha particle is lost and you want to find the new element?
1 Subtract 2 from the atomic number (bottom number)
- Look up new atomic number in periodic table - find new symbol
- Subtract 4 from mass number (top number)
Po ⇾ …………….. + He
Rn
Charge of beta particles
Negatively charged particles
Structure of beta particles
Are high-speed electrons
Penetrability of beta particles
- Moderately penetrating
- Are more penetrating than alpha particles as they are lighter
- 5mm aluminium metal / 500cm of air
Why are beta particles more penetrating than alpha particles?
As they are lighter
Give an example of a beta emitter.
Carbon-14
What is carbon-14 used for?
To find the age of objects in ‘carbon dating’.
Mass of beta particles.
1/1840 a.m.u.
When are beta particles formed?
When there are too many neutrons in the nucleus to be stable.
What happens when beta particles form?
- A neutron changes into protons and an electron.
- The electron is ejected from the nucleus. The ejected electron = beta particle
Beta particles symbolised by
e
Main use of beta particles
To kill cancerous skin cells.
What happens if a beta particle is lost and you want to find the new element?
- Add 1 to the atomic number (bottom number).
- Look up periodic table to find the symbol for the new element.
- Leave the mass number the same (top number)
Example of beta particles.
Pb ⇾ Bi + e
e
0 - top
-1 - bottom
He
4 - top
2 - bottom
Gamma rays charge
Neutrally charged
Gamma rays structure
They are high-energy electro-magnetic radiation.
Name an example of a gamma emitter.
Cobalt-60
Gamma rays penetrability
- Extremely penetrating
- Several cm of lead
- Very dense metal
Does the loss of gamma radiation give rise to a new element?
No
Why doesn’t gamma radiation give rise to a new element?
As it I simply the loss of energy from the nucleus.
Main use of gamma radiation.
To treat cancer as they kill cancerous cells, but can also cause cancer as they can change the structure of our cells.
Alpha (table)
- Positive
- 2 p + 2n
- Not very penetrating
- Am-241
Beta (table)
- Negative
- Electron
- Moderately penetrating
- C-14
Gamma (table)
- Neutral
- Electromagnetic radiation
- Extremely penetrating
- Co-60
Difference between nuclear reactions and chemical reactions.
A nuclear reaction involves a change in the nucleus of an atom and a new element is usually formed as a result.
A chemical reaction involves electrons being shared or transferred from one atom to another - the nucleus of the atom remains the same.
Define chemical reaction
A chemical reaction involves electrons being shared or transferred from one atom to another - the nucleus of the atom remains the same.
Define half-life
This is the time taken / for half the nuclei / in given sized sample to decay.
Is the emission of radiation affected by external conditions like chemical reactions, pressure and temperature?
No
What is the one factor that appears to govern the overall rate of decay?
The number of nuclei left undecayed.
What is the one factor that appears to govern the overall rate of decay?
The number of nuclei left undecayed.
What do experiments show?
That the time taken for half of the atoms in a sample of a radioisotopes to decay is constant for that particular isotope.
What is the half life of radon-222?
3.2 days
What is the half life of iodine 131?
8 days
What is the half life of uranium-238?
4.5 billion years
Define radioisotopes
This is an isotope of an element that undergoes radioactive decay.
Uses of radioisotopes
- Nuclear power
- Cancer treatment
- Sterilisation
- Archaeological uses
What is meant by using radioisotopes for nuclear power?
Heat generated in nuclear power stations by nuclear reactions is used to produce electricity.
What is meant by using radioisotopes in cancer treatment?
Gamma rays of cobalt-60 are used to kill cancerous cells inside the body. Beta rays are used to treat skin cancers, as they are less penetrating.
What is meant by using radioisotopes in sterilisation?
Radiation is used to sterilise medical equipment. It is also used to kill bacteria to give food a longer shelf life.
What is meant by using radioisotopes for archaeological uses? (just understand)
The carbon-14 isotope is radioactive and is present as a very small amount of CO₂ in the air that is used by plants in photosynthesis and ends up in animals when they eat plants. The ratio of carbon-12 to carbon-14 remains constant when the organism is alive.
How can the time of death of the organism can be calculated.
By measuring the ratio of carbon-12 to carbon-14 and knowing the half-life of carbon-14.
What is nuclear fission?
A nuclear reaction in which a heavy nucleus splits spontaneously or on impact with another particle, with the release of energy.
What is nuclear fusion?
Is the joining of two smaller nuclei to form a larger one. Energy is given out.
Define radioactivity (L.C)
The spontaneous disintegration of the nucleus with the emission of α, β or γ radiation.
What change takes place in the structure of the nucleus of an atom when beta decay occurs? (L.C)
A neutron changes into a proton.
Write a balanced equation for the beta decay of a carbon-14 nucleus. (L.C)
n
A piece of fossilised yew, from a tree that was alive about 6000 years ago, was excavated from Boora Bog, Co. Offaly. When a tiny fragment of it was analysed, it was found to contain 1.5 x 10(12) carbon-14 atoms. Explain why the fragment of yew must have contained 3.0 x 10(12) carbon-14 atoms 5730 years before the analysis. What mass of carbon-14 did the fragment contain 5730 years before the analysis? (L.C)
nn
Explain why the fragment of yew must have contained 3.0 x 10(12) carbon-14 atoms 5730 years before the analysis. What mass of carbon-14 did the fragment contain 5730 years before the analysis? (L.C)
n
What are isotopes? (L.C)
Isotopes are atoms of the same element that have the same atomic number but different mass numbers due to the different numbers of neutrons present in the nucleus.
What is a radioisotope? (L.C)
n
Define the half-life of a radioisotope. (L.C)
nn
Complete the following nuclear equation to show the alpha decay of radium-226. Ra ⇾ ___ + ___ (L.C)
n
Radium-223 undergoes alpha decay and is also used in radiotherapy. Starting with a sample containing 1.0 x 10(-4) moles of radium-223, how many of these atoms remain when 87.5% of the sample has decayed? (L.C)
n
What change takes place in the nucleus of an atom when beta decay occur? (L.C)
n
Write a balanced nuclear equation for the beta-decay of the Fr nucleus (223 - top, 87 - bottom) (L.C)
n
Define radioactivity (L.C)
The spontaneous disintegration of the nucleus with the emission of α, β or γ radiation.
Give two differences between chemical reactions and nuclear reactions. (L.C)
nn
Give two properties of beta-particles. (L.C)
- Negative
- Moderately ionising
- Less penetrating power than α
A certain mass of caesium-137 leaked on a particular day. What fraction of this mass remained as caesium-137 after 90 days? (L.C)
n
What are isotopes? (L.C)
Isotopes are atoms of the same element that have the same atomic number but different mass numbers due to the different numbers of neutrons present in the nucleus.
Define radioactivity. (L.C)
The spontaneous disintegration of the nucleus with the emission of α, β or γ radiation.
Define radioisotope. (L.C)
n
Carbon-14 decays by the beta particle emission. Write a balanced equation to describe beta-decay of the carbon-14 nucleus. (L.C)
n
Explain why the carbon-12 to carbon-14 isotope ratio in the shoe leather changed over 5500 years since the shoe was made. (L.C)
nn
Define radioactivity (L.C)
The spontaneous disintegration of the nucleus with the emission of α, β or γ radiation.
Define the half-life of a radioactive isotope. (L.C)
n
Alpha particles are hazardous to human health. State one risk associated with exposure to alpha radiation. (L.C)
n
Explain why the occupants of a house fitted with smoke detectors containing americium-241 are not at risk from alpha radiation emitted by these devices. (L.C)
n
Householders are advised to replace the batteries in smoke detectors regularly. Explain whether or not the americium-241 needs to be replaced regularly also. (L.C)
n
What change occurs in the nucleus of an atom when it undergoes beta emission. (L.C)
- Neutron changes to proton
Give two properties of alpha particles. (L.C)
- Positive charge
- Poor penetration
- Stopped by a few sheets of paper
Give two differences between a nuclear reaction and a chemical reaction. (L.C)
- Involves nucleus of atoms not electron cloud
- Involves new elements being generated
Define radioactivity. (L.C)
The spontaneous disintegration of the nucleus with the emission of α, β or γ radiation.
State three properties of beta particles. (L.C)
- Negative
- Moderately ionising
- Less penetrating power than α
Explain how the carbon-14 isotope allows certain archaeological discoveries to be dated. (L.C)
- In living things, the ratio of carbon-12 to carbon-14 is constant.
- Decrease in carbon-14 related to time passed since death.
List the following three types of radiation in order of increasing penetrating power. Alpha, beta, gamma (L.C)
Alpha, beta, gamma
Explain how Rutherford interpreted the results of his experiment to conclude that the atom has a nucleus. (L.C)
- Mass concentrated / atoms mainly made up of empty space.
What are alpha particles? (L.C)
Two protons and two neutrons
Describe an experiment carried out by Rutherford and his co-workers that led to the discovery of the nucleus. (L.C)
- Bombarded gold foil with alpha particles
- Used zinc sulfide detector
- Most passed straight through
- Some were deflected at large angles
- Some were reflected
