Atomic structure Flashcards
What is the radius of an atom?
1 × 10 to the power of -10 m.
What are the charges of protons and electrons?
Protons= +1
Electrons= -1
How is electromagnetic radiation emitted?
When an electron drops in a lower energy level.
What is a positive ion?
An atom that loses one of its outer electrons to become a positive ion.
What is a negative ion?
An atom that gains an extra electron to become a negative ion.
What is the atomic number?
The number of protons in an atom.
What is the mass number?
Total number of protons and neutrons.
What is an isotope?
An atom of the same element that has a different number of neutrons.
Who discovered the electron and when was it discovered?
Discovered by J.J Thompson in 1897.
What was the plum pudding model?
It depicts the atom as a ball of positive charge with electrons embedded in it.
What did Rutherford and Marsden do in 1905?
They bombarded thin gold foil with alpha particles.
What happened in the Rutherford and Marsden experiment?
Most particles passed straight through, some particles deflected back and some particles were deflected slightly.
What was the conclusion of the Rutherford and Marsden experiment?
The conclusion was that:
-the mass of the atom was concentrated in a central nucleus, which was positively charged
-the electrons surrounded this nucleus.
How did Niels Bohr adapt this nuclear model?
He suggested that electrons orbit the nucleus at specific distances.
What did James Chadwick find out in 1932?
He discovered the neutron.
What is the activity of a radioactive source and what is it measured in?
The activity of a radioactive source is the rate at which the atom decays. Measured in becquerels (Bq).
What are the 3 main types if nuclear radiation?
Alpha, Beta and Gamma
What is the least and most ionising radiation?
Alpha is the most ionising and gamma is the least ionising.
Alpha (a).
Components- 2 neutrons/protons. Ejected from the same nucleus.
Hazards-Highly likely to be absorbed and cause damage if passing through living cells.
Beta (β).
Components- High-speed electron. Ejected from the nucleus as the nucleus turns into a proton.
Hazards-Likely to cause damage if absorbed by living cells.
-Can penetrate the body to inner organs.
Gamma (γ).
Components-Electromagnetic radiation. Emitted from the nucleus.
Hazards-Likely to pass through living cells without being absorbed and causing ionisation.
What is the 4th type of nuclear radiation?
It is a neutron (n) that can be emitted during radioactive decay.
What is radioactive contamination?
It is the unwanted presence of materials containing radioactive atoms on other materials.
What is irradiation?
-Is the process of exposing an object to nuclear radiation
-Can be deliberate or accidental
-Does not cause the object to become radioactive.
How to protect against unwanted radiation?
- By Using sources of the lowest activity possible for the shortest amount of time possible.
- Wear appropriate protective clothing such as a lead apron.
- Not handling sources with bare hands.
What is the half-life of a radioactive isotope?
-The average time it takes for half of the nuclei to decay.
-The time it takes for the count rate, or activity, of a sample containing the isotope to fall to 50% of its original value.
The half-life of a radioactive isotope is 2 years and the initial activity is 800Bq. What will be the activity after 6 years?
2 years=1/2 count rate
4 years=1/4 count rate
6 years=1/8 count rate
final count rate=1/8 * initial activity
=1/8 * 800=100Bq
What are the features of isotopes with short half-lives?
-Are very unstable and emit radiation very quickly so exposure can be very hazardous.
-Do not remain radioactive for very long.
What are the features of isotopes with short half-lives?
-Are more stable and remain radioactive for a very long time.
-Emit radiation slowly, so exposure is less hazardous.
How is nuclear radiation used in medical tracers?
They are used to look at internal organs.
-A radioactive isotope is ingested or injected into the body.
-As it travels around the body, it can be detected on the outside.
How is nuclear radiation used to monitor kidney function?
-An isotope that will pass through the kidneys is used.
-If it builds up in one kidney and not the other, this could indicate that one of the kidneys is not working efficiently.
How can nuclear radiation be used to look for blockage/damage in the intestines?
-If there is a blockage, then radioactivity cannot be detected after the blockage.
- If the intestines are damaged, the radioactive source can be seen to pass out of the intestines into other areas of the body.
How is nuclear radiation used for the treatment of tumours?
-A tumour in the thyroid gland could be treated with radioactive iodine, which gathers in the glands and destroys nearby cells.
- A focused beam of gamma rays can be used to destroy some tumours.
Which source would be the best tracer and why?
Gamma-ray because:
-They can penetrate the body and be detected on the outside.
-They are the least ionising.
What is nuclear fission?
It is the splitting of a large unstable nucleus (normally uranium or plutonium).
How does nuclear fission occur?
It will not normally occur it self-usually, the unstable nucleus must absorb a neutron first.
What happens during nuclear fission?
The nucleus:
-Splits into two smaller nuclei of roughly equal size.
-Emits two or three neutrons, gamma rays and energy.
What happens during nuclear fusion?
During fusion:
-Two light nuclei join together to form a heavier nucleus.
-Some of the mass is converted into energy and some of this energy may be emitted as radiation.
Nuclear fusion requires very high temperatures and pressures to:
-Overcome the electrostatic repulsion.
-Bring the positive nuclei close enough together for fusion to take place.
What happens when an alpha particle is emitted?
-The mass number of the element is reduced by 4.
-The atomic number is reduced by 2.
This is because 2 protons and 2 neutrons are emitted from the nucleus.
What happens when a beta particle is emitted?
-The mass number does not change.
-The atomic number is increased by 1.
This is because a neutron turns into a proton and an electron, and the electron is emitted as the beta particle.
What happens when a gamma ray is emitted?
There is no change in mass or charge of the nucleus.
How to write a balanced decay equation?
-The mass numbers on the right-hand side must add up to the same number as those on the left.
-The atomic numbers on the right must have the same total as those on the left.
Eg 219= 215 + 4 and 86= 84 +2
