Atomic Structure Flashcards
What do atoms contain?
Positively charged nucleus made up of protons and neutrons, which is surrounded by negatively charged electrons
What charge do protons have?
+1
What charge do electrons have?
-1
What overall charge does an atom have?
No charge as protons and electrons are equal
When might the energy level of an electron change?
When the atom emits or absorbs electromagnetic radiation
What does absorbing electromagnetic radiation do to an atom?
Moves electrons to a higher energy level, further from the nucleus
When is electromagnetic radiation emitted?
When an electron drops to a lower energy level
What does an atom that loses one of its outer electrons become?
A poitive ion
What does an atom that gains an extra electron become?
A negative ion
What is the number of protons in an element called?
Atomic number
What is the total number protons and neutrons called?
The mass number
What are atoms of the same element with a different number of neutrons called?
Isotopes
Who discovered the electron?
J. J. Thompson
When was the electron discovered
1897
What did J. J. Thompsons discovery led to?
The plum pudding model
What is the plum pudding model?
A positively charged solid sphere with negavtive electrons embedded throughout it
What did Rutherford and Marsden do in 1905?
Bombarded thin gold foil with alpha particles
What did the alpha scattering experiment prove?
That the plum pudding model was incorrect
Why did the alpha scattering experiment prove that the plum pudding model was incorrect?
The heavy, positively charged alpha particles would have passed straight through it, but some of them were reflected back meaning they must have been repelled by the same charge the alpha particles carried
What was the conclusion of the alpha scattering experiment?
The main mass of the atom was concentrated in the central nucleus which was positively charged
The electrons surrounded the nucleus
What did Niels Bohr suggest?
That electrons orbit the nucleus at specific differences
What did Chadwick prove the existence of?
The neutron
What do some unstable atomic nuclei do?
Give out radiation to become stable
What is the activity of a radioactive source?
The rate at which it decays
What are the 3 main types of nuclear radiation?
Gamma, beta and alpha
What is the ionising power of alpha radiation?
Strong ionising power
What is the ionising power of beta radiation?
Reasonable power
What is the ionising power of gamma radiation?
Poor ionising power
What is alpha radiation absorbed by?
A few cm of air or a thin sheet of paper
What is beta radiation absorbed by?
Absorbed by a few mm of aluminium
What is gamma radiation absorbed by?
Many cm of lead or many m of concrete
What are the components of alpha radiation?
Two neutrons and two protons ejected from the nucleus
What are the hazards of alpha radiation?
Highly likely to be absorbed and cause damage if passed through living cells
What are the components of beta radiation?
A high-speed electron ejected from the nucleus as a neutron turns into a proton
What are the hazards of beta radiation?
Likely to cause damage if absorbed by living cells
Can penetrate the body to inner organs
What are the components of gamma radiation?
Electromagnetic radiation emitted from the nucleus
What are the hazards of beta radiation?
Likely to pass through living cells without being absorbed and causing ionisation
What is radioactive contamination?
THe unwanted presence of materials containing radioactive atoms or other material
What is the hazard of radioactive contamination due to?
The decay of the contaminating atoms
What is irradiation?
The process of exposing an object to nuclear radiation, it can be deliberate or accidental and does not cause the object to become radioactive
What is half-life?
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
Describe an isotope with a short half-life.
Vary unstable and emit radiation very quickly, so exposure can be very hazardous
Do not remain radioactive for long
Describe an isotope with a long half-life.
They are more stable and remain radioactive for a very long time
They emit radiation slowly, so exposure is less hazardous
How is nuclear radiation involved in medical tracers?
A radioactive isotope is ingested or injected into the body
As it travels around the body, it can be detected on the outside
How can nuclear radiation be used to treat tumours?
A tumour in the thyroid gland could be treated with radioactive iodine, which gathers in the glands and destroys nearby cells
A focussed beam of gamma rays can be used to destroy some tumours
What is important to consider when choosing an isotope for a specific job?
Half-life, activity and type of radiation
Why would a gamma source make the best tracer?
They can penetrate the body and be detected from outside
They are the least ionising
What do the levels of background radiation a person experiences depend on?
Location
Job
What is nuclear fission?
The splitting of an unstable nucleus (normally uranium or plutonium)
What must usually happen for fission to occur?
The unstable nucleus must absorb a neutron first
What happens during fission?
The nucleus splits into two nuclei of roughly equal size
Emits two or three neutrons, gamma rays and energy
What do all products of fission have?
Kinetic energy
What can the neutrons emitted in nuclear fission begin?
A chain reaction
Where is the reaction of nuclear fission controlled?
A nuclear reactor
What is the explosion of a nuclear weapon caused by?
An uncontrolled chain reaction
What can nuclear fusion be thought of as?
The opposite of nuclear fission
What happens during nuclear fusion?
Two light nuclei join together to for a heavier nucleus
Some of the mass is converted into energy and some of this energy is emitted as radiation
What does nuclear fusion require?
A high temperature and pressure
Why does nuclear fusion require high temperatures and pressure?
To overcome electrostatic forces
Bring the positive nuclei close enough together so fusion can take place
What happens when an alpha particle is emitted?
Mass number of an element is reduced by 4
Atomic number is reduced by 2
What happens when beta decay occurs?
Mass number stays the same
Atomic number increased by 1
