atoms & radiation (p1) Flashcards
How much smaller is the atomic nucleus, compared to the whole atom?
10 000 times smaller
What is the basic structure of an atom?
a positively charged nucleus composed of both protons and neutrons surrounded by negatively charged electrons
What happens when electrons gain energy by absorbing electromagnetic radiation?
They move to a higher energy level (further from the nucleus).
What happens when electrons lose energy by releasing electromagnetic radiation?
They move to a lower energy level (closer to the nucleus).
How are the number of protons and electrons related in an atom?
same number of protons and electrons
How do atoms turn into positive ions?
by losing one or more electrons
What is the atomic number of an atom?
the number of protons in an atom
What is the mass number of an atom?
the total number of protons and neutrons in an atom
What are isotopes?
atoms which have the same number of protons but a different number of neutrons
ππ²π³πΌπΏπ² the discovery of electrons, what was the model of the atom?
Atoms were tiny spheres that could not be divided. Each element was made of a different type of sphere.
ππ³ππ²πΏ the discovery of electrons, what was the model of the atom?
Plum pudding model: atoms are balls of positive charge, with negative electrons embedded in it
What is the nuclear model of the atom?
The atom has a nucleus which contains most of the mass and is charged
What was Bohrβs contribution to the model of the atom?
Electrons orbit the nucleus at specific distances (called energy levels). His theoretical calculations agreed with experimental observations
What was Chadwickβs contribution to the model of the atom?
He provided the evidence to show the existence of neutrons in the nucleus. This was about 20 years after the nucleus became an accepted scientific idea
Who calculated that electrons had fixed orbits?
Bohr
Who provided the evidence to show neutrons existed?
Chadwick
After the scattering experiment, how did ideas about the nucleus develop?
Experiments showed that the nucleusβ positive charge was actually carried by more than one particle, which were named protons
How was the alpha scattering experiment conducted?
Scientists fired a beam of alpha particles at a thin sheet of gold foil and recorded where the alpha particles went
What were the results of the alpha scattering experiment?
The majority of the alpha particles went straight through the gold sheet, and some were deflected and a small number were deflected right back the way they came. The plum pudding model couldnβt explain these observations.
In the alpha scattering experiment, a few alpha particles were deflected right back and some were deflected more than expected. What did the scientists deduce from this?
This showed that most of the atomβs mass was concentrated in a central nucleus, and that the nucleus must be charged
In the alpha scattering experiment, most of the alpha particles passed straight through. What did the scientists deduce from this?
This showed that most of the atom is just empty space, rather than a solid sphere, and that the nucleus is very small relative to the size of the atom
What changes were made to the atomic model based on evidence from the alpha scattering experiment?
Most of the atomβs mass was in a central nucleus, which is charged
Most of the atom is just empty space, and that the nucleus is very small
What happens when new experimental evidence canβt be explained by an existing scientific model?
The scientific model may be changed or replaced
What do unstable isotopes tend to do?
They give out radiation from the nucleus as it changes to become more stable. This process is called radioactive decay.
What is radioactive decay?
The nucleus gives out radiation as it changes to become more stable.
What types of radiation can unstable nuclei release?
Alpha, beta, gamma, neutrons
What is alpha radiation?
two neutrons and two protons; it is the same as a helium nucleus
What is the symbol for alpha?
Ξ±
What is the mass and charge of alpha particles?
Relative mass: large.
Charge: +2
What is the ionising power of alpha radiation?
high
What is the range of alpha particles in air?
Low; a few centimetres
What materials stop alpha radiation?
Paper or skin (and anything thicker or denser than these materials)
What is the symbol for beta?
Ξ²
What is beta radiation?
a high speed electron ejected from the nucleus as a neutron turns into a proton
What is the mass and charge of beta particles?
Relative mass: very small.
Charge: -1
What is the ionising power of beta radiation?
Moderate
What is the range of beta radiation in air?
several metres
What materials stop beta radiation?
Thin sheet of aluminium (and anything thicker or denser than this)
What is gamma radiation?
electromagnetic radiation from the nucleu
What is the symbol for gamma?
Ξ³
What is the mass and charge of gamma rays?
Relative mass: 0.
Charge: 0
What is the range of gamma radiation in air?
Very high: it is not stopped by air
What is the ionising power of gamma radiation?
low
What materials reduce gamma radiation?
Several centimetres of lead or several metres of concrete. Gamma is not stopped completely.
What is a use of alpha radiation sources?
Smoke alarms
What is a use of beta radiation sources?
Testing the thickness of sheets of metal
How are beta and gamma sources used as medical tracers?
A radioactive source is injected or swallowed, and the beta or gamma emitted is followed by a detector
How can radiation be measured?
With a Geiger-Muller tube and counter, which records the count-rate.
What is the activity of a radioactive source?
how many decays happen per second
What is the half-life of a radioactive isotope?
the time it takes for the number of nuclei of the isotope in a sample to halve,
or the time it takes for the count rate (or activity) from a sample containing the isotope to fall to half its initial level
What is contamination?
The presence of radioactive ππΌππΏπ°π²π in/on an object.
What is irradiation?
Exposure to radiation.
What precautions are used to prevent irradiation?
1) Keeping sources in lead-lined boxes.
2) Staying behind barriers/in a different room
What precautions are used to prevent contamination?
1) Gloves
2) Tongs
3) Protective suits
What is ionisation?
When atoms gain or lose electrons; when ionising radiation causes the ionisation atoms πΉπΌππ² electrons
What can ionisation of living cells lead to?
Mutations (which can cause cancer) or cell death
Which type of radiation is the most ionising?
alpha
What is peer review?
when research is evaluated by other scientists (who are experts in that area of science) before it is published
Why is it important that findings of studies into radiation are published?
so that people have enough information about the risks and benefits to make informed choices
