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4. Atomic structure
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- 1What was the first modern theory of atoms?in the early 1800s, John Dalton agreed with Democritus that matter was made form tiny spheres, but reckoned each element was made of different types of atom.
- 2What did J.J. Thompson discover and conclude?In the early 1900s, J.J. Thompson discovered electrons that could be removed from atoms. He suggested that atoms were spheres of positive charge with negative electrons stuck in them - the plum pudding model?
- 3How was the plum pudding model disproved?In the early 1900s, Rutherford fired positive alpha particles at a sheet of gold and found some were slightly deflected or passed straight through. He concluded there was positively charged nucleus surrounded by a cloud of electrons.
- 4Who discovered electron shells?Niels Bohr said the electrons orbiting the nucleus were at certain distances called energy levels.
- 5Who discovered the neutron and when?In the 1930s, James Chadwick proved the existence of the neutron, which explained imbalances between atomic and mass numbers.
- 6What is an isotope?Isotopes are atoms with the same number or protons and electrons but a different number of neutrons.
- 7What is an unstable isotope?An unstable isotope, or radioisotope, has too many or not enough neutrons in the nucleus, resulting in radioactive decay as the nucleus rearranges itself.
- 8What can certain radioisotopes be used for?- To show up on medical imaging and x-rays as a medical tracer.
- To allow chemists to follow how a reactions work and act as marker.
- For radiotherapy. - 9What can radioactive substances emit during radiation?Alpha, beta and gamma radiation (ionising radiation) and neutrons.
- 10What are alpha particles and their properties?Alpha particles (α) are helium nuclei, with two protons and two neutrons. They don't penetrate materials easily and can be absorbed by a sheet of paper. They are strongly ionising due to their size and resultant collisions with other atoms.
- 11What are beta particles and their properties?Beta particles (β) are fast-moving electrons (e-). They penetrate materials moderately well and can be absorbed by a sheet of aluminium. They are moderately ionising. For every beta particle released, a neutron in the nucleus has turned into a proton.
- 12What are gamma rays and their properties?Gamma rays (γ) are waves of electromagnetic radiation. They penetrate materials very well and can be absorbed by thick sheets of lead or metres of concrete. They are weakly ionising because they tend to pass through rather than collide with atoms.
- 13What is the symbol for beta radiation in nuclear equations?Plus the nucleus changes a neutron to a proton.
- 14What is the symbol for alpha radiation in nuclear equations?
- 15How do gamma rays affect an atomic mass and number?Neither of them change, gamma rays are a way of getting rid of excess energy.
- 16How can radiation be measured?A Geiger-Muller tube and counter records the count-rate (radiation counts reaching it per second).
- 17What is a half-life and why is it measured?A half-life is the time taken for the number of radioactive nuclei in a sample to halve, which is measured because radiation is a random process which never reaches 0.
- 18How is the half-life of an isotope related to its instability?The more unstable a nucleus is, the faster it will decay, meaning the half-life will be shorter.
- 19What is radioactive activity measured in?Becquerels (Bq), which is average number of decays per second.
- 20Where can background radiation come from?- Air, food, building materials and rocks in the earth.
- Space, which is known as cosmic rays and are mostly from the Sun. The atmosphere protects us from most of this.
- Human activity e.g. fallout from nuclear waste. - 21What is irradiation?Irradiation is when objects near to a radioactive source are exposed to it, but this does not make it radioactive.
- 22When are alpha, beta and gamma radiation most dangerous to people?Outside the body, beta and gamma are more dangerous because they can access delicate organs. Inside the body, alpha radiation is more dangerous because it cannot get out and does damage in a localised area.
- 23How do irradiation and contamination damage the body?Radiation can enter living cells and ionise atoms and molecules within them. This can either cause tissue damage and radiation sickness with higher doses or mutant cells resulting in cancer with lower doses.
- 24What is an example of a medical tracer?Iodine-123 can be absorbed by the thyroid gland like iodine-127 normally is, but it gives out radiation which can be detected to check iodine is being absorbed.
- 25What is radiotherapy?Gamma rays are directed at just the right dosage to target cancer cells whilst doing as little damage as possible to normal cells.
- 26What type of radioactivity do medical tracers have and why?Medical tracers emit gamma radiation so it can get out of the body easily and cause as little damage as possible.
- 27What is nuclear fission?Nuclear fission is the splitting of a large, unstable nucleus to release energy. Spontaneous fission rarely happens, as a nucleus usually has to absorb a neutron to split.
- 28How can a chain reaction occur in nuclear fission?As two or three neutrons are released when an atom splits, if any of these are moving slow enough to be absorbed by another nucleus, more fission can occur.
- 29Where does the energy go from nuclear fission?Some energy is transferred to the kinetic energy stores of the neutrons and other products, the rest is carried away by gamma rays.
- 30How can the amount of energy produced from nuclear fission be controlled?Use of control rods, which are lowered and raised inside a nuclear reactor to absorb neutrons and change the rate of a chain reaction.
- 31How do nuclear weapons work?Uncontrolled chain reactions of nuclear fission quickly lead to lots of energy being released in an explosion.
- 32What is nuclear fusion?Nuclear fusion is when two light nuclei collide at high speed and fuse together to form a larger nucleus. This has a little less mass than the two lighter nuclei, as some of the mass is converted to energy.
- 33Why isn't nuclear fusion used for common energy production?Scientists haven't found a way to have the right conditions, a very high temperature and pressure, and the reactors would be very hard and expensive to build.
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- GCSE Physics Fichas sobre 4. Atomic structure, creado por JR HN el 24/10/2018.
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