Atomic Structure Flashcards
What are the relative charges and masses of the three subatomic particles?
Protons have a relative mass of 1 and charge of +1
Neutrons have a relative mass of 1 and charge of 0
Electrons have a very small relative mass, practically 0, and a charge of -1
Where are the protons, neutrons and electrons found in an atom?
Protons and neutrons make up the nucleus, and electrons are in energy levels around the nucleus, or shells
What determines the identity of an element?
The atomic number (the number of protons), as each element has a different number of protons all together
What is an isotope? Give an example
Atoms of the same element with the same number of protons but a different number of neutrons
e.g. Carbon-12 and carbon-14
What was John Dalton’s model of the atom?
He proposed that atoms were small solid spheres that couldn’t be divided
Who came up with the plum pudding model and how does it describe the atom?
JJ Thomson said that the atom was a positively charged sphere with negatively charged electrons suspended in it
Who did what experiment that led to the discovery of the nucleus of the atom?
Ernest Rutherford conducted the gold foil experiment
What did Rutherford’s experiment show?
Most alpha particles that were shot at the gold foil passed through - the atom is mostly empty space
Some were deflected and changed in the angle of their direction after hitting the foil - shows that there is a small, positively charged nucleus
A few bounced back - shows that nucleus is dense and contains most of the mass
How did Neils Bohr improve Rutherford’s model of the atom?
He proposed that electrons orbit in fixed energy levels, or shells
What discovery about the atom was made by James Chadwick?
He discovered the neutron, which explains isotopes and why the nucleus is heavier that just the protons alone
What is an unstable nucleus?
A nucleus with an imbalance of protons and neutrons, leading to radioactive decay
When does radioactive decay occur?
When an unstable nucleus releases energy in the form of radiation until it becomes stable
What is radioactive decay measured by?
A Geiger-Muller tube and counter which records the count rate, or the number of radiation counts reaching it per second
What can be used to make predictions about radioactive sources?
Half-life, which is the time taken for the number of radioactive nuclei in an isotope to halve
What can be used to make predictions about radioactive sources?
Half-life, which is the time taken for the number of radioactive nuclei in an isotope to halve
Why can’t we tell exactly when a nucleus will decay?
The process is random
What are the three types of radiation?
Alpha, beta and gamma
Describe alpha decay
This is where the nucleus loses 2 protons and 2 neutrons. This causes the atomic number of the atom to decrease by 2, and the mass number by 4
Describe beta decay
This is where a neutron in the nucleus turns into a proton, and an electron (beta particle) is emitted. This causes the atomic number to increase by one with no change to the mass number
What is gamma radiation?
This is where pure energy is released as gamma rays from the nucleus, with no change in atomic or mass number
What is an alpha particle?
It the same as a helium nucleus - 2 protons and 2 neutrons - and is emitted during beta decay
What is a beta particle?
A high energy electron emitted during beta decay
Compare the properties of alpha beta and gamma radiation
What is the definition of half-life?
The amount of time taken for half the radioactive nuclei in a sample to decay
It is measured in Becquerels, which is the rate at which it decays, or it’s activity
What is ionising radiation?
Radiation that has enough energy to knock electrons out of atoms, creating ions (charged particles)
What is contamination?
It occurs when radioactive material is present on or inside an object or person
What is irradiation?
When something is exposed to radiation, but no material is left behind, so the exposure stops when the source is removed
What are the dangers of ionising radiation?
Can cause cell mutations, tissue damage and cancer
What are some ways of reducing irradiation?
Keeping sources in lead-lined boxes, standing behind barriers
What are some ways of reducing risk of contamination?
Using gloves and tongs when handling sources, using PPE to prevent inhalation of particles.
What is nuclear fission?
The splitting of a large nucleus into smaller nuclei, releasing gamma rays and neutrons, and energy is released
What is nuclear fusion?
The fusing of two small nuclei to form a larger nucleus releasing huge amounts of energy
Why is nuclear fusion difficult to achieve on earth?
The process requires incredibly high temperatures and pressure to force nuclei together
How is alpha radiation used in smoke detectors?
Alpha particles ionise air particles, which creates a small electrical current. Smoke disrupts the current, which triggers the alarm
How is alpha radiation used in medical treatments?
It is used in internal radiotherapy, as it is highly ionising with a small range, which makes it useful for destroying cancer cells without affecting too much surrounding healthy tissue
How is beta radiation used in industry?
Beta particles are used in industry to measure the thickness of different materials, by measuring how much radiation passes through the material, the thickness can be adjusted precisely
What does a short half-life mean?
It means that activity falls quickly because the nuclei are very unstable and so rapidly decay.
What does a long half-life mean?
The activity falls more slowly because most of the nuclei don’t decay for a long time
How does half-life link to the danger of radiation?
Short half-life = dangerous because of the high emission of radiation at the start, but they become safe quickly
Long half-life = dangerous because nearby areas can be exposed to radiation for years
What is background radiation?
The low-level radiation that is around us all the time
What is the background radiation that comes from space?
Cosmic rays that mostly come from the sun, but are mostly blocked by the Earth’s atmosphere
What background radiation is present from human activity?
Fallout from nuclear explosions, or nuclear waste
(Makes up a very small proportion of the total background radiation)
Outside the body, which radiation sources are the most dangerous?
Beta and gamma, as they can penetrate the skin and reach delicate organs.
Why is alpha radiation the least dangerous outside the skin?
It can’t penetrate the skin and is easily blocked by a small air gap, as they have a very small range in air
Inside the body, which type of radiation is the most dangerous?
Alpha, as they are the most ionising and do all their damage in a very localised area.
How small are atoms?
Have a radius of 1×10^10
What is the radius of a nucleus in comparison to the whole atom?
Less than 1/10 000 of the radius of the atom
How can electron arrangements change?
They can change with the absorption of electromagnetic radiation (electrons move further from the nucleus, a higher energy level)
Or by the emission of EM radiation (move closer to the nucleus, a lower energy level)
How was Niels Bohr’s theory about electrons proved correct?
His theoretical calculations agreed with scientific observations
What type of radiation is used for medical tracing and why?
Gamma sources are usually used as they can pass through the body and can be detected outside it:
- they are highly penetrating meaning detectors can monitor their movement
- they are lowly ionising meaning they are less damaging to body tissue than alpha or beta
How does radiotherapy work?
Gamma rays are targeted at cancer cells, and ionise them to kill them. However, this can also destroy normal healthy cells causing tissue damage, which can have side effects on a patient
What is a risk of using too low a dose of radiation during e.g. radiotherapy?
This may lead to not enough radiation to kill cells, but only enough to mutate their DNA, which can lead to uncontrollable division, or cancer
What may the neutrons that are products of nuclear fission start?
A chain reaction
How does a nuclear reactor work?
It is a controlled fission reaction, changing how quickly the chain reaction occurs. This is done by control rods, which when lowered and raised, absorb neutrons, slowing down the chain reaction
How do nuclear weapons work?
An uncontrolled chain reaction of nuclear fission resulting in an explosion
