Atomic Structure Flashcards
Give an approximation for the radius of an atom
1x10 -10
What are the three subatomic constituent of an atom?
Protons, neutrons, electron
Where is the most of the mass of an atom concentrated?
In the nucleus
Approximately what proportion of the total radius of an atom is the radius of the nucleus?
1/10,000
Describe the arrangement of protons, neutrons and electrons in an atom
The protons and neutrons are found in the atoms nucleus
Electrons are found in a discrete energy levels around the nucleus
What type of charge does the nucleus of an atom have and why
Positive charge, the nucleus contains protons and neutrons
Protons have a positive charge
Neutrons have no charge
Give two ways, an atom electric arrangement can be changed
Absorbing electromagnetic radiation
Emitting electromagnetic radiation
Explain how an atom is electric arrangement changes when it absorbs an EM radiation
Electrons move further away from the nucleus
Move to a higher energy level
Explain how an atoms electron arrangement changes when it emits em radiation
Electrons move closer to the nucleus
They move to a lower energy level
What do all forms of the same element have in common?
They all have the same number of protons?
What is the name given to the number of protons in an atom?
Atomic number
What is an atoms mass number?
The total number of protons and neutrons in the atom
What is an isotope of an atom?
And atom of an element that has a different number of neutrons, but the same number of protons
How do atoms turn into positive ions
They lose one or more of the outer electrons
Electrons or negatively charged to the resultant charge of the atom is positive
What may lead to a scientific model been changed or replace?
The discovery of a new experimental evidence, which doesn’t agree with existing theory
How does the plum pudding model describe the atom?
A ball a positive charge, with negatively charged electrons, distributed evenly throughout
Prior to the discovery of the electron, what was believed about the atom
The atom was believed to be indivisible
Which experiment led to the plum pudding model being discarded
Rutherford is alpha scattering experiment
What is the name given to the currently accepted model of the atom?
The bohr nuclear model
State the conclusions of the alpha scattering experiment
Most of the mass of the atom is concentrated at the centre in the nucleus, the nucleus positively charge
What did James Chadwick’s experiment on the atom prove
The existence of neutrons
Why do unstable nuclei give out radiation?
Unstable, nuclei undergo decay to become more stable
As they release radiation, the stability increases
What is the name of the process in which an unstable nucleus gives out radiation to become more stable
Radioactive decay
Define the activity of an unstable nucleus
Activity is the rate of decay of a source of unstable nuclei
What is the count rate?
The number of radioactive decay per second for a radioactive source
Give an example of a detector that may be used to measure count rate
Geiger-Müller tube
What are the consiituentsof an alpha particle?
Two. Protons and two neutrons
It is the same as a helium nucleus
Which type of radiation is most ionising?
Alpha
Which type of radiation is least ionising
Gamma
Stay any changes to a mass or charge occur due to the emissions of a gamma ray
 Both mass and charge remain unchanged
Describe the nature of radioactive decay
Random
Which nuclei decay is an when is determined only by chance
It is impossible to predict which new nuclei will decay, and when
Define the half life of a radioactive isotope
The time it takes for the number of unstable nuclei in a substance to half
The time it takes for the count rate from a sample to fall to half its initial level
What is radioactive contamination?
The presence of unwanted radioactive nuclei of the materials
What is irradiation?
The process of exposing a material to nuclear radiation
The material does not become radioactive
Give four sources of background radiation
Rocks
Cosmic rays from space
Nuclear weapon testing
Nuclear accidents
How should background radiation be dealt with in calculations?
The background count should be subtracted from any readings before calculations are attempted
What is the unit used to measure radiation dosage?
Sieverts (Sv)
How many millisievert equal to 1 sievert
1000 millisievert= 1 sievert
Why might the radiation doses that different people experience differ
Some occupations involve working with radiation
Background radiation difference with location due to things such as the locality of nuclear power station or radiation related testing
What factor determines how dangerous is a particular radioactive isotope is?
The half life of the isotope
Why are isotopes of long half life particular harmful?
They remain radioactive much longer periods of time
They must be stored in specific ways to avoid humans and the environment from being exposed to radiation for too long
Give two uses of nuclear radiation in the field of medicine
Examining of internal organs
Controlling and destroying unwonted tissue
How is radiation used in sterilisation?
Gamma emmiters are used to kill bacteria on equipment
Explain the process of radiotherapy
Gamma emmiters direct gamma rays at the cancer cells
The cancerous cells absorb radiation and are killed
How are medical traces chosen?
They should have short half life and decay into a stable isotope which can be excreted
They should only release gamma radiation since it is weekly ionising, and can easily pass through body tissue without damaging it
What is the nuclear fission?
The splitting of a large, unstable, nuclei to form a smaller, more stable nuclear.
The emissions of a spare neutron
Give an example of a fissionable isotope
Urainium 235
Give an example of a fissionable isotope
Urainium 235
What usually needs to happen to induce fission
The unstable, nuclei must absorb a neutron
Spontaneous fission is rare
Alongside two smaller nuclei, what else is emitted in a fission reaction?
Two or three neutrons
Gamma rays
Energy
What form of energy do all fission products have?
Kinetic energy
What takes place during a chain reaction in a nuclear reactor
An unstable nucleus absorbs, a neutron
The nucleus, undergoes fission and releases two or three further neutrons
These induce more fission which results in a chain reaction
What is the consequence of an uncontrolled chain reaction?
The rate of fission events become to a high in results in the production of too much energy
This can lead to nuclear explosion
What are three main components of the core a nuclear reactor
Fuel rods, control rods, moderator
What is the role of the moderator in a nuclear reactor?
To slow down the neutron, so they are travelling at speed, which allows them to be absorbed by fissile nuclei and cause fission
How is the chain reaction in a fission reactor kept under control?
Control rods are positions in between the fuel rods
The rate of fission is controlled by moving the rods up and down
The lower, the rods are inserted, to slow the rate of fission
What term is used to describe nuclei, in which fission can be induced through the absorption of slow neutrons
Fissile nuclei
What is nuclear fusion?
The joining up two light nuclei to produce a heavier, nuclei and release energy
Name two isotopes of hydrogen which are commonly used in nuclear fusion
Deuterium tritium
Which releases more energy nuclear fission and nuclear fusion
Nuclear fusion
Explain the difficulty of generating energy through nuclear fusion
Fusion requires very high temperatures, which in itself requires large quantities of energy and also requires casing which can withstand them
Explain my nuclear fusion is currently not a viable way to produce energy on Earth
With current equipment/techniques, the energy required is greater than energy produced, resulting in the net energy loss
