Atomic structure

Created by

Amelie Viney

Cards (39)

How can an atom’s electron arrangement be changed?
By absorbing electromagnetic radiation
By Emitting electromagnetic radiation
Explain how an atom’s electron arrangement changed when it absorbs EM radiation:
Electrons move further away from the nucleus
They move to a higher energy level
Explain how an atom’s electron arrangement changes when it emits EM radiation:
Electrons move closer to the nucleus
They move to a lower energy level
How did the plum pudding model describe the atom?
A ball of positive charge with negatively charged electrons distributed evenly throughout it
Which experiment led to the plum pudding model being discarded?
The 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 is positively charged
What did James Chadwick’s experiments 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, their stability increases
What is count rate?
The number of radioactive decays per second for a radioactive source
Give an example of a detector that may be used to measure count rate:
Geiger-Muller tube
What are the constituents of an alpha particle?
Two protons and two neutrons
It is the same as a helium nucleus
What stops alpha radiation?
Paper
Skin
What stops beta radiation?
A thin sheet of aluminium
Several metres of air
What stops gamma radiation?
Lead
Concrete
What type of radiation is the most ionising?
Alpha radiation
What type of radiation is the most penetrating?
Gamma radiation
What changes to mass of charge occur due to emission of a gamma ray?
Both mass and charge remain unchanged
Describe the nature of radioactive decay:
Random
Impossible to predict which 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 halve
What is radioactive contamination? 
The presence of unwanted radioactive nuclei on other materials
What is irradiation? 
> The process of exposing a material to nuclear radiation
> The material does not become radioactive
Give 4 sources of background radiation:
Rocks
Cosmic rays from space
Nuclear weapon testing
Nuclear accidents
What factor determines how dangerous a particular radioactive isotope is?
The half-life
Why are isotopes with long half lives particularly harmful?
> They remain radioactive for 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
State 2 uses of nuclear radiation in the field of medicine:
Examining internal organs
Controlling and destroying unwanted tissue
How is radiation used in sterilisation?
Gamma emitters are used to kill bacteria on equipment
Explain the process of radiotherapy:
Gamma emitters direct gamma rays at cancerous cells
The cancerous cells absorb the radiation and are killed
How are medical tracers chosen?
> They should have a short half life and decay into a stable isotope which can be excreted
> They should only release gamma radiation since it is weakly ionising and can easily pass though body tissue without damaging it
What is nuclear fission?
The splitting of large, unstable nuclei to form smaller, more stable nuclei (+the emission of spare neutrons)
What usually needs to happen do induce fission?
The unstable nuclei must absorb a neutron
Alongside two smaller nuclei, what else is emitted in a fission reaction?
3 Neutrons
Gamma rays
Energy
What takes place during a chain reaction in a nuclear reactor?
> An unstable nucleus absorbs a neutron
The nucleus undergoes fission (splits into two smaller nuclei) and releases 3 further neutrons
> These induce more fission which results in a chain reaction
What are the 3 main components of the core of a nuclear reactor?
Fuel rods
Control rods
Moderator
What is the role of the moderator in a nuclear reactor?
To slow down the neutrons so they are travelling at speeds which allow them to be absorbed and cause fission
How is the fission reaction in a fission reactor kept under control?
> Control rods are positioned in between the fuel rods
> The rate of fission is controlled by moving these rods
> The lower the rods are inserted, the slower the rate of fission
What is nuclear fusion?
> The joining of two lighter nuclei to produce a heavier nuclei and release energy
> Occurs in stars
Name two isotopes of hydrogen which are commonly used in nuclear fusion:
Deuterium and Tritium
Which releases more energy, nuclear fission or nuclear fusion?
Nuclear fusion