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Physics - Radioactivity and Particles - Pages 1 -10. Section 6 (Atomic…
Physics - Radioactivity and Particles - Pages 1 -10. Section 6
Atomic structure
This means that the overall charge of an atom is zero
An atom will always have the same number of electrons as protons.
An atom consists of a small central nucleus composed of protons and neutrons surrounded by electrons.
Atomic and mass number
The mass number (or nucleon number) of an atom is equal to the number of protons in its nucleus.
The atomic number (or proton number) of an atom is equal to the number of protons in its nucleus.
Properties of protons, neutrons and electrons
Neutron
Positioned in the nucleus
Relative Mass = 1
Relative electric charge = 0
Electron
Positioned outside the nucleus.
Relative mass = 0.0005
Relative electric charge = -1
Proton
They are positioned in the nucleus
Relative Mass = 1
Relative electric charge = 1
Nuclear notation
An isotope of carbon consists of 6 protons and 8 nuetrons
.
This can be written as Carbon 14 (Number of protons plus neutrons, Mass number)
Or 14 C 6
The atoms of an element always have the same number of protons.
Isotopes are atoms of the same element with different numbers of neutrons.
Ionisation
When an atom gains electrons it becomes a negative ion.
The nuclei of some isotope are unstable and when they decay they give of radiation that causes ionisation.
When an atom loses electrons it becomes a positive ion.
Ionisation occurs when an atom loses or gains one or more electrons.
Alpha,beta and gamma radiation
Alpha particle
An alpha particle consists of two protons and two neutrons.
It is strongly ionising
Gamma rays
Gamma rays are very high frequency electromagnetic waves.
They are produced when an unstable nucleus loses energy.
They are weakly ionising.
Beta particle
A beta particle is a high speed electron.
It is produced (in the nucleus) when a neutron decays into an electron and proton.
It is moderately ionising.
The penetrting power of alpha, beta and gamma radiation
1 cm of air of aluminium stops beta particles.
several cm of lead or 1m of concrete is needed to stop gamma rays.
Paper or a few cm of air stops alpha particles.
