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The atom is composed of protons, neutrons and electrons
subatomic particle relative mass relative charge
proton 1 +1
neutron 1 0
electron 1/2000 1
A nucleon is a particle of the nucleus and may be either a proton or a neutron.
The nucleon number is the number of protons plus the number of neutrons in the
The number of protons in the nucleus is the atomic number
In a neutral atom the number of protons is equal to the number of electrons.
Atoms may lose or gain electrons to form charged particles called ions.
All atoms of a particular element have the same number of protons.
Atoms of different elements have different numbers of protons.
Atoms of the same element (same number of protons) which have different numbers
of neutrons are called isotopes.
An early model scientific idea about the structure of the atom was called the
plum pudding model. In this model, the atom was imagined to be a sphere of
positive charge with negatively charged electrons dotted around inside it like plums
in a pudding.
Rutherford designed an experiment to test the plum pudding model. A beam of
alpha particles (positively charged) was aimed at very thin gold foil and their
passage through the foil detected. The scientists expected the alpha particles to pass
straight through the foil, but something else also happened.
Some of the alpha particles emerged from the foil at different angles, and some even
came straight back. The alpha particles were being repelled and deflected by a tiny
concentration of positive charge in the atom: the NUCLEUS. As a result of this
experiment, the plum pudding model was replaced by the nuclear model of the
Some insulating materials can become electrically charged when rubbed together.
This arises because electrons are transferred from one material to another.
The material that gains electrons becomes negatively charged while the material
that loses electrons becomes positively charged.
Two materials with the same charge repel each other (electrostatic force of
repulsion) while two materials with opposite charge attract each other
(electrostatic force of attraction). The strength of the force decreases as separation
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A charged conductor can be discharged by connecting it to earth with a conducting
The flow of electrons through a conductor is referred to as an electric current.
The greater the charge on an isolated object, the greater the potential difference
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