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Atomic Structure (Structure of Atom ( Relative+Mass+and+Charge+of+Subatomi…
Atomic Structure
Structure of Atom
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Because every atom contains equal numbers of protons and electrons, the positive and negative charges cancel out
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History of the Atom
Rutherford
He propose electrons must be orbiting around the nucleus which contains very densely positively charged protons
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He said the positive charge must be concentrated at a tiny spot in the centre of the atom, otherwise the large positive particles fired at the foil could never be repelled back towards their source
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Bohr
He suggested that electrons must be orbiting the nucleus at set distances in certain fixed energy levels or shells
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Geiger and Marsden
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Geiger and Marsden fired dense positively charged particles (called Alpha particles) at the thinnest piece of gold they could make
They expected the particles to pass straight through the told atoms with their diffuse cloud of positive charge
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J.J Thomson
There was a thin slit with glass behind it and the glass glowed as it was struck by rays coming in from the negative electrode
These particles were attracted to a positive charge showing they must be negatively charged themselves
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He knew atoms had to have an overall charge so he had to balance out the negative charge from the electrons
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John Dalton
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He suggested that in chemical reactions the atoms re-arranged themselves and combined with other atoms in new ways
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James Chadwick
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Because neutrons have no charge, it was very difficult to detect them
Electronic Structure
The lowest energy level (1st shell) can hold up to 2 electrons and the next energy level (2nd shell) can hold up to 8 electrons
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The number of electrons in the outermost shell of an element's atoms determines the way in which that element reacts
Isotopes
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Sometimes extra neutrons can make the nucleus unstable causing it to be radioactive, but not all isotopes are radioactive
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Isotopes have identical chemical properties but their physical properties can differ such as density
