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Atomic Structure I - Coggle Diagram
Atomic Structure I
The atom
History of the atom
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J J Thompson discovered electrons, which lead to the plum pudding model. Ball of + charge scattered with - electrons
Rutherford conducted the gold foil experiment and discovered that most of the atom is empty space apart from the large positive nucleus
Bohr adapted this to say that electrons orbited the nucleus in fixed energy levels, otherwsie electrons would be attracted and the atoms would collapse
Structure of the atom
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Atoms have the same number of protons and electrons, so the charge balances out and the atom has no overall charge
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Isotopes
Atoms of the same element with the same numer of protons and electrons but a different number of neutrons
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Ions
If some electrons are added or removed, the atom becomes a charged particle called an ion
When electrons leave the atom, it has positive charge
When electrons are gained, it has a negative charge
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Gold foil experimemt
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Some alpha particle were slightly deflected, so nucleus must be positively charged
Few particle were deflected by large amounts, so most of the mass is concentrated in the nucleus
Radioactivity
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Alpha decay
Consists of alpha particles, 2 protons and 2 neutrons
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Not very penetrating, stopped by a human hand
Stong ionising effect, make atoms loose electrons, creating ions
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Nuclear mass reduces by 4, positive charge reduces by 2
Beta decay
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Penetrate air and paper, stopped by aluminium
No change in mass, positive charged increase by 1
Gamma Decay
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Weak ionising, pass through rather than collide
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Activity and Half life
Activity
Radioactivity is measured with a Geiger-Muller Tube, shows the number of alpha or beta particles or gamma rays detected
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Half life is used to find the rate at which a source decays, its activity
Measured in becquerels, 1 Bq is 1 decay per second
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Overtime activity decreases because there are fewer unstable nuclei left to decay, as unstable nucleu everntually turn into stable nuclei
Half life
The time taken for the amount of radaition emitted to halve, half of the unstable atoms to decay
Each time a radioactive nuceli decays to become stable, it activity as a whole will decrease
A short half life means the nuclei are very unstable, they can be dangerous because of the high amountof radiation, but they quickly become safe
A Long half life means that the nuclei don't decay for a long time, this can be dangerous because nearby areas are exposed to radiation for a long time
We cannot predict when a particular nucleus decay, as it is random, but when there are large numbers of nuclei, hte half-life gives a good prediction of the proportion of nucleus that will decay in a given time
Short half life
Less of a risk, doesn't remain strongly radioactive
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Smoke alarms
Alpha particle emitted, and normally will reach the detector if there isn't smoke
If there is smoke, the particle won't reach as it is weakly penetrating
Amount of alpha particle detected suddenly drops, and the alarm sounds
Element used has a long half life, so doen't need to be replaced, and has a weak activity, so isn't harmful