a charged particle - there aren't the same number of protons and electrons
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What is an atomic number?
number of protons = number of electrons
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What is a mass number?
number of protons + neutrons
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What are elements?
atoms with the same atomic number
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What are isotopes?
an element with the same number of protons but a different number of neutrons (same atomic number, different mass number)
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What is a compound?
two or more elements chemically combined - bonds difficult to separate
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What is a mixture?
two or more substances that are not chemically combined - easy to separate
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Filtration
separates solids from liquids
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Evaporation
separates a soluble salt from a solution (fast)
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Crystallisation
separates a soluble salt from a solution (slow)
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Separating salt from rock salt
1. grind the mixture of salt, 2. add water and stir, 3. filter the mixture - leave sand in filter paper, 4. evaporate water from salt - leaving crystals
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Simple distillation
separates a liquid from a solution - heat solution until evaporation of liquid, goes through condenser, condenses back into a liquid, collected in a beaker
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Fractional distillation
separates a mixture of liquids - same as simple distillation but uses a fractionating column filled with glass beads, liquids with different boiling points
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Paper chromatography
separates mixtures of substances (with different solubilities) dissolved in a solvent as they move up a piece of chromatography paper
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John Dalton - c19th
described atom as a solid sphere
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J.J. Thomson - 1897
plum pudding model - atom is a ball of charge with scattered electrons
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Ernest Rutherford - 1909
nuclear model - alpha particles through gold foil - most particles passed through - some were deflected off course - dense region of positive charge at centre of atom (nucleus) that repelled alpha particles -
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