Atomic Structure And The Periodic Table Flashcards
What are all substances made of?
Atoms (smallest part of an element that can exist)
What is an element?
A substance that contains only one sort of atom.
How are compounds formed?
From elements by chemical reactions, chemical reactions always involve a detectable energy change.
What do compounds always contain?
Two or more elements chemically combined in fixed proportions and can be represented by formulae by using the symbols of the atoms from which they are formed.
How can compounds be separated into elements?
By chemical reactions
Total mass of products=
Total mass of reactants, no atoms lost/made
What is does mixture consist of?
Two or more elements not chemically combined. The chemical properties of each substance in the mixture are unchanged.
How can mixtures be separated?
Using physical processes such as filtration, crystallisation, simple distillation, fractional distillation and chromatography.
What is filtration?
Used to separate soluble solids from insoluble solids.
E.g. a mixture of salt (soluble) and sand (insoluble) can be separated by dissolving salt in water then filtering the mixture.
What is crystallisation?
Used to obtain a soluble solid from a solution
E.g. salt crystals can be obtained from a solution of salty water.
How can salt crystals can be obtained from a solution of salty water?
1) Gently warm the mixture
2) Water evaporates leaving crystals of pure salt
What is simple distillation?
Used to obtain solvent from solution
What is fractional distillation?
Used to separate mixtures in which the components have different boiling points.
What is chromatography?
Used to separate the different soluble, coloured components of a mixture e.g. the different colours added to a fizzy drink.
What can new experimental evidence cause a scientific model to be?
Changed/replaced
What were atoms thought to be before the discovery of the electron?
Tiny spheres that could not be divided.
What did the discovery of the electron lead to?
The plum pudding model of the atom.
What did the plum pudding model suggest?
The atom is a ball of positive change with negative electrons embedded in it.
Which experiment was carried out in 1909?
The alpha particle scattering experiment where scientists fired alpha particles at a sheet of extremely thin gold foil.
What did the scientists expect to happen to the alpha particles in the experiment?
For them to pass straight through the foil or to be slightly deflected because the positive charge of each atom was thought to be spread out through the ‘pudding’ of the atom.