C1

• There are 118 different elements
• Atoms are the smallest pieces of an element that can exist
• The nucleus is made up of protons and neutrons, which have almost equal masses.
• Protons carry positive charge while electrons carry negative charge.
• Atoms of different elements can be combined together to create compounds
• Compounds have formulae that are made by combining the chemical symbols of the elements that combine to make them
• Combining different atoms creates different compounds
• Key features of a chemical reaction are:

  • Compounds are broken up or formed
  • At least 1 new substance is created
  • Measurable energy change
  • No atoms are created or destroyed
• A chemical equation shows what happens in a chemical reaction using symbols or words
• Symbol equations must be balanced
• Mixtures are made of 2 or more substances (elements or compounds) that haven't been chemically combined
• Mixtures can be seperated
• Mixtures chemical properties dont change because they have been mixed with another substance
• We can normally separate mixtures and compounds into the elements or compounds that are found in them. We use physical processes to separate them. These processes don't create new chemical substances (there are no chemical reactions)
• Filtration, crystallisation, chromatography, distillation, fractional distillation are all examples of separating mixtures
• Filtration - separates mixtures of insoluble solids and liquids, done by pouring water through filter paper
• Crystallisation - separates solutions into their constituent parts, dissolved solids and liquids. Eventually, crystals of the solute will form, and we can collect the solvent by condensing it as it evaporates
• Chromatography - Separates solutions with a number of different solutes in the solvent. Done by placing a drop of solution to be separated near the bottom of a piece of chromatography paper, dipping the bottom into a suitable solvent. The solvent moves up the paper and carries the solutes with it
• Simple distillation - separates 2 liquids with different boiling points. The mixture is heated until the liquid with the lower boiling point starts to boil. The vapour released passes through a condenser, where the gas cools back into a liquid
• Fractional distillation is used to separate a mixture of liquids into two or more fractions
• Everything is made up from tiny little particles that can't be broken down any further and that they're separated from each other by empty space
• Atomic theory


  The idea that everything is made up from tiny little particles that can't be broken down any further and that they're separated from each other by empty space
• Democritus' atomic theory

  • Everything is made up from tiny little particles that can't be broken down any further
  • Particles are separated from each other by empty space
• Improvements made to atomic theory

  1800s
• John Dalton's atomic theory


  Atoms are solid spheres. Different types of spheres might make up the different elements
• J.J. Thompson proposed the plum pudding model


  1897
• J.J. Thompson's plum pudding model

  • Atoms contain negatively charged particles (electrons)
  • Atoms are not solid spheres
• Rutherford and his students made a big discovery


  1909
• Rutherford's experiment


  1. Fired positively charged alpha particles at a thin sheet of gold

  2. Some alpha particles were deflected to the side

  3. A small number were deflected back the way they had come
• Rutherford's nuclear model


  Atoms have a compact nucleus containing all the positive charge<|>Negative charge exists in a cloud around the nucleus
• Rutherford's nuclear model had a flaw - it didn't explain why the atom doesn't collapse
• Niels Bohr suggested a solution to the flaw in Rutherford's model

  1913
• Niels Bohr's model


  Electrons orbit the nucleus in shells<|>This prevents the atom from collapsing
• Further experiments supported Bohr's model with a few small changes
• Current understanding of the atom

  • Positive charge in the nucleus is made up of protons
  • Neutral particles called neutrons are also in the nucleus
• Atom


  The thing that is uncuttable, indivisible
• John Dalton theorized that atoms were spherical and of the same element were identical


  1808
• John Dalton's atomic model


  Atoms are spherical and atoms of the same element are identical in size and mass
• JJ Thomson proposed the plum pudding model of the atom


  Around 1898
• JJ Thomson's plum pudding model


  The atom is a sphere of positive charge with randomly spread out negative charges (electrons) inside