C1 - Atomic Structure

• All substances are made up of atoms
• The periodic table losts all the chemical elements, with 8 main groups each containing elements with similar properties
• Elements contain only one type of atom
• Compounds contain more than one type of atom
• An atom has a tiny nucleus at its centre, surrounded by electrons
• No new atoms are ever created or destroyed in a chemical reaction


  The total mass of reactants = the total mass of products
• There is the same number of each type of atom on each side of a balanced symbol equation
• You can include state symbols to give extra information on balanced symbol equations.

  • (s) for solids
  • (l) for liquids
  • (g) for gases
  • (aq) for aqueous solutions
• A mixture is made up of 2+ substances that are not chemically combined together
• Mixtures can be seperated by physical means, such as filfiltration, crystallisation, and simple distillation
• Fractional distillation

  • Effective way of separating miscible liquids, using a fractionating column
  • Separation is possible because of the different boiling points of the liquids in the mixture
• Paper chromatography


  • Separates mixtures of substances dissolved in a solvent as they move up a piece of chromatography paper
  • Different substances are separated because of their different solubilities in the solvent used
• Bohr's model of the atom shows that electrons fall to lower energy levels when they lose energy
• Atoms


  • Made of protons, neutrons, and electrons
  • Protons have a relative charge of +1, electrons have a relative charge of -1, neutrons have no electric charge
  • Relative masses of a proton and a neutron are both 1
  • Atoms contain an equal number of protons and electrons, so carry no overall charge
  • Atomic number = number of protons (= number of electrons)
  • Mass number = number of protons + neutrons
  • Atoms of the same element have the same number of protons (and hence electrons) in their atoms
• Ions

  Atoms that gain electrons form negative ions, atoms that lose electrons form positive ions
• Isotopes


  Atoms of the same element with different numbers of neutrons, have identical chemical properties but different physical properties such as density
• Electron arrangement in atoms

  • Electrons are arranged in energy levels or shells
  • Lowest energy level (1st shell) can hold up to 2 electrons, next energy level (2nd shell) can hold up 8 electrons
  • 4th shell starts to fill after 8 electrons occupy the 3rd shell
  • Number of electrons in the outermost shell determines how an element reacts