chemistry.

chemistry.

1. unit 1: atomic structure.

   • atoms
     • all substances are made up of atoms.
     • the periodic tale lists all the chemical elements, with eight main groups each containing elements with similar chemical properties.
     • elements contain only one type of atom.
     • compounds contain two or more elements.
     • an atom has a tiny nucleus at its centre, surrounded by electrons.
   • chemical equations.
     • no new atoms are ever created or destroyed during a chemical reaction: total mass of reactants = total mass of products.
     • there is the same number of atoms on each side of a balanced symbol equation.
     • add state symbols to add information to balanced symbol equations. (s) for solids, (l) for liquids, (aq) for aqueous solutions, and (g) for gases.
   • separating mixtures.
     • a mixture is made up of two or more substances that are not chemically bonded.
       • mixtures can be separated by physical means, such as filtration, distillation, and chromatography.
   • fractional distillation and paper chromatography.
     • fractional distillation is an effective way of separating miscible liquids, using a fractionating column. the 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. the different substances are separated because of their different solubilities in thee solvent used.
   • history of the atom
     • the ideas about atoms have changed over the years.
       • new evidence has been gathered from experiments of scientists who have used their model of the atom to explain their observations and calculations.
     • key ideas were proposed successfully by Dalton, Thomson, Rutherford, and Bohr, before arriving at the model used today.
   • structure of the atom.
     • atoms are made of protons, neutrons, and electrons.
       • protons have the relative charge of +1. electrons have the relative charge of -1 and neutrons carry no charge.
         • neutrons are neutral.
     • protons and neutrons both have the relative charge of 1.
       • atoms with equal numbers of protons and electrons have no overall charge.
         • atomic number = number of protons (or electrons).
           • mass number = number of protons + number of neutrons.
     • atoms of the same elements have the same number of protons and electrons in their atoms.
   • ions, atoms and isotopes.