Chemistry paper 1

• Atom


  The smallest part of an element that can exist on its own
• Types of substances


  • Element
  • Compound
  • Mixture
• Element


  • Contains only one type of atom
• Compound


  • Contains atoms of two or more elements
  • Can only be separated into their component elements through chemical reactions like electrolysis
• Mixture


  • Consists of two or more elements or compounds which aren't chemically combined
  • Components retain their properties
• Separating mixtures


  1. Physical processes which don't involve chemical reaction, so no new substances are made

  2. Filtration to separate liquids from insoluble solids

  3. Evaporation to obtain solvent from a solution
• Filtration


  • Separating sand and salt by dissolving in water and then filtering the mixture
• Evaporation


  • Obtaining salt crystals from salt water by evaporating the water
• Simple Distillation is used to obtain solvent from a solution
• Crystalisation Method

  1. React sulfuric acid with excess copper oxide

  2. Remove the excess copper oxide

  3. Heat the solution to start evaporation

  4. Turn off the heat and leave until all the water has evaporated

  5. Left with copper sulfate crystals
• Filtration


  1. Filter paper placed in a funnel over a conical flask

  2. Insoluble product left on the filter paper
• Evaporation


  1. Place mixture in an evaporating dish

  2. Slowly heat solution, solvent evaporates and the solution becomes more concentrated

  3. Keep heating the evaporating dish until you have dry crystals
• Crystallisation


  Separates a soluble solid from solutions
• Crystallisation


  1. Pour solution into an evaporating dish and heat gently

  2. When crystals start to form, remove the dish from the heat and leave to cool

  3. Crystals will come out of the solution and can be left in a warm place to dry
• Transition metals


  • In the centre of the periodic table between group 2 and group 3
  • Form coloured compounds and have ions with different charges
  • Can be used as catalysts to speed up chemical reactions
  • Good conductors of heat and electricity and are easily bent or hammered into shape
• Almost all the mass of an atom is in the nucleus
• Atoms have no overall charge as they have an equal number of protons and electrons
• Atomic number


  The number of protons in the nucleus of an atom
• Mass number


  The sum of the number of protons and neutrons in the nucleus of an atom
• Isotopes


  Atoms of the same element with the same number of protons but different numbers of neutrons
• Ions


  Atoms that have gained or lost electrons and become charged
• Group 1 - Alkali metals


  • Have one electron in the outer shell
  • Have low melting and boiling points that decrease down the group
  • Become more reactive down the group as the outer electron is further from the nucleus
  • Stored in oil to prevent reaction with oxygen and water
  • Less dense than water so can float on it
  • Produce alkaline solutions when dissolved in water
  • React with non-metals to form ionic compounds
• Group 7 - Halogens


  • Have seven electrons in the outer shell
  • Form molecules made of pairs of atoms
  • Reactivity decreases down the group as it becomes less easy to gain an electron
  • Have higher melting and boiling points further down the group
  • Form ionic salts with metals
• Electron configuration


  Electrons occupy the lowest available energy levels or shells around the nucleus
• Group 0 - Noble gases

  • Have a full outer shell of electrons so are very stable and unreactive
  • Boiling points increase down the group
• Early atom models


  Tiny spheres that could not be divided into simpler particles
• Thomson discovered electrons


  1898
• Thomson's atom model


  Contained tiny negative electrons surrounded by a sea of positive charge (plum pudding model)
• Geiger and Marsden experiment

  1. Bombarded a thin sheet of gold with alpha particles

  2. Most alpha particles flew through the sheet

  3. A tiny number was deflected
• Rutherford's nuclear model


  Positive charge in an atom must be concentrated in a very small area, named the nucleus
• Bohr's model


  Electrons orbit the nucleus at specific distances
• Chadwick provided evidence of neutrons within the nucleus
• Later experiments concluded that the positive charge could be subdivided into a whole number of smaller particles called protons