AQA GCSE CHEMISTRY PAPER 1

• An atom is the smallest part of an element that can exist
• Chemical symbol


  Represents atoms of an element, always starts with a capital letter and consists of one or two letters
• Atoms have a radius of about 0.1 nm (1 * 10-10 m) and the radius of their nucleus is less than 1/10,000 of that of the atom (about 1 * 10-14 m)
• Element


  A substance made up of only one type of atom
• Compound


  A substance which contains two or more different elements which are chemically combined in fixed proportions
• Compounds have different properties from the elements that made them
• Compounds can only be separated into elements by chemical reactions, not physical processes
• Writing a chemical reaction

  1. Word equation

  2. Symbol equation
• To balance a symbol equation, the same number of each type of atom must be on each side of the arrow
• Key chemical formulas to know

  • Carbon dioxide (CO2)
  • Water (H2O)
  • Oxygen (O2)
  • Hydrogen (H2)
  • Nitrogen (N2)
  • Ammonia (NH3)
  • Hydrochloric acid (HCl)
  • Sulfuric acid (H2SO4)
• Proton


  Positively charged particle found in the nucleus
• Neutron


  Neutral particle found in the nucleus
• Electron


  Negatively charged particle found in shells orbiting the nucleus
• Atoms of different elements have different numbers of protons
• Atoms of the same element have the same number of protons
• Almost all of the mass of an atom is found within the nucleus
• Isotopes


  Atoms of the same element that have the same number of protons but a different number of neutrons
• Ion


  A charged particle which forms when an atom or molecule gains or loses an electron
• Electron shells


  • First shell can hold up to 2 electrons
  • Second and third shells can hold up to 8 electrons each
• Mass number


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


  The number of protons in an atom
• Determining the number of protons, neutrons and electrons in an atom

  1. Atomic number = number of protons

  2. Mass number - atomic number = number of neutrons

  3. Number of electrons = number of protons (for a neutral atom)
• Determining the number of protons, neutrons and electrons in an ion

  1. Atomic number = number of protons

  2. Mass number - atomic number = number of neutrons

  3. Number of electrons = number of protons + or - charge of the ion
• Relative atomic mass


  The average mass of all the atoms of an element compared to 1/12 the mass of a carbon-12 atom
• Neutrons


  To work out the neutrons, subtract the number of protons from the mass number
• Electrons


  For an ion, the number of electrons is one more than the number of protons to give the overall negative charge
• Relative atomic mass


  The average mass of all the atoms of an element when compared to 1/12 of the mass of a carbon-12 atom
• The relative atomic mass of some elements on the periodic table are not whole numbers because they are averages of several different isotopes
• Calculating relative atomic mass

  Multiply the percentage abundance of each isotope by its mass

  2. Add all these together

  3. Divide by the total abundance (100%)
• Mixture


  Two or more elements or compounds which are not chemically combined
• Methods to separate mixtures

  • Filtration
  • Crystallization
  • Simple distillation
  • Fractional distillation
  • Chromatography
• Filtration


  • Separates insoluble solids and liquids
• Simple distillation


  • Separates a solvent from a solution to keep the liquid
• Fractional distillation


  • Separates two or more liquids with different boiling points
• Crystallization


  • Separates a dissolved solid solute from a solution
• Chromatography


  • Separates mixtures of coloured compounds like inks or dyes
• Development of the atomic model

  Dalton's model

  Thomson's plum pudding model

  Rutherford's nuclear model

  Electron shell model

  Discovery of protons and neutrons
• Periodic table


  Elements are arranged in order of increasing atomic number, with similar properties occurring at regular intervals
• Parts of the periodic table

  • Groups (vertical columns)

  Periods (horizontal rows)
• Elements in the same group

  • Have the same number of electrons in their outer shell