topic 1

• Atom


  Smallest part of an element that can exist
• Chemical symbol


  Represents an atom of an element
• Elements


  • Substances with only one type of atom
  • Listed in the periodic table
  • About 100 different elements
• Elements


  • Can be classified as metal or non-metal
  • Columns in periodic table are called groups and contain similar elements
  • Rows in periodic table are called periods and elements show a gradual change in properties across a period
• Compound


  Made from two or more different elements (types of atoms) combined together in fixed proportions
• Compounds have different properties from the elements they are made from
• Compounds can only be separated into elements by chemical reactions
• Mixture


  Two or more elements or compounds not chemically combined together
• The chemical properties of each substance in a mixture are unchanged
• Separating Techniques


  1. Filtration

  2. Crystallisation/Evaporation

  3. Simple Distillation

  4. Fractional Distillation

  5. Chromatography
• Simple Distillation


  Separates a soluble solid and a liquid (e.g. salt and water)
• Crystallisation/Evaporation


  Separates a soluble solid from a (non-flammable) liquid
• Filtration


  Separates an insoluble solid suspended in a liquid (usually water)
• Fractional Distillation


  Separates soluble liquids with different boiling points (e.g. crude oil)
• The fractionating column has a temperature gradient and is hotter at the bottom than at the top
• The liquid with the lowest boiling point will be the first 'fraction' to collect
• Plum-pudding model


  Suggested the atom was a ball of positive charge with negative electrons embedded in it
• Nuclear model


  The centre of the atom was called the nucleus, with electrons orbiting the nucleus
• Bohr model


  Electrons orbit the nucleus at specific distances, on energy levels or shells
• The experimental work of Chadwick provided evidence for the existence of neutrons within the nucleus
• Atom


  Has a small central nucleus made up of protons and neutrons, around which there are electrons
• Subatomic particles


  • Proton
  • Neutron
  • Electron
• In an atom, the number of electrons is equal to the number of protons in the nucleus, so atoms have no overall electrical charge
• Atomic number


  The number of protons in an atom
• Mass number


  The total number of protons and neutrons in an atom
• Isotopes


  Atoms of the same element with different numbers of neutrons
• Isotopes of an element have the same chemical properties because they have the same electronic structure
• Calculating Relative Atomic Mass


  R.A.M = (isotopic mass x % abundance) / 100
• Electronic structure


  Electrons occupy particular energy levels, with the lowest available energy levels occupied first
• Elements in the same group in the periodic table have the same number of electrons in their highest energy levels (outer electrons) and this gives them similar properties
• The elements in Group 0 of the periodic table are called the noble gases, and are unreactive because their atoms have stable arrangements of electrons
• Modern Periodic Table


  • Arranged in order of atomic (proton) number
  • Elements with similar properties are in columns, known as groups
  • Can be seen as an arrangement of the elements in terms of their electronic structures
• Metals


  Elements that react to form positive ions
• Non-metals


  Elements that do not form positive ions
• Group 1: Alkali Metals


  • All have 1 electron in their highest energy level
  • Are metals with low density
  • Are stored under oil to prevent them from reacting
• In group 1, the further down the group an element is


  The more reactive it becomes
• Reaction of Group 1 metals with water

  Releases hydrogen and forms hydroxides which dissolve in water to give alkaline solutions
• Group 0: Noble Gases


  • Unreactive and do not easily form molecules
  • Have eight electrons in their outer energy level, except for helium which has two
• Group 7: Halogens


  • All have 7 electrons in their highest energy level
  • Have coloured vapours
  • Form ionic salts with metals and molecular compounds with other non-metals
• Displacement Reactions in Group 7


  A more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt