Compounds and elements

• Elements ending in -ide

  • 2 elements
• Elements ending in -ate

  • 3 elements
• Each capital letter represents an element
• Magnesium Oxide


  A compound
• Isotopes


  Chemical twins or triplets that are different forms of the same element with the same number of protons but a different number of neutrons
• Relative atomic mass of Lead is 203, 207
• Halogens exist in the following states: gas, solid, liquid
• Relative molecular mass (Mr)


  The same as working mass
• Volume units


  • 1000 cm3 = 1 dm3 (1 Litre)
  • To convert: divide cm3 by 1000 to get dm3, multiply cm3 by 1000 to get dm3
• Compounds


  Substances formed from two or more elements, with the atoms of each in fixed proportions and held together by chemical bonds
• Formation of compounds


  1. Atoms combine by giving away, taking or sharing electrons

  2. Compounds formed from a metal and a non-metal consist of ions

  3. Compounds formed from non-metals consist of molecules
• The properties of a compound are usually totally different from the properties of the original elements
• Chemical formula


  A representation of the composition of a compound using the symbols of the elements and numbers to show the relative numbers of atoms
• Chemical equation


  A representation of a chemical reaction showing the reactants and products
• Balancing chemical equations


  1. Ensure the same number of atoms of each element on both sides of the equation

  2. Adjust the coefficients in front of the formulas to balance the equation
• Atoms


  Join together to make compounds
• When elements react together

  Atoms will combine with other atoms to form compounds
• Compounds


  • Consist of two or more elements
  • Held together through chemical bonds
• Making chemical bonds


  1. Involves atoms giving away or sharing electrons

  2. Only electrons are involved, the nuclei of atoms are not involved
• Compound formed from a metal + non-metal


  Consists of ions
• Metal atoms


  Lose electrons to form positive ions
• Non-metal atoms


  Gain electrons to form negative ions
• During a chemical reaction


  At least one new substance is made
• Once the bond is formed, it is usually difficult to separate the original elements
• Properties of compounds


  • Usually very different from the properties of the original elements
  • React differently from elements
• Compounds formed from elements

  • Iron sulfate
  • Carbon dioxide
  • Sodium chloride
  • Water
  • Ammonia
  • Carbon monoxide
• Compounds formed from non-metals

  Made of molecules