Detailed (periodic table)

• Periodic table


  Elements are arranged in order of atomic (proton) number (smaller number) and so that elements with similar properties are in columns, known as groups
• Elements in the same periodic group

  Have the same amount of electrons in their outer shell, which gives them similar chemical properties
• John Newlands


  • Ordered his table in order of atomic weight
  • Realised similar properties occurred every eighth element – 'law of octaves' but broke down after calcium
• Dmitri Mendeleev


  • Ordered his table in order of atomic mass, but not always strictly – i.e. in some places he changed the order based on atomic weights
  • Left gaps for elements that he thought had not been discovered yet
• The table is called a periodic table because similar properties occur at regular intervals
• Elements with similar properties are found in the same column (groups)
• Elements with properties predicted by Mendeleev were discovered and filled the gaps
• Knowledge of isotopes made it possible to explain why the order based on atomic weights was not always correct
• When electrons, protons and neutrons were discovered in the early 20th century, elements were ordered in atomic (proton) number
• When this was done, all elements were placed in appropriate groups
• Metals


  Elements that react to form positive ions
• Non-metals


  Elements that do not form positive ions
• Group 1 - Alkali metals


  • They have characteristic properties due to the single electron in their outer shell
  • Metals in group one react vigorously with water to create an alkaline solution and hydrogen
  • They all react with oxygen to create an oxide
  • They all react with chlorine to form a white precipitate
  • The reactivity of the elements increases going down the group
• Group 0 - Noble gases

  • They have 8 electrons in their outer shell (except helium, which has 2)
  • All of them (including helium) have full outer shells
  • They are unreactive and do not easily form molecules, because they have a stable arrangement of electrons (full outer shell)
  • The boiling points of the noble gases increase with increasing relative atomic mass (going down the group)
• Group 7 - The halogens


  • Similar reactions due to their seven electrons in their outer shell
  • Non-metals and exist as molecules made of pairs of atoms (e.g. Cl2)
  • They react with metals to form ionic compounds in which the halide ion carries a -1 charge
  • They react with nonmetals to form covalent compounds, where there is a shared pair of electrons
  • As you go down the group, relative molecular mass, melting point and boiling point all increase
  • Reactivity decreases down the group because halogens react by gaining an electron (to increase their number of outer shell electrons from 7 to 8) and the number of shells of electrons increases down the group, so down the group the element attracts electrons from other atoms less, so can't react as easily
  • A more reactive halogen (one from higher up group 7) can displace a less reactive one in an aqueous solution of its salt