the periodic table

• elements are arranged in order of atomic number and so that elements with similar properties are in groups
• element in the same periodic group have the same amount of electrons in their outer shell, giving them similar properties
• metals= elements that react to form + ions
• non-metals = elements that do not form positive ions
• group 1 = alkali metals
• group 1 properties:

  1. low mp
  2. very soft, cut with knife
  3. low densities
  4. react vigorously with water
  5. react with oxygen to create an oxide
  6. react with chlorine to form a white precipitate
  7. increases going down the group
• group 0 - noble gases

  • 8 electrons in outer shell (except for helium with 2 ) all of them have full outer shells
  • unreactive & do not easily form molecules as they have a stable arrangement of electrons
  • bp of gases increase going down the group]
• John Newlands periodic table:

  • ordered his table in atomic weight
  • realised similar properties occured 8th – ‘law of octaves’ but broke down after calcium.
  • no Nobel gases
  • more than one element in box
• Dmitri Mendeleev:

  • order of atomic mass (not strictly - sometimes atomic weights)
  • left gaps for undiscovered elements
  • predicted properties of missing elements
  • elements were discovered due to him and fitted in the gaps
  • no nobel gases
• Alkali metals - reactions:

  
• Group 0 - noble gases

  • 8 electrons in their outer shell(except helium - 2) have full outer shells
  • unreactive, and don't easily form molecules, because of their stable arrangement of electrons
  • bp increase down the group with increasing relative atomic mass
• Group 7 - the halogens

  • similar reactions due to 7 electrons in outer shell
  • non metals & found in pairs
  • they react with metals to form ionic compounds - carrying a negative charge
  • they react with nonmetals to form covalent compounds, where there is a shared pair of electrons
  • down the group - relative molecular mass, mp and bp all increase
• group 7 - halogens:

  • reactivity decreases down the group: halogens react by gaining an electron(7 to 8). the number of shells of electrons increases down the group, so down the element attracts electrons from other atoms less, so can't react as easily
  • decrease in reactivity means that a more reactive halogen (one higher up the group) can displace a less reactive one in an aqueous solution of its salt: cl will displace br if we bubble the gas through a solution of potassium bromide.