Periodic table

• Mendeleevs periodic table 


  1869

  Arranged in order of relative atomic mass

  Arranged elements in groups with eleme ts of similiar properties, put in vertical properties

  Gaps were elements that had not yet been discovered

  He was able to work out the atomic mass of the missing elements and so predicted their properties
• Modern periodic table 


  Different in five ways:

  arranged by atomic number not mass number

  there are more elements in our one

  transition metals are in a separate block

  noble gases are included

  some elements have been moved such as hydrogen
• Groups in table


  alkali metals- group 1

  alkaline earth metals- group 2

  halogens- group 7

  noble gases- group 0

  transition metals- large block in middle
• Alkali metals

  • 1 electron in outer shell
  • must be stored under oil to keep air and water away as very reactive
  • soft, shiny grey when freshly cut but tarnishes rapidly
  • metal + oxygen -> metal oxide
  • react vigorously with water to produce metal hydroxide and hydrogen gas
  • skims on waters surface, bubbles/ gas is given off, metal disappears, heat given off
  • indicator turns purple proving it is alkali
  • reactivity increases as you descend
  • M-> M+ + e-
  • white and dissolve in water to give colourless solutions
• Why is potassium more reactive than lithium?

  although they both need to lose one electron to have a full outer shell, potassium’s outer electron is furthest from the positive attractions of the nucleus. Therefore it is easier for potassium to lose its outer electrons than it is for lithium
• Halogens


  • Chlorine
  • Bromine
  • Iodine
  • Fluorine
• Halogens


  • Exist as molecules bonded with their own atoms to add stability
  • Known as diatomic (Cl2, Br2, I2, F2)
• Chlorine


  Green gas and toxic
• Bromine


  Red brown liquid, toxic
• Iodine


  Grey black solid, toxic
• As you descend the group

  Melting and boiling points increase as the intermolecular attraction gets larger
• Halogens


  • All have 7 electrons in the outer shell
• Chlorine gaining an electron

  Cl + e- —> Cl-
• Chlorine molecule gaining two electrons

  Cl2 + 2e- —> 2Cl-
• Fluorine


  Most reactive as the electron it is attempting to attract is coming into a shell closest to the positive nucleus, greater attraction means it is easier to gain an extra electron
• Halogens react with group 1 elements

  Produce a metal halide
• Displacement and reactivity


  If a reactive element comes into contact with the compound of a less reactive element a chemical reaction may take place. The less reactive element is removed from the compound and is replaced by the more reactive element
• Test for chlorine gas 


  Place damp universal indicator paper in gas and if chlorine gas is present then paper changes to red and bleaches white
• Solid iodine sublimes on heating

  iodine (s) —> iodine (g)

  grey black Purple gas
• Why are noble gases unreactive?

  Have a full outer shell, unreactive and stable

  properties- gas at room temp and colourless
• Properties of group 1 elements

  Low mpt

  high reactivity

  soft or liquid so can’t withstand force

  low density

  white or colourless compounds
• Properties of transition metals

  High mpt except mercury

  low reactivity

  strong and hard

  high density

  coloured compounds
• Iron


  Can exist in two forms

  iron (ll) and iron (lll)

  iron oxide can exist in two forms aswell:

  iron ll oxide is black

  iron lll oxide is red brown
• Coloured compounds


  Copper ll oxide is black

  copper ll carbonate is green

  hydrated copper ll sulfate is blue

  copper ll salts are usually blue in solution