The periodic table

1.2.1 The periodic table

Arrangement – order of increasing atomic no

• Elements with similar properties are in columns, aka groups

Why is the table called periodic table?

• Similar properties occur at regular intervals
• Why are the elements in the same group?
  • Same no of e- on outer shell
  • Similar chemical & physical properties
  • 1.2.2 Development of the periodic table
    1. Antoine Lavoisier – has compounds
    2. John Newlands 
    • Arranged strictly in octaves by atomic weights (but no chemical properties)
    • Realised every 8^th element reacts in similar way – ‘Law of octaves’
    • 3. Dimitri Mendeleev
    • Arranged in order of atomic mass but changed some order base on atomic weight
      •        Isotopes proved correct
      • Left gaps for elements that he though hadn’t been discovered
      • Why Mendeleev left gaps?
        • For undiscovered elements so elements with similar properties can be placed tgt / pattern fit
        • Predicted properties of missing elements
      • Later on, elements discovered properties matches predictions
      • 4.Modern – organized in atomic no
      • 1.1.1  Metals and non-metals
      • Properties

1.2.4  Group 0 (Noble gases)

Properties

• Non-metal
• Colorless gases, low melting point, low density, not flammableWhy are elements in group 0 unreactive & don’t form molecules easily? (1)
  • Have full & stable outer shell

  Why does the boiling point increase down the group? (3)

  • ↑ no of shell / size of atom
  • Intermolecular force between atom become stronger
  • Need more energy to overcome force
  • • 1.2.5 Group 1 (Alkali metals)
    • Metals
    • Soft, low melting point, less dense (so top 3 elements float on water)
    • +1 ion → lose e- → form ionic compound
      • White solids, dissolve in water, form colourless solutions
      • Reaction with oxygen
      • Metal_(s) + oxygen_(g) → metal oxide_(s)

      • Metal	Equation	Flame colour
        Lithium	Lithium + oxygen → lithium oxide 4Li + O2 → 2Li2O	Crimson red
        Sodium	Sodium + oxygen → sodium oxide 4Na + O2 → 2Na2O	Yellow
        Potassium	Potassium + oxygen → potassium oxide 4K + O2 → 2K2O	Lilac

      • Reaction with chloride
        • Exothermic reaction
        • Form ionic salt
        • Metal_(s) + chlorine_(g) → metal chloride_(s)

        • Metal	Equation
          Lithium	Lithium + chlorine → lithium chloride 2Li + Cl2 → 2LiCl
          Sodium	Sodium + chlorine → sodium chloride 2Na + Cl2 → 2NaCl
          Potassium	Potassium + chlorine → potassium chloride 2K + Cl2 → 2KCl

        • Reaction with water
        • Metal_(s) + water_(l) → metal hydroxide_(aq) + hydrogen_(g)

Why does the reactivity increase down the group? (4)

• ↑ no of shell
• ↑ electron shielding
• ↓ attraction between +ve nucleus & -ve outer e-
• Outer e- requires less energy to remove
• Atom is more reactive
• 1.2.6 Group 7 (Halogens)
• Non-metals
• Consist of diatomic molecules (2 elements chemically combined using covalent bond)
• -1 ion → gain e- → fill outer shell → stable
• Form molecular compounds with non-metallic elements
• Low melting point → coz weak force between molecules
• Density, melting point increases down the group
• Why does the reactivity decrease down the group? (4)
  • ↑ no of shell
  • ↑ size → e- further from nucleus
  • ↑ electron shielding
  • ↓ attraction between +ve nucleus & -ve outer e-
  • ↓ energy to attract e- to form -ve ion
  • e- easily gained
  • Atom is less reactive

  • Halogen	Appearance & state at room temp	Colour in water
    Fluorine	Yellow gas	_
    Chlorine	Pale yellow – green gas	Pale green
    Bromine	Red – brown liquid	Orange
    Iodine	Purple – black solid	Brown

  • Displacement reaction
  • • More reactive displace less reactive elements
    • F > Cl > Br > I
    • More reactive(s) + compound(aq) → less reactive(s) + compound(aq)

    • 	KI	KBr
      Cl2	Orange 2KI + Cl2 → 2KCl + I2 2I– + Cl2 → 2Cl– + I2	Pale yellow 2KBr + Cl2 → 2KCl + I2 2Br– + Cl2 → 2Cl– + I2	×
      Br2	Yellow orange 2KI + Br2 → 2KCl + I2 2I– + Br2 → 2Cl– + I2	×	Displaced (no reaction)
      I2	×	Displaced (no reaction)	Displaced (no reaction)