The Periodic Table

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  • Created by: Sophie
  • Created on: 28-01-14 13:39

General

General

  • In the Periodic Table the elements are arranged on order of increasing atomic number.
  • The elements in a period show trends in physical and chemical properties that are repeated across the period.
  • The similarity in properties of elements n a group is due to them havinf the same number of outer shell electrons.
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Trends Across Periods 2 and 3

Trends across Periods 2 and 3

  • Electron Configuration:
    • Across the period successive elements have one more outer shell electron.
  • Atomic radius:
    • Decreases going across the period:
      • Bigger nuclear charge
      • Same shielding
      • Nuclear attraction increases
  • 1st ionisation energy:
    • Increases going across the period:
      • Bigger nuclear charge 
      • Same shielding
      • Nuclear attraction increases
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Trends Across Periods 2 and 3 Continued

Trends Across Periods 2 and 3 Continued

  • Melting and Boiling Points:
    • Na, Mg and Al have metallic bond (high melting point).
    • Melting point increases from Na to Mg to Al because metal ion has greater charge.
    • Si has very high melting point (giant covalent structure)
    • P4, S8 and Cl2 have low melting points (simple covalent molecule)
    • Ar has a very low melting points (fewest electrons, weakest van der Waal's forces).
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Trends Down Groups

Trends Down Groups

  • Atomic Radius:
    • It increases going down the group:
      • Extra electron shell
      • Outer electron further from nucleus
      • More shielding
      • Increased nuclear charge (outweighs shielding and distance)
  • 1st Ionisation Energy:
    • It decreases going down the group:
      • Extra electron shell
      • Outer electron further from the nucleus
      • More shielding
      • Increased nuclear charge (outweighs shielding and distance)
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Redox Reactions of Group 2 Metals - Water

Redox Reactions of Group 2 Metals

  • Group 2 elements undergo redox reactions with water and oxygen.

Water

  • Fizzing will be seen (gas released).
  • The group 2 eleetn will dissolve.

Example

Ca(s) + 2H2O(l) ----> Ca(OH)2(aq) + H2(g)

Ca:  0 to +2 = oxidation                  

H:   +1 to 0 = reduction

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Redox Reactions of Group 2 Metals - Oxygen

Redox Reactions of Group 2 Metals - Oxygen

  • Mg burns with a bright white flame.
  • A white powder will be produced.

2Mg + O2 --> 2MgO

Mg:   0 to +2 = oxidation                  

O:     0 to -2 = reduction

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Redox Reactions of Group 2 Metals - Trend in react

Trends in reactivity

  • Reactivity increases down the group.
  • The elements lose 2 outer electrons in these reactions.
  • Down the group the outer electrons are further from nucleus and more shielded.
  • Nuclear attraction is reduced, so electrons are lost more easily.
  • Increased nuclear charge outweighed by greater shielding and distance.
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Reactions of Group 2 Compounds - Oxides

Reactions of Group 2 Compounds - Oxides

  • Adding water (in drops) to CaO produces calcium hydroxide, Ca(OH)2(s).
  • In excess water, calcium hydroxide dissolves to make limewater Ca(OH)2(aq) whose pH is about 12.

Equation

 CaO(s) + H2O(l) ---> Ca(OH)2(s)

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Reactions of Group 2 Compounds - Carbonates

Reactions of Group 2 Compounds - Carbonates

  • Group 2 carbonates decompose when heated.
  • Going down the Group, the carbonates become harder to decompose (i.e. they become more stable.)

Example Equation

MgCO3(s) ---> MgO(s) + CO2(g)

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Reactions of Group 2 Compounds - Hydroxides

Reactions of Group 2 Compounds - Hydroxides

  • Group 2 hydroxides are alkaline and can be used to neutralise acids.
  • Calcium hydroxide (Ca(OH)2), can be used to reduce soil acidity in soil.
  • Magnesium hydroxide (Mg(OH)2), is found in milk of magnesia.
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Boiling Points of the Group 7 Elements

Boiling Points of the Group 7 Elements

  • At room temperature:
    • Cl2 is a pale green gas.
    • Br2 is a brown liquid.
    • I2 is a blue-black solid.
  • In Group 7, melting and boiling point increases down the group:
    • The molecules have more electrons.
    • Stronger van der Waal's forces.
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Redox Reactions of Group 7 Elements - Displacement

Displacement Reactions

  • Reactivity decreases down the group
  • This can be shown when the halogen elements higher up displace elements further down the group.

Colours of the Halogens

  • In water:
    • Cl2 - pale green
    • Br2 - orange
    • I- brown
  • In a organic solvent:
    • Cl2 - pale green
    • Br2 - orange
    • I- violet
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Disproportionation reactions

Disproportionation reactions - Chlorine and Water

  • Chlorine undergoes a redox reaction with water.
  • Cl2(g) + H2O(l) --> HCl(aq) + HOCl(aq)
  • This reaction is used in water purification.
  • The risks of using chlorine:
    • Chlorine gas is toxic.
    • The formation of chlorinated hydrocarbon is possible.
  • The benefits using chlorine:
    • Killing bateria outweighs the risks.

Disproportionation reactions - Chlorine and Dilute Sodium Hydroxide

  • Chlorine undergoes a redox reaction with cold, dilute sodium hydroxide solution.
  • This reaction is used to make bleach.
  • Cl2(g) + 2NaOH(aq) --> NaCl(aq) + NaOCl(aq) +H2O(l)
  • In both reactions the oxidation state of Cl changes from 0 to -1(Cl-) and 0 to +1(OCl-).
  • Cl is oxidised and reduced, this is an example of disproportionation.
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Reactions of Halide Ions (Cl-, Br- and I-)

Reactions of Halide Ions (Cl-, Br- and I-)

  • Chloride ions, bromide ions and iodide ions produce colored precipitates with silver nitrate solution (AgNO3(aq)).
  • Ag+(aq) + Cl-(aq) --> AgCl(s) - white precipitate
  • Ag+(aq) + Br-(aq) --> AgBr(s) - cream precipitate
  • Ag+(aq) + I-(aq) --> AgI(s) - yellow precipitate

Compounds in Ammonia Solution

  • AgCl(s) dissolves in dilute ammonia solution, NH3(aq).
  • AgBr(s) dissolves in concentrated ammonia solution but not in dilute ammonia.
  • AgI(s) does not dissolve, even in concentrated ammonia solution.
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