Module Five [[Periodicity]] Period Three Oxides and Chlorides

Oxide: Na2O

Structure and Bonding: Giant Ionic

Melting Point: 1275 degress celcius

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* High melting point as Giant ionic lattice so lots of bonds to break

* Actual m.p. influenced by size and charge of ions

* size of metal ion decreases across the period and the charge increases across period, which causes strong electrostatic forces of attraction so melting point increases.

* conducts electricity when molten

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* Acts as a base, so react with acids to for salt and water

Na2O + H2SO4 ----> Na2S04 + H2O

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* Dissolves exothermically in water

* solution has high pH of 13

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Chloride: NaCl

Structure and Bonding: giant Ionic

melting point: 801

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* Giant Ionic structure = high melting point

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* dissolves in watere forming aqueous ions

NaCl + water ---> Na+ + Cl-

* no hydrolysis

* neutral solution: pH = 7

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Oxide: MgO
Structure and Bonding: Giant Ionic
Melting Point: 2852 degress celcius

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* Giant ionic structure = high melting point

* conducts electricity when molten

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* acts as a base so reacts with acid to form salt and water

MgO + 2HCl ----> MgCl2 + H2O

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* Sparingly soluble in water

* Limited hydrolysis occurs

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Chloride: MgCl2
Structure and Bonding: giant Ionic
melting point:714

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* Giant Ionic Structure = High melting point

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* Slight Hydrolysis in water, so pH is about 6

MgCl2 + water ----> Mg2+ + 2Cl

To be continued