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Properties and reactions of Period 3 Oxides

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Properties and reactions of Period 3 Oxides

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Na2O (Sodium Oxide)
Reaction with water: Reacts exothermically with cold water to produce NaOH

Reaction with acid: Reacts with dilute hydrochloric acid to produce NaCl solution

MgO (Magnesium Oxide)
Reaction with water: Slight reaction between MgO and H2O to produce Mg(OH)2

Reaction with acid: Reacts with warm dilute HCl to produce MgCl solution

Al2O3 (Aluminium Oxide)
Reaction with water: does not react with water as ions are held too strongly

Reaction with acid: Reacts with hot dilute HCl to produce Al2Cl3 solution

Reaction with base: Reacts with hot concentrated NaOH to give colourless solution of NaAl(OH)4

SiO2 (Silicon Oxide)
Reaction with water: Does not react with water as Si and O atoms are held too strongly by covalent bonds

Reaction with base: Reacts with hot and concentrated NaOH to form Na2SiO3

P4O10 (Phosphorus (V) Oxide)
Reaction with water: Reacts violently with water to form H3PO4 (Phosphoric (V) acid)

Reaction with base: reacts with NaOH to form Na3PO4 (Sodium Phosphate)

SO3 (Sulfur Trioxide)
Reaction with water: Reacts violently with water to produce a fog of sulphuric (VI) acid droplets

Reaction with base: Reacts with NaOH to form Na2SO4 (Sodium Sulfate salt)

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NaCl and MgCl2 are giant ionic lattices. AlCl3 and PCl5 change their structure from ionic to covalent when the solid turns to a liquid or vapour. SiCl4 is a simple covalent molecule.

Aluminum:
At room temp - AlCl3 is solid (ionic lattice with a lot of covalent character)
180-190oC - converts to molecular form AlCl6 (causing it to melt/vapourise due to weak intermolecular attractions btwn molecules
Continues to increase - breaks into AlCl3
AlCl6 --> AlCl3

Phosphorus:
At room temp - PCl5 is white solid (sublimes at 163oC) --> Contains ions which explains the physical state.
Formation of PCl5 involves two molecules
- 2PCl5 --> PCl4+ + PCl6-
At 163oC - PCl5 converts to simple molecular form containing PCl5 molecules (Weak intermolecular attractions exists, therefore vapourises)

Sodium:

Reaction with water

Sodium chloride does not react with water. It simply dissolves in water to give a neutral solution.

Magnesium:

Reaction with water

Magnesium chloride dissolves in water to give a faintly acidic solution (pH ~ 6).

When Mg2+ ions are broken off the solid lattice and go into solution, there is enough attraction between the Mg2+  and H2O molecules to form co-ordinate (dative covalent) bonds.

Hexaaquamagnesium ions, [Mg(H2O)6]2+ are formed.

MgCl2 (s) + 6H2O (l) -->[Mg(H2O)6]2+ (aq) + 2Cl- (aq)

Silicon tetrachloride:

Reaction with water

If water is added to silicon tetrachloride, a violent reaction occurs to produce silicon dioxide and fumes of hydrogen chloride.

In a large excess of water, the hydrogen chloride will dissolve to give a strongly acidic solution containing hydrochloric acid.

SiCl4 (s) + 2H2O (l) --> SiO2 (g) + 4HCl (aq)

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Na, Mg & Al conduct electricity as the delocalized electrons are free to move throughout the structure

Si can only conduct electricity at high temperatures since at room temperature there are no electrons free to move

P, S, Cl, Ar cannot conduct electricity as they are simple molecules with no electrons free to move

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Melting and boiling points in relevance to their structures

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Melting and boiling points in relevance to their structures

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Na, Mg & Al have high melting and boiling points as a lot of energy is required to break the strong metallic bonding between the positive nucleus and sea of electrons

Si has a high melting & boiling point as a lot of energy is required to break the strong covalent bonds between Si atoms

P, S, Cl, Ar have low melting and boiling points as not a lot of energy is required to break the weak Van der Waals forces between the molecules

Trend of highest to lowest melting/boiling point: Al > Si > Mg > Na > S > P > Cl > Ar

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Na, Mg & Al are metals & have metallic structures

Si is a metalloid & has a giant covalent structure

P, S, Cl, Ar are non-metals & form simple molecules

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- Magnesium chloride and Sodium chloride dissolve to form a colorless solution
- Aluminium chloride is insoluble in water. It reacts to form Hexaaquaaluminium ions

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Properties and reaction of period 3 hydroxides

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Properties and reaction of period 3 hydroxides

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Structure

Sodium, Magnesium, Aluminium Oxides form giant ionic lattice structures

Silicon forms giant covalent structures

Phosphorus(V) oxide, Sulfur trioxide forms simple molecular structures

Bonding

Na, Mg, Al oxides are bonded ionically

Si, P, S oxides are covalently bonded

Acid-Base Behaviour

Sodium, Magnesium oxides are basic

Aluminium oxides are amphoteric

Sulfur dioxide, Phosphorus (V) oxide, Sulfur trioxide are acidic