Advanced Higher Advanced Higher ChemistryChemistry

Unit 1 Unit 1

The oxides, chlorides and The oxides, chlorides and hydrideshydrides

Metal oxides Metal oxides

Oxygen is highly electronegative and Oxygen is highly electronegative and readily reacts with metals to form ionic readily reacts with metals to form ionic metal oxides.metal oxides.

Ionic metal oxides tend to be basic i.e. Ionic metal oxides tend to be basic i.e. they dissolve in water to form alkalis.they dissolve in water to form alkalis.

The reaction of sodium oxide (sodium hThe reaction of sodium oxide (sodium hydroxide, ydroxide, NaOHNaOH) with water.) with water.

The reaction of magnesium oxide (The reaction of magnesium oxide (MgOMgO) with water.) with water.

Non-metal oxidesNon-metal oxides Oxygen reacts with non-metals to form Oxygen reacts with non-metals to form

covalent or polar covalent molecules. covalent or polar covalent molecules. Soluble covalent oxides dissolve in water to Soluble covalent oxides dissolve in water to

form acids. The exception is carbon monoxide form acids. The exception is carbon monoxide which is neutral.which is neutral.

The reaction of The reaction of phosphorus(Vphosphorus(V) oxide (P) oxide (P44OO1010

) with water.) with water. The reaction of sulphur dioxide The reaction of sulphur dioxide (SO(SO22

) with water.) with water. Non-metal oxides tend to be gases and exist Non-metal oxides tend to be gases and exist

as discrete molecules.as discrete molecules.

Silicon oxideSilicon oxide

Oxygen reacts with silicon to form silicon Oxygen reacts with silicon to form silicon dioxide, a giant covalent network.dioxide, a giant covalent network.

The ratio of silicon atoms to oxygen atoms The ratio of silicon atoms to oxygen atoms is 1: 2 so the formula SiOis 1: 2 so the formula SiO22 is the simplest is the simplest formula rather than the actual molecular formula rather than the actual molecular formula.formula.

SiOSiO2 2 is not soluble in water but will is not soluble in water but will dissolve in alkalis to form the silicate ion dissolve in alkalis to form the silicate ion and so it can be said to be an acidic oxide.and so it can be said to be an acidic oxide.

Melting Points/Boiling Melting Points/Boiling PointsPoints

In general, the melting and boiling In general, the melting and boiling points of the oxides decrease from points of the oxides decrease from very high to very low across a period.very high to very low across a period.

Oxides to the left of the Periodic Oxides to the left of the Periodic Table are ionic lattices.Table are ionic lattices.

Oxides to the right are discrete Oxides to the right are discrete covalent molecules, the exception covalent molecules, the exception being SiObeing SiO22..

Electrical ConductivityElectrical Conductivity

Ionic metal oxides will only Ionic metal oxides will only conduct when molten or in solution conduct when molten or in solution when the ionic lattice is broken when the ionic lattice is broken down and the ions are free to down and the ions are free to move.move.

Covalent non-metal oxides do not Covalent non-metal oxides do not conduct.conduct.

Reaction of Oxides with Reaction of Oxides with Acids/BasesAcids/Bases

Some oxides react with acids (basic Some oxides react with acids (basic oxides - Lioxides - Li22O, NaO, Na22O) to produce salts.O) to produce salts.

Acidic oxides (COAcidic oxides (CO22, Cl, Cl22O) react with O) react with bases to produce salts.bases to produce salts.

Amphoteric oxides (BeO, AlAmphoteric oxides (BeO, Al22OO33) can react ) can react with acids or bases to produce salts. with acids or bases to produce salts.

Chlorides Chlorides

Chlorine is also a very Chlorine is also a very electronegative element but is electronegative element but is less electronegative than less electronegative than oxygen.oxygen.

The chlorides have very similar The chlorides have very similar periodic properties to the periodic properties to the oxides.oxides.

Metal chloridesMetal chlorides The metal chlorides tend to be made by The metal chlorides tend to be made by

combining the metal directly with chlorine combining the metal directly with chlorine of by reacting the metal with hydrogen of by reacting the metal with hydrogen chloride.chloride.

Generally ionic chlorides dissolve in water, Generally ionic chlorides dissolve in water, but do not react with water, and can be but do not react with water, and can be recovered chemically unchanged. AlClrecovered chemically unchanged. AlCl33 is an is an exception to this rule.exception to this rule.

Sodium chloride crystals dissolvingSodium chloride crystals dissolving AlClAlCl33 has covalent molecular bonding and has covalent molecular bonding and

reacts with water to form fumes of reacts with water to form fumes of hydrogen chloride gas.hydrogen chloride gas.

Non-metal chloridesNon-metal chlorides

Some covalent chlorides react with Some covalent chlorides react with water to produce fumes of HCl water to produce fumes of HCl e.g. e.g. PClPCl55(s) + 4H(s) + 4H22O(l) O(l) H H33POPO44(aq) + 5HCl(aq)(aq) + 5HCl(aq)

Note this produces a strongly acidic solution.Note this produces a strongly acidic solution. Hydrolysis of phosphorus trichlorideHydrolysis of phosphorus trichloride Properties of chlorides of third period Properties of chlorides of third period

elementselements

Hydrides Hydrides

Hydrogen has an electronegativity Hydrogen has an electronegativity value of 2.2. It forms ionic metal value of 2.2. It forms ionic metal hydrides with metals in Groups 1 hydrides with metals in Groups 1 and 2.and 2.

Hydrides contain the HHydrides contain the H-- ion. ion. Hydrides are colourless solids.Hydrides are colourless solids.

The hydride ion is a strong base and will The hydride ion is a strong base and will remove a hydrogen ion from a water remove a hydrogen ion from a water molecule i.e. they react with water to molecule i.e. they react with water to produce hydrogen gas and hydroxide produce hydrogen gas and hydroxide ionsions

e.g. e.g. 2NaH(s) + 2H2NaH(s) + 2H22O(l) O(l) H H22(g) + 2NaOH(aq)(g) + 2NaOH(aq)

Ionic hydrides can be used as drying Ionic hydrides can be used as drying agents and as reducing agents e.g. agents and as reducing agents e.g. LiAlHLiAlH44 and NaBH and NaBH44..

Electrolysis of molten hydrides will Electrolysis of molten hydrides will produce Hproduce H22 gas at the positive electrode gas at the positive electrode

i.e.i.e. 2H2H-- H H22 + 2e + 2e--

Because hydrogen is not very Because hydrogen is not very electronegative, most hydrides are electronegative, most hydrides are covalent with typical covalent covalent with typical covalent properties.properties.