HL periodicity

Bonding of the period 3 oxides Formula of oxide Na2O(s) MgO(s) Al2O3(s) SiO2(s) P4O10(s) P4O6(s) SO3(l) SO2(g) Cl2O7(l) Cl2O(g) Oxidation number +1 +2 +3 +4 +5/+3 +6/+4 +7/+1 Electrical conductivity in molten state   High Very low None Structure Giant ionic Giant covalent Molecular covalent

Bonding of the period 3 chlorides Formula of chloride NaCl(s) MgCl2(s) AlCl3(s) Al2Cl6(g) SiCl4(l) PCl5(s) PCl3(l) S2Cl2(l) Cl2(g) Oxidation number +1 +2 +3 +4 +5/+3 Electrical conductivity in molten state   High Poor None Structure Giant ionic Molecular covalent Al2Cl6 is known as a dimer with dative covalent bonds between the Cl and Al atoms.

Reaction of chlorine with water This is an example of a disproportionation reaction (the chlorine is both oxidized and reduced). The hyperchlorous acid decomposes to HCl(aq) and O2(g) This reaction is used in the purification of water.

Hydration of ionic compounds NaCl forms a neutral solution – the charge density of the Na+ is not high enough to hydrolyse water molecules. MgCl2 forms a slightly acidic solution (pH 6) as it has a higher charge density than the Na+ ion.

Hydrolysis of aluminium chloride The Al3+ ion has a high charge density which attracts water molecules. The water molecules form dative covalent bonds with the Al3+ ion to form an octahedral complex ion [Al(H2O)6]3+ The water molecules are known as ligands, which have a lone pair of electrons and bond to the central ion by a dative covalent bond.

The high charge density of the Al3+ ion attracts the electrons of the O-H bond in the water molecules and releases a H+ ion to form an acidic solution.

Hydrolysis of silicon and phosphorus chlorides Silicon chloride reacts with water to form HCl(aq) and insoluble silicon dioxide. Both chlorides of phosphorus also produce acidic solutions due to the formation of HCl(aq) and phosphoric (III) or (IV) acid.

Characteristic properties of transition metals Physical properties: High electrical and thermal conductivity. High melting point. Malleable – they are easily bent into different shapes. High tensile strength. Ductile – they can be made into wires.

Chemical properties: They form compounds with more than one oxidation state (variable oxidation states). Form complex ions. Form colored compounds. Act as catalysts (speed up the rate of a chemical reaction by lowering Ea)

Transition metals Definition of transition metals: Transition metals form one or more positive ions with a partially filled d sub-level. Scandium and zinc are d-block elements, but they are not transition metals.

The Sc3+ ion and Zn2+ ion do not have a partially filled d sub-level, therefore they are not classed as transition metals. They do not show any characteristics of transition metals; they do not form colored compounds, they do not have variable oxidation states and they do not act as catalysts.

Variable oxidation states A characteristic chemical property of the transition metals is that they have variable oxidation numbers. All transition metals can have an oxidation number of +2, as they lose the 4s electrons first.

Variable oxidation states A characteristic chemical property of the transition metals is that they have variable oxidation numbers. All transition metals can have an oxidation number of +2, as they lose the 4s electrons first.

Variable oxidation states A characteristic chemical property of the transition metals is that they have variable oxidation numbers. All transition metals can have an oxidation number of +2, as they lose the 4s electrons first.

Comparison of ionisation energy in Ca and Cr Ca has a large increase in ionisation energy when the 3rd electron is removed, whereas Cr shows a large increase when the 7th electron is removed. This is due to the closeness in energy of the 3d and 4s sub-levels. Ca 1s2 2s 2p6 3s2 3p6 4s2 Cr 1s2 2s 2p6 3s2 3p6 4s1 3d5

Ligands A ligand is a species that uses a lone pair of electrons to form a dative covalent bond with a metal ion.

Complex ions A complex ion has a metal ion at the centre with a number of other molecules surrounding it. These molecules are called ligands (species with a lone pair of electrons that form a dative covalent bond with a metal ion). Ligands bond to the metal ion by dative covalent bonds. Hexaaquaaluminium (III) ion

Complex ions Shape: linear Coordination number: 2 Shape: square planar Shape: tetrahedral Coordination number: 4 Shape: octahedral Coordination number: 6

Complex ions Diaminesilver(I) ion Oxidation state of Ag is +1 Coordination number 2 Linear Hexaaquairon(III) ion Oxidation state of Fe is +3 Coordination number 6 Octahedral Hexacyanoferrate(III) ion Oxidation state of Fe is +3 Coordination number 6 Octahedral Tetrachlorocuprate(II) ion Oxidation state of Cu is +2 Coordination number 4 Tetrahedral

Colour of transition metal complex ions

Colour of complex ions Lone pairs of electrons on the ligands cause the d orbitals to split into two sets. Hexaaquairon(III) ion Oxidation state of Fe is +3 Coordination number 6 Octahedral Degenerate d orbitals.

Colour of complex ions Transition metals have partially filled d sub-levels. The d orbitals are split into two sets with different energies (by the lone pairs of electrons on ligands). Electrons can transition from lower to higher sets of d orbitals by absorbing energy. The energy absorbed corresponds to frequencies of visible light. The remaining frequencies of light which are not absorbed results in the colour that is seen.

Factors that affect the colour of complex ions The identity of the central metal ion. The charge density of the ligand. The oxidation number of the central ion. The shape of the complex ion.

Transition metals as catalysts MnO2 in the decomposition of hydrogen peroxide. V2O5 in the Contact process. Fe in the Haber process and in heme. Ni in the conversion of alkenes to alkanes. Co in vitamin B12 Pd and Pt in catalytic converters.

Economic significance of catalysts Fe in the Haber process and V2O5 in the Contact process Catalysts lower the activation energy for a chemical reaction. The rate of the forward and backward reaction is increased equally. A catalyst won’t increase the yield but will allow equilibrium to be reached quicker which has an economic benefit.