Periodicity (AHL)

Periodicity (AHL)Year 11 DP ChemistryRob SliderOxides of Period 3Na2OMgOAl2O3SiO2P4O10SO3Cl2O7P4O6SO2Cl2OWhat patterns are there in the following properties?StructureMelting/boiling pointsElectrical conductivityAcidityOxide structureOxide melting/boiling pointsOxide electrical conductivityOxide acidityNa2O(s) + H2O(l) 2Na+(aq) + 2OH-(aq)Al2O3(s) + 6HCl(aq) 2AlCl3(aq) + H2O(l)Al2O3(s) + 2NaOH(aq) +3 H2O(l) 2NaAl(OH)4(aq) SiO2(s) + 2NaOH(aq) Na2SiO3(aq) + H2O(l)

SO2(g) + H2O(l) H2SO3(aq) P4O10(s) + 6H2O(l) 4H3PO4(aq) Cl2O7(s) + H2O(l) 2HClO4(aq)

Chlorides of period 3NaClMgCl2Al2Cl6SiCl4PCl3S2Cl2Cl2PCl5What patterns are there in the following properties?StructureMelting/boiling pointsElectrical conductivityAcidityChloride structureChloride melting/boiling pointsChloride electrical conductivityChloride acidityNaCl(aq) 2Na+(aq) + 2Cl-(aq)

AlCl3(s) + 3H2O(l) Al2O3(aq) + 6HCl(aq)SiCl4(s) + 4H2O(l) Si(OH)4(aq) + 4HCl(aq)Cl2(g) + H2O(l) HCl(aq) + HClO(aq)

First row d-blockThe d-block elements are in the middle of the Periodic Table and include the transition metals. Starting in period 4 after the 4s fills, the 3d subshell begins to fill with electronsA transition metal (TM) is an element that has at least one ion with a partially filled d-subshell. Not all d-block elements are TM. Sc and Zn are not considered to be TM (more later...)

Properties of TMDue to the partially filled d-subshell, TM have unique properties including:Multiple oxidation statesComplex ion formationFormation of coloured compoundsCatalytic propertiesElectronic configurationsSc[Ar] 3d14s2Ti[Ar] 3d24s2V[Ar] 3d34s2Cr[Ar] 3d54s1Mn[Ar] 3d54s2Fe[Ar] 3d64s2Co[Ar] 3d74s2Ni[Ar] 3d84s2Cu[Ar] 3d104s1Zn[Ar] 3d104s2As we have seen previously, the configurations of the first row d-block mostly fill the 3d subshell in order.

The exceptions come from Cr and Cu where we see more stable configurations from the half-filled and filled 3d subshell.

This is possible because the 4s and 3d subshells are so similar in energySc and Zn (not TM)Zn has a configuration of [Ar]3d104s2,

The Zn2+ ion ([Ar] 3d10), therefore is not a typical TM ionSc forms Sc3+ which has the stable configuration of Ar

Sc3+ has no 3d electrons, therefore it is not considered to be a TMVariable oxidation states+2All transition metals can form the oxidation state of +2 due to the loss of the two s-electrons. In the first row, the 4s.

This is because the 4s fills first, but when ions are being formed, the 4s electrons are also lost first.Examples:

To write the electronic structure for Co2+:Co [Ar] 3d74s2 Co2+ [Ar] 3d7

The 2+ ion is formed by the loss of the two 4s electrons

To write the electronic structure for V3+:V [Ar] 3d34s2 V3+ [Ar] 3d2

The 4s electrons are lost first, then one of the 3d electronsVariable oxidation statesDue to the similar energy levels of the 4s and 3d, other oxidation states in addition to +2 are also possible.Cu also forms +1 due to the formation of the stable [Ar]3d10In the middleV, Cr, Mg, Fe

It requires too much energy to remove all of the electrons from these elements as the number of valence electrons and high nuclear charge increases.

What often occurs is the formation of more stable oxyanions, such as VO3-, vanadate(V). Some important ones to remember:Oxidation stateChromiumManganeseIron+7MnO4- permanganate+6CrO42- chromate Cr2O72- dichromate+5+4MnO2 +3Cr3+Fe3+Note there are other oxidation states possible for these elements. For example Mn can also form +3 (Mn2O3), +6(MnO4 2-). However, the IB course does not specifically require knowledge of these states. Simple ions with high OSs such as V5+ & Mn7+ are not formed

18Summary of oxidation statesBoxed states are the important ones to knowScTiVCrMnFeCoNiCuZn+1+2+2+2+2+2+2+2+2+3+3+3+3+3+3+3+3+3+4+4+4+5+6+6+6+7Summary of 1st d-block OSHigher OSs become less stable relative to lower ones on moving from left to right across the series(stronger + nuclear force)

Compounds containing TMs in high OSs tend to be oxyanions and oxidising agents e.g. MnO4-

On the left, +2 state highly reducing.

e.g. V2+(aq) , Cr2+(aq) are strong reducing agents (lose e- easily)On the right, +2 is more common; +3 state highly oxidising.

E.g. Co3+ is a strong oxidising agent (gain e- easily), Ni3+ & Cu3+ do not exist in aqueous solution.Complex ion formationComplex ions have a metal ion at the centre with a number of other molecules or ions surrounding it.

These are some common ligands found in complex ion formation. Notice they all have lone pairs of electronsThe bonds are coordinate bonds where a lone pair on a molecule/ion is donated to a low energy, unfilled metal orbital such as a d-orbital. These molecules/ions are called ligands.Ligands are neutral molecules or anions that contain a non-bonding pair of electrons Due to coordinate bonds, these compounds are also referred to as coordinate complexes. In addition to the ligands above, CN- is also another important one.21Complex ionsCoordination number:The most common complex ions contain 4 or 6 ligands. These are known as 4-coordinated and 6-coordinated. 2 is also possible.Water forms hexahydrated complex ions (6-coordinated) with most transition metals.Example: [Fe(H2O)6]3+Many complex ions form coloured solutions

The charge on the complex is the sum of the metal and the ligands. The Cr is 2+ and the water is neutral leading to a 2+ complex ion charge. You try:Fe(III) + CN- (6-coord)Cu (II) + Cl- (4-coord)Ag+ + NH3 (2-coord)

Complex ion geometry2-coord complexes form linear geometries4-coord complexes form tetrahedral or square planar geometries6-coord complexes tend to form octahedral geometries

Source of atom diagrams: http://chemistry.about.com/od/atomicmolecularstructure/ig/VSEPR-Molecular-Geometry/Tetrahedral-Molecular-Geometry.htm

23Complex compoundsComplex ions can be anions or cations and will bond with oppositely charged ions to make salts. Notice how [Cu(NH3)4]2+ is formed:

This complex ion can then bond with Cl- to form [Cu(NH3)4]Cl2

(CuCl4)2- is an anion that can form a compound with K+ to form [K2(CuCl4)]Would you expect these two compounds to be soluble in water?Yes, they are soluble in water.Some complexes do not form ions because the charges on the metal and the ligand cancel each other. Example: [Pt(NH3)2(Cl)2]24How does the metal attract so many ligands??You may be wondering why a metal ion will attract more ligands than it has charges. +2 should attract -2 and +3 should attract -3, right?? Lets look at an example:Fe(H2O)6 3+Fe: 1s22s22p63s23p63d64s2Fe3+: 1s22s22p63s23p63d5In Fe3+, the 4s is now empty and there are 5 unpaired e-. You might expect 5 ligands, but the ion uses six orbitals from the 4s, 4p and 4d to accept lone pairs from six water molecules. It hybridises six new orbitals all with the same energy.Why not 4 or 8? Six is the maximum number of water molecules it is possible to fit around an iron ion (and most other metal ions). By making the maximum number of bonds, it releases most energy and so becomes most energetically stable.

Isomers (cis,trans)Metal complexes sometimes have more than one type of ligand attached. This leads to possible isomerism with complexes having different ligand arrangements. These are called stereoisomers.cisWhen ligands are adjacent to each other they are said to be cis-transWhen ligands are opposite to each other they are said to be trans-cis-[CoCl2(NH3)4]+trans-[CoCl2(NH3)4]+

Molecule diagram source: http://en.wikipedia.org/wiki/Coordination_complex 26Optical isomersSome isomers are mirror images of one another. Therefore, they cannot be superimposed on one another. These two mirror image compounds are known as optical isomers or enantiomers.

Easiest way to visualise this is to look at the human hands which are mirror images of each other. They are called optical isomers because they rotate the plane of polarised light. Chemically, they behave the same unless they are interacting with other optically active molecules. Extension: the complexes above show bidentate ligands (attached at 2 locations on the metal). Monodentate is all that is required for IB DP27Coloured complexesMany d-complexes are coloured. These characteristic colours are specific to individual ions and depend upon:Metal oxidation stateLigands attachedCoordination number/shape

Same metal/different OSSame metal/different ligandSame metal/different coordSource of diagrams: http://www.docbrown.info/page07/appendixtrans04.htm28Why coloured? d,d transitions

The d-orbitals shown above, have various arrangements around the x, y and z axes. When a 6-coord complex is formed with a d-block element, the ligands will approach along the axes of an octahedral, to minimise repulsions of bonding e-.The approach of the ligands raises the energy level of the d-orbitals, but the orbitals that lie on the axes (4,5 above) will experience more repulsion and thus will be a slightly higher energy level (than 1,2,3).This means the d orbitals are split.

Source of diagrams: http://www.docbrown.info/page07/appendixtrans04.htm

29d,d transitions

Movement between the d-orbitals by the e- represents an energy change, E.

Remembering E=hv, a transition between d-orbitals represents a specific frequency that is specific to a complex.Considering the four d-block elements above, only 2 and 3 have possible transitions. They are coloured due to the excitation of e- to higher d-orbitals. This transition absorbs specific frequencies and we perceive the remaining frequencies.

Why are Sc3+ and Zn2+ colourless?Perceived colour example: Copper (II) complexes are often blue-green due to the red frequencies being absorbed30Hexa-aqua complex colours

This shows the colours of 6-coord aqua complexes of the first row d-block. Exceptions are Cu(I) which only forms simple colourless compounds and Cu(II) which forms a 4-coord aqua complex [Cu(H2O)4]2+ . Notice there are no possible transitions for Sc3+ and Zn2+, so they are typically colourless.Complex colours-examples

TM as catalystsTransition metals and their compounds function as catalysts due to:their ability to change oxidation stateIn the metals ability to adsorb other substances on to their surface and activate them in the process.Iron in the Haber ProcessThe Haber Process combines hydrogen and nitrogen to make ammonia using an iron catalyst.

Nitrogen and hydrogen molecules are adsorbed on to the metallic iron surface. The hydrogen almost immediately splits into its component atoms by sharing or exchanging electrons with the catalyst surface

Source of digram: http://www.spaceflight.esa.int/impress/text/education/Catalysis/Commercial.html33Catalyst examples

V2O5 in the Contact ProcessThis is the conversion of sulfur dioxide to sulfur trioxide by passing the gaseous reactants over a solid vanadium (V) oxideNickel in the hydrogenation of C=C bondsThis reaction see the conversion of alkenes to alkanes

MnO2 in the decomposition of hydrogen peroxideThis speeds up the spontaneous decomposition of hydrogen peroxide by manganese (IV) oxideEnzymatic catalysisFe in haemoglobin for carrying oxygenCo in vitamin B12 to help produce red blood cells See (Green, p92 for structures)Catalytic convertersPt and Pd are used to convert NOx and CO to harmless gasesEconomic significance of Contact ProcessThe Contact Process is used in the manufacture of sulfuric acid. Sulfuric acid is used in many industrial processes such as the manufacture of polymers, fertilisers and detergents. It is also used in mining and petrochemicals industries.Many experts point to the amount of sulfuric acid production as a good indication of the health of a countrys chemical industry. The more healthy the chemical industry, the more healthy industry is in general.

Economic significance of Haber ProcessThe Haber Process is the production of ammonia from its gaseous elements. Ammonia is important to an economy for many reasons. This demonstrates a countrys ability to take readily available raw materials and turn them into useful products. Importantly, it is used in fertilisers which is vital in helping to feed the populations.

It is also used in the manufacture of explosives. Developed during WWI, this helped Germany prolong the war.It is also used in the production of polymers such as nylon, which is used to make a variety of materials from clothing to toothbrushes to parachutes.