Periodicity (AHL)Year 11 DP ChemistryRob Slider

Oxides of Period 3

Na2O MgO Al2O3 SiO2 P4O10 SO3 Cl2O7

P4O6 SO2 Cl2O

What patterns are there in the following properties?• Structure• Melting/boiling points• Electrical conductivity• Acidity

Oxide structure

Al2O3 forms bonds that have ionic

and covalent character

Oxides of Na, Mg form ionic bonds,

so they have ionic

lattices

SiO2 forms a giant

covalent macromolec

ular structure

Oxides of P, S, Cl form

simple covalent

molecular substances

Oxide melting/boiling points

Oxides of Na, Mg, Al

Ionic compounds have high mp/bp

SiO2

The diamond-like covalent

macromolecular structure leads to a high mp/bp

Oxides of P, S, Cl Simple covalent

molecular substances have

weaker intermolecular

forces and much lower mp/bp

Oxide electrical conductivity

Oxides of Na, Mg, Al

Ionic compounds form ions when molten and will

conduct electricity

SiO2

The diamond-like covalent

macromolecular structure has

fixed electrons and will not

conduct electricity as a liquid or a solid

Oxides of P, S, Cl Simple covalent

molecular substances do not have any free electrons

and do not conduct

electricity

Oxide acidity

Oxides of Na, MgReact with water

to form basic solutions

Oxides of Al Acts as both an acid and a base

Amphoteric

Oxides of Si, P, S, Cl

SiO2 reacts with NaOH (i.e. acts as

an acid)The other oxides react with water

to form acidic solutions

Na2O(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 3

NaCl MgCl2 Al2Cl6 SiCl4 PCl3 S2Cl2 Cl2

PCl5

What patterns are there in the following properties?• Structure• Melting/boiling points• Electrical conductivity• Acidity

Chloride structure

Chlorides of Na, Mg, form ionic bonds, so they

have ionic lattices

Chlorides of Al form bonds with

ionic and covalent

character, so they form lattices

as a solid and sublime to a gas

Chlorides of Si,P, S form simple

covalent molecular

substances

Chloride melting/boiling points

Chlorides of Na, Mg

Ionic compounds have high mp/bp

Chlorides of Al Aluminium

chloride sublimes at

1780C to form gaseous

molecules of Al2Cl6

Chlorides of Si,P, S

Simple covalent molecular

substances have weaker

intermolecular forces and much

lower mp/bp

Chloride electrical conductivity

Chlorides of Na, Mg

Ionic compounds form ions when molten and will

conduct electricity

Al There is no ionic character when

solid and molecules form above 1780C, so

no electrical conductivity

Chlorides of Si, P, S

Simple covalent molecular

substances do not have any free electrons

and do not conduct

electricity

Chloride acidity

NaClThis forms a

neutral solution in

water

MgWeakly acidic

Chlorides of Al, Si, P, SThese all

react vigourously

with water to form acidic HCl fumes

Cl2Chlorine gas reacts to a

small extent with water to

form an acidic

solution

NaCl(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-block

The 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 electrons

A 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 TM

Due to the partially filled d-subshell, TM have unique properties including:

•Multiple oxidation states

•Complex ion formation

•Formation of coloured compounds

•Catalytic properties

Electronic configurations

Sc [Ar] 3d14s2

Ti [Ar] 3d24s2

V [Ar] 3d34s2

Cr [Ar] 3d54s1

Mn [Ar] 3d54s2

Fe [Ar] 3d64s2

Co [Ar] 3d74s2

Ni [Ar] 3d84s2

Cu [Ar] 3d104s1

Zn [Ar] 3d104s2

As 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 energy

Sc and Zn (not TM)

Zn has a configuration of [Ar]3d104s2,

The Zn2+ ion ([Ar] 3d10), therefore is not a typical TM ion

Sc forms Sc3+ which has the stable configuration of Ar

Sc3+ has no 3d electrons, therefore it is not considered to be a TM

Variable 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 electrons

Variable oxidation states

Due to the similar energy levels of the 4s and 3d, other oxidation states in addition to +2 are also possible.

On the left, all of the electrons

from the 4s and 3d can be lost forming ions

such as Sc3+ and Ti4+. This

represents the largest possible

OS

On the right, the nucleus has a

stronger pull on the outer

electrons due to a greater

positive charge. This means that +2 is the most stable as there

is a greater energy

difference between the 3d and 4s(Co, Ni,

Cu)

Cu also forms +1 due to the formation of the stable [Ar]3d10

In 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 state

Chromium Manganese Iron

+7 MnO4-

permanganate

+6 CrO42- chromate

Cr2O72-

dichromate

+5

+4 MnO2

+3 Cr3+ Fe3+

Summary of oxidation states

Boxed states are the important ones to know

Sc

Ti V Cr

Mn

Fe

Co

Ni

Cu

Zn

+1

+2 +2 +2 +2 +2 +2 +2 +2 +2

+3 +3 +3 +3 +3 +3 +3 +3 +3

+4 +4 +4

+5

+6 +6 +6

+7

Summary of 1st d-block OS

Higher OS’s become less stable relative to lower ones on moving from left to right across the series(stronger + nuclear force)

Compounds containing

TM’s in high OS’s 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 electrons

The 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

Complex 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 geometry

2-coord complexes form linear geometries

4-coord complexes form tetrahedral or square planar geometries

6-coord complexes tend to form octahedral geometries

Complex compounds

Complex 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.

How 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?? Let’s look at an example:

Fe(H2O)6 3+

Fe: 1s22s22p63s23p63d64s2

Fe3+: 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]+

Optical 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.

Coloured complexesMany d-complexes are coloured. These characteristic colours are specific to individual ions and depend upon:

•Metal oxidation state•Ligands attached•Coordination number/shape

Same metal/different OS

Same metal/different ligand Same metal/different

coord

Why 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.

d,d transitionsMovement between the d-orbitals by the e- represents an energy change, ΔE.

Remembering ΔE=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?

Hexa-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 catalysts

Transition metals and their compounds function as catalysts due to:• their ability to change oxidation state• In the metal’s 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

Catalyst 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) oxide

Nickel 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) oxide

Enzymatic 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 gases

Economic significance of Contact Process

The 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 country’s chemical industry. The more healthy the chemical industry, the more healthy industry is in general.

Economic significance of Haber Process

The Haber Process is the production of ammonia from it’s gaseous elements. Ammonia is important to an economy for many reasons. This demonstrates a country’s 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.