Periodicity (AHL) Year 11 DP Chemistry Rob Slider.
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Transcript of Periodicity (AHL) Year 11 DP Chemistry Rob Slider.
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
+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.