Carbon tetrachloride or tetrachloromethane has a molecular structure. The molecules have a tetrahedral shape as the central carbon atom is surrounded by 4 bonding pairs of electrons.
Task
4.2b(iii) Draw SiCl4.| Period 3 Elements |
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| Reaction with Oxygen => |
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| Reaction with Chlorine => |
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| Reaction with Water => |
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HCl |
| Acidity/Alkalinity of Oxides | basic |
basic
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acidic
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acidic
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acidic
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acidic
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Example reactions
4Na(s) + O2(g) ----> 2Na2O(s)
P4(s) + 5O2(g) -----> P4O10(s)
2S(s) + Cl2(g) ----->S2Cl2(l)
2Na(s) + 2H2O(l) -----> 2NaOH(aq) + H2(g)
NaCl(s) + (aq) -----> Na+(aq) + Cl-(aq)
AlCl3(s) + 6H2O(l) -----> Al(H2O)5(OH)2+(aq)
+ H+ + 3Cl-(aq)
Task 4.2a(i) write equations for oxygen reacting with Mg,
Al, Si, and S.
Write equations for chlorine reacting with Na, Mg, Al, Si and P.
Write equations for water reacting with Mg and Cl2.
4.2a(ii) Formulae and acid-base character of oxides and hydroxides
A basic substance reacts with an acid to form a salt.
An amphoteric compound will react with an acid or a base.
| Substance | acid-base nature |
| Na2O NaOH | Strongly basic |
| MgO Mg(OH)2 | Strongly basic |
| Al2O3 Al(OH)3 | amphoteric |
| Si02 | acidic |
| P4O10 | acidic |
| SO2 SO3 | Strongly acidic |
| Cl2O | Strongly acidic |
Base behaviour
NaOH(aq) + HCl(aq) ---> NaCl(aq) + H2O(l)
MgO(aq) + 2HCl(aq) ---> MgCl2(aq) + H2O(l)
amphoteric behaviour
Al2O3 + 6HCl(aq) ---> 2AlCl3 + 3H2O(l)
base acid
Al2O3 + 2NaOH(aq) +3H2O(l) ---> 2NaAl(OH)4(aq)
sodium aluminate
acid base [Al(OH)4(H2O)2]-
Acid behaviour
SiO2 + 2NaOH(aq) ---> Na2SiO3(aq)
+ H2O
P4O10 + 12NaOH ---> 4Na3PO4 + 6H2O
Task 4.2a(ii) Write equations to show acid base behaviour
of Na2O, Mg(OH)2 , Al(OH)3 , SO2
, SO3 and Cl2O (product with NaOH NaClO2 and
NaClO3)
4.2a(iii) Formulae of chlorides and reactions with water
| Chloride | Reaction with water |
| NaCl | NaCl(s) + aq ---> Na+(aq) + Cl-(aq) dissolves to form neutral solution |
| MgCl2 | MgCl2 + aq ---> Mg2+(aq) + 2Cl-(aq)
dissolves to form slightly acidic solution On heating hydrated chloride is hydrolysed MgCl2 + H2O ---> Mg(OH)Cl + HCl |
| AlCl3 | AlCl3 + 6H2O(l) ---> [Al(H2O)6]3+(aq)
+ 3Cl-(aq) acidic solution due to [Al(H2O)6]3+(aq) ---> [Al(OH)(H2O)5]2+(aq) + H+(aq) |
| SiCl4 | SiCl4 + 2H2O ---> SiO2 + 4HCl |
| PCl3 | PCl3 + 3H2O ---> H3PO3 + 3HCl |
| PCl5 | PCl5 + H2O --cold->POCl3 + 2HCl , H3PO4 formed when hot |
| S2Cl2 | 2S2Cl2 + 2H2O ---> SO2 + 3S + 4HCl |
| Cl2 | Cl2 + H2O ---> HOCl + HCl |
Task 4.2a(iii)
Write an equation for the hydrolysis of the magnesiumhexahydrate(II) ion.
Write an equation to show the formation of H3PO4.
Describe what would be seen in each of the reactions of chlorides above.
4.2a(iv) Reactions structure and bonding in oxides and chlorides
| Substance | Structure | Bonding | Relevant Property Explained |
| Na2O | giant ionic | ionic | basic as O2- ion pulls H+ from water to leave OH- |
| MgO | giant ionic | ionic | basic as above |
| Al2O3 | giant ionic | ionic some covalent character | amphoteric |
| SiO2 | giant molecular | covalent | acidic insoluble |
| P4O10 | simple molecular | covalent | acidic |
| SO2 and SO3 | simple molecular | covalent | acidic, S accepts lone pair from oxygen in water. |
| Cl2O | simple molecular | covalent | acidic |
| NaCl | giant ionic | ionic | neutral solution |
| MgCl2 | giant ionic | ionic | hydrolysis on heating of hydrated salt |
| AlCl3 SiCl4 PCl3 PCl5 | simple molecular | covalent | hydrolysis |
Task 4.2a(iv).1
Draw dot and cross diagrams for one covalent and one ionic example above.
Draw one example for each type of structure mentioned above.
Atoms become more electronegative from left to right across the period.
Na and Mg are electropositive so lose electrons in reactions and form positive
ions. Their atoms force oxygen atoms to form oxide ions O2-.
Oxide ions are strong bases because they can accept protons from water (or
donate electron pairs to hydrogen atoms in water).
O2- + H2O ---> 2OH-
O2- + H+ ---> OH-
Al is not so electropositive and Al2O3 has some covalent
character. O2- ions are not well formed and Al2O3
is only just able to accept protons from an acid (or donate a pair of electrons
from oxygen to a hydrogen atom).
Al2O3 + 6H+ ---> 2Al3+ + 3H2O
Si, P, S and Cl are increasingly electronegative. They cannot form oxide
ions from oxygen at all. The atoms of these elements in their oxides are however able to
accept pairs of electrons from oxygen in water (so behave as acids).
SO3 +H2O ---> H2SO4
Task 4.2a(iv).2 Draw diagrams to show pairs of electrons moving to start
above reactions.
Task 4.2a(iv).3 Period
3 quiz
4.2b(i) Metallic character in group 4
Metallic character increases down group 4 as the atomic number increases.
4.2b(i) Story
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gcm-3 |
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electronic structure | IE/ kJmol-1 |
Ë(X-X) kJ/mol-1 |
Character |
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1086 | 348 |
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789 | 176 |
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Ge |
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762 | 188 |
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(Kr)4d10 5s25p2 |
709 | 150 |
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(Xe)4f145d10 6s26p2 |
716 | - |
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Complete the electronic structures above. What is
the trend in metallic character as the atomic number increases in group 4?
Explain the changes in properties down the group in terms of structure and
bonding.
Metals lose outer electrons.
At the bottom of group 4, in tin and lead, outer electrons are far
from the nucleus, weakly held and so lost easily. These outer
electrons are also more shielded than in smaller atoms. Tin and lead therefore
easily lose electrons, form ions and are metals. Their outer electrons delocalise to
give the pure element a metal structure.
At the top of group 4, in carbon and silicon, outer electrons are close
to the nucleus and strongly held so not easily lost. Carbon and silicon
are therefore non-metals.
Atomic radius increases down the group
Small atoms at the top attract bonding pairs of electrons strongly
so covalent bonds favoured.
Ionisation energies high at top because electrons close to nucleus
so no positive ions formed.
Large atoms at bottom weakly attract bonding pairs of electrons so covalent
bonds are formed with difficulty.
Ionisation energies low at bottom because electrons distant from nucleus
so positive ions form.
p electrons likely to be released, form a 'sea' near bottom of the
group as they are progressively better shielded than s electrons
towards the bottom
of the group (inert pair effect).
Acid Base character
Although CO is neutral CO2 is an acidic oxide, dissolving
in water to form the weak acid carbonic acid.
CO2 + H2O -----> H2CO3
CO2 + OH- ---> HCO3-
CO2 +2OH- ---> CO32- +H2O
Silicon (IV) oxide is an acidic oxide which reacts with concentrated
alkalis to form silicates.
SiO2(s) + 2OH-(aq) -----> SiO32-(aq)
+ H2O(l)
GeO and GeO2 are both amphoteric
Lead (II) and lead (IV)oxide are amphoteric. It reacts with acid to
form lead(II) salts
PbO(s) + 2HCl(aq) -----> PbCl2(aq) + H2O(l)
PbO2(s) + 4HCl(aq) -----> PbCl4(l) + 2H2O(l)
below 20oC
They react with alkalis to form a plumbate(II) (plumbite) or plumbate(IV).
PbO(s) + 2OH-(aq) +H2O(l) -----> [Pb(OH)4]2-(aq)
PbO2(s) + 2OH-(aq) + 2H2O(l) ----->
[Pb(OH)6]2-(aq)
Write equations which show sodium hydroxide reacting with
carbon dioxide, silicon dioxide lead II oxide and lead IV oxide.
Write equations to show sulfuric acid reacting with lead II oxide and lead IV
oxide.
Write equations to show that GeO is amphoteic.
4.2b(ii) +2 oxidation state in group 4
The +4 state is stable at the top of the group, but as we go down the group (i.e. as the atomic number increases), the +2 oxidation state becomes more stable whilst the +4 state becomes less stable. 4 electrons (+4 oxidation state) may be available for bonding in group 4. An s electron is promoted to a p orbitals for this oxidation state. The energy for this promotion is available from forming 4 covalent bonds (if strong enough). Covalent bond strength drops down the group so at the bottom a valency of only two is favoured. In big atoms like lead the inner pair of s-electrons are not involved in bonding. The outer pair of p electrons experience more shielding and are more easily lost. In small atoms like carbon all four electrons experience a similar amount of shielding. This results in all 4 electrons being involved in bonding.
The +2 oxidation state of tin is reducing e.g.
Sn2+(aq) + Hg2+(aq) --->
Sn4+(aq) + Hg (l).
The +4 oxidation state of lead is oxidising e.g. with conc. HCl
PbO2(s) + 4HCl(aq) ---> PbCl2(s)
+ 2H2O(l) + Cl2(g)
Task 4.2b(ii) What evidence is there that the +4 oxidation
state for Sn is more stable than the +2 state?
Draw a labelled diagram to illustrate the inert pair effect.
What would be seen if lead IV oxide is added to conc HCl?
4.2b(iii) The structure of carbon tetrachloride
Carbon tetrachloride or tetrachloromethane has a molecular structure. The
molecules have a tetrahedral shape as the central carbon atom is surrounded by 4
bonding pairs of electrons.
Task
4.2b(iii) Draw SiCl4.
4.2b(iv) The behaviour of carbon
tetrachloride and silicon tetrachloride
with water
Carbon tetrachloride does not react with water. The bonding electrons used
by carbon are from 2s and 2p orbitals. The carbon atom has no available
orbitals (3s are too energetically far away and there are no 2d orbitals) to
hold lone pairs of electrons from oxygen atoms on water molecules. Silicon
tetrachloride undergoes a vigorous hydrolysis reaction in which steamy fumes of
HCl form.
SiCl4(l) + 2H2O ---> SiO2(s) + 4HCl(g)
In silicon tetrachloride the bonding electrons used by silicon are from 3s and
3p orbitals. Silicon has 3d orbitals available which are energetically
close to the 3p orbitals. These 3d orbitals accept lone pairs of electrons
from oxygen atoms in water molecules and start to form bonds.
Task 4.2b(iv) Draw electronic structures for carbon and
silicon.
What would you see in the hydrolysis of silicon tetrachloride?