a) Describe and explain the variation of physical and chemical properties of group 14
elements and their compounds
The carbon family, (Group 14) in the p-block, contains carbon (C), silicon (Si), germanium (Ge),
tin (Sn)and lead (Pb). Each of these elements has only two electrons in its outermost p orbital
each. The Group 14 elements tend to adopt oxidation states of +4 and, for the heavier elements,
+2 due to the inert pair effect.
Members of this group conform well to general periodic trends. Atomic radii increase down the
group, and ionization energies decrease. Metallic properties increase down the group. Carbon is a
non-metal, silicon and germanium are metalloids, and tin and lead are poor metals (they conduct
heat and electricity less effectively than other metals such as copper). Despite their adherence to
periodic trends, the properties of the carbon family vary greatly in both physical and chemical
properties such as density, melting point and boiling point, electrical conductivity thus for
physical properties and for chemical properties includes their reactivities
Melting and boiling points of group 14
Melting Points and Boiling Points
The melting points and boiling points of group 14 elements decrease as we go down the group,
thus due to
the change from covalent to metallic bonding. Carbon and silicon have strong covalent bond
which results in formation of giant molecular structures which requires a lot of energy to break,
hence higher melting points. The trend ultimately shows that as the atoms get bigger and bonds
get longer, the bonds get weaker
Brittleness
Carbon as diamond is very hard, but if hit with a hammer it can easily shatter
In other words, there is near no flexibility in the carbon bonds of diamond silicon, germanium,
and grey tin (form of tin existing in a covalent structure) are also very brittle. White tin and lead
have metallic structures, and thus the atoms can roll over each other without disrupting the
metallic bonds, thus they are malleable and ductile, properties of metals
Electrical conductivity
In diamond form has no electrical conductivity, since the electrons are too tightly bound to move
freely graphite is more of an anomaly than an antithesis, due to the unique structure of graphite
which can slide over each other hence it has free electrons which can conduct electricity. Silicon,
germanium, and grey tin are semiconductors can conduct electricity if enough energy is passed
through. When lots of atoms come together to form a large structure, their atomic orbitals merge
thus producing a large number of molecular orbitals. These orbitals arrange in bands of
increasing energy in terms of reference, one band is known as a valence band
- Hold the electrons which make the normal covalent or metallic bonding
- And the other the Conductance Band
- A higher energy level band
- As temperature increases, electrons gain thermal energy, and some electrons may jump from
the valence band into the conductance band if the distance is small enough
- Once the electrons reach the conductance band, they are delocalized and can freely move to
conduct electricity
Diamond
- The energy gap between the valence band and the conductance band is too high for such a jump
to occur
Silicon
- In silicon, and the same for Germanium and Grey Tin the band gap is small enough for
electrons to jump, and thus silicon is a semiconductor
White Tin and Lead
- They act as normal metallic conductors of electricity as described by the properties of metallic
bonds found here
The Trend
- Thus, the trend of the non-metallic non-conductance behaviour of Carbon to the conductance
behaviour of white tin and lead can be clearly seen throughout the Group 4 elements
Chemical properties
The reactivity of elements decreases down the group. The inert pair effect becomes the
reactivity of elements decreases down the group. The inert pair effect becomes increasingly
effective down the group. The stability of the +4oxidation state decreases increasingly effective
down the group. The stability of the +4 oxidation state decreases. BRIGGS 5thedition
while that of the +2 oxidation state increases on descending the group, while that of the +2
oxidation state increases on descending the group .E .g Sn2+ exist as simple ion and is strongly
reducing , Sn4+ is covalent ,Pb2+ is ionic ,stable and more common than Pb4+ .
Reaction with water
C, Si and Ge are unaffected by water, Sn reacts with steam to give SnO, C, Si and Ge are
unaffected by water. Sn reacts with steam to give SnO and H and H . Pb is unaffected by water
due to the formation of protective oxide layer at the surface.
Reaction with acids
C, Si and Ge are not affected by dilute acids. Sn and Pb reacts with dilute nitric acid .C, Si and
Ge are not affected by dilute acids, Sn and Pb reacts with dilute nitric. Application in chemistry
Birk, James 1989.The oxides of group 14, some of them can act as acids when mixed with alkali
4Sn + 10HNO3
4Sn(NO3)2 + NH4NO3 + 3H2O
3Pb + 8HNO3
3Pb(NO3)2 + 2NO +4H2O
Reaction of group 14 oxides with acid
XO2 + 2NaOH
Na2XO3 + H2O
Thus for Ge, Sn and Pb for all reactions, hot and concentrated sodium hydroxide is used
Reaction with alkalis
C is not affected by alkalis. C is not affected by alkalis. Si reacts with alkalis forming silicates.
Si reacts with alkalis forming silicates.
Sn and Pb also react with alkalis forming stannate, [Sn(OH)6] ,and plumbate ,
[Pb(OH)6]2-.These reactions show that Sn and Pb are amphoteric. These reactions show that Sn
and Pb are amphoteric.
Reactions with halogens
Graphite but not diamond is affected by F2 at higher temperatures giving (CF)n
Si and Ge react with all halogens, forming volatile SiX4 and GeX4.
Sn and Pb are less reactive but do react giving SnX4 and PbX2.
Sn + 2X2
Pb + Cl2
SnX4
PbCl2
b) Relationships in the periodic table are similarities between pairs of elements in different
groups and periods. By reference to the first three elements of the second period9Li,Be and
B),their physical properties and relevant balanced chemical equations ,describe the similarities .
Li and Mg form only normal oxides whereas Na forms peroxide and metal below Na in addition
form super oxides. Li is the only group 1 element which forms a stable nitride, Li3N and Mg as
well as other group 2 elements also form nitrides
6Lis+N2g
3Mgs+N2s
2Li3NS
Mg3N2s
Li and Mg can form stable nitride.
They can also form stable oxides thus
4Li + O2
2Mg + O2
2Li2O
2MgO
Lithium Carbonate is sparingly insoluble in water and group 2 elements also dissolve
Li2CO3
MgCO3
Li2O + CO2
MgO + CO2
Both Li and Mg form covalent organo-metallic compounds. LiMe and MgMe2 are both valuable
synthetic reagents .Both Li and Mg chlorides are deliquescent(absorb moisture from
surroundings) and soluble in alcohol and pyridine .LiCl ,like (MgCl.6H2O) separate from
hydrated crystal LiCl.2H2O.Thus the chemistry of Li has similarities to those of Mg . Reaction of
group 2 Clark, Jim (2005) and Inorganic chemistry Shrive, Duward (2006)
B2O3 is an acidic oxide, like SiO2
B2O3 + 6NaOH
SiO2 + 2NaOH
2Na3BO3+ H2O
Na2SiO3 + H2O
Boron shows anomalous behaviour in its group because of its small size and non-availability of d
orbitals .It resembles silicon ,the second member of the next higher group .Both B and Si are
non-metals and exist in allotropic forms .They have high melting points and are semi- conductors
.The other members of group 13 are metals .
Both boron and silicon form halides which are readily hydrolysed
BCl3 + 3H2O
B(OH)3 +3HCl
Boric acid
SiCl4 + 4H2O
Si(OH)4 + 4HCl
Silic acid
Both boron and silicon form several volatile and spontaneously inflammable hydrides called
boranes and silanes ,respectively .The hydrides are readily hydrolysed .The lower hydrides can
be obtained by the reduction of chlorine with LiAlH4
4BCl3+ 3LiAlH4
SiCl4 + LiAlH4
3AlCl3 + 3LiCl + 2B2H6
AlCl3 + LiCl + SiH4
Be and Al also has some similarities .They all have the tendency to form covalent compounds e
.g chlorides of both being covalent are soluble in organic solvents .Both BeCl2 and AlCl3 act as a
Lewis acids are used as Friedel-Crafts catalyst .Inorganic chemistry Shrive ,Duward 2006.Both
Be and Cl are resistant to the acid action due to formation of protective film of the oxides on
their surface
The oxides of both beryllium (BeO) and Aluminium(Al2O3) are hard and have high melting
solids .They are also amphoteric and dissolve in NaOH solution as well e .g for HCl
Be0 + 2HCl
BeCl2 + H2O
Be0 + 2NaOH
Na2BeO2 + H2O
Al2O3 + 6HCl
2AlCl3 + 3H2O
Al2O3 + 2NaOH
2NaAlO2 + H2O
References
Briggs 5th edi