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By :
Yesenia, jose, & Jorge
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Carbon is found free in nature in three allotropic forms: amorphous, graphite, and
diamond. Graphite is one of the softest known materials while diamond is one of
the hardest.
Silicon makes up 25.7% of the earth's crust by weight, and is the second most
abundant element, exceeded only by oxygen. It is found largely as silicon oxides
such as sand (silica), quartz, rock crystal, amethyst, agate, flint, jasper and opal.
Silicon is found also in minerals such as asbestos, feldspar, clay and mica.
Germanium is a gray-white semi-metal, and in its pure state is crystalline and
brittle, retaining its lustre in air at room temperature. It is a very important
semiconductor material. Zone-refining techniques have led to production of
crystalline germanium for semiconductor use with an impurity of only one part in
10-10.
Tin is a silvery-white metal, is malleable, somewhat ductile, and has a highly
crystalline structure. Due to the breaking of these crystals, a "tin cry" is heard when
a bar is bent. The element has two allotropic forms. On warming, grey, or α-tin,
with a cubic structure, changes at 13.2°C into white, or β-tin, the ordinary form of
the metal. White tin has a tetragonal structure. When tin is cooled below 13.2°C, it
changes slowly from white to grey.
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Lead is a bluish-white lustrous metal. It is very soft, highly
malleable, ductile, and a relatively poor conductor of electricity. It
is very resistant to corrosion but tarnishes upon exposure to air.
Holmium is relatively soft and malleable, and is stable in dry air
at room temperature. It oxidises rapidly in moist air and at
elevated temperatures. The metal has unusual magnetic
properties. The metal is a rare earth metal found in monazite,
gadolinite and other minerals.
Einsteinium is radioactive rare earth metal named after Albert
Einstein. It is of no commercial importance and only a few of its
compounds are known
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The carbon family consist of carbon, silicon, germanium, tin, lead,
holmium & einsteinium.
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The ability of an atom in a molecule to attract a shared electron pair to itself, forming a
polar covalent bond.
The electronegativity generally increases as you go from left to right across the periodic
table. It decreases as you go down the periodic table.
The horizontal comparison. As you go across a period from left to right, the atoms of each
element all have the same number of energy levels and the same number of shielding
electrons. The factor that predominates is the increased nuclear charge. When the nuclear
charge increases, so will the attraction that the atom has for electrons in its outermost
energy level and that means the electro negativity will increase.
when you go from one atom to another down a group, you are adding one more energy
level of electrons for each period. The increased shielding nearly balances the increased
nuclear charge and the predominant factor is the number of energy levels that are used by
the electrons. So as you go from fluorine to chlorine to bromine and so on down the
periodic table, the electrons are further away from the nucleus and better shielded from
the nuclear charge and not as attracted to the nucleus. For that reason the electronegativity
decreases as you go down the periodic table.
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These elements have only two electrons in the outermost p orbital. That is, their valence
electron configuration is ns2np2. They tend to have 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. The atomic radii
increase as you move down the group, and ionization energies decrease. Metallic
properties increase as you move down the group. Carbon is a non-metal; silicon and
germanium are metalloids; and tin and lead are poor metals
Despite their adherence to periodic trends, the properties of the Carbon family vary
greatly. Carbon is a non-metal. Tin and Lead behave entirely as metals. In their
elemental solid state, Group 14 metalloids, silicon and germanium, act as electrical
semiconductors, although silicon is mainly non-metallic.
With 4 valence shell electrons, elements of the carbon family tend to form covalent
compounds. With increasing mass and atomic radius these elements become
increasingly metallic and have lower melting and boiling points. Group 14 elements
form gaseous hydrogen compounds with difficulty. These are either unstable or
combustible. All but lead form oxides, sulfides, and halides in the +4 oxidation state. The
+4 oxidation state predominates in carbon, silicon, and germanium; the +2 and +4
oxidation states both appear in tin, and the +2 oxidation state prevails in lead. Halides in
the +4 state form for all of these elements, and they are covalent.
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Both atomic radii and atomic volume increases gradually on moving down the group due to
the effect of extra shell being added from member to member.
C
Si
Ge
Sn
Pb
Atomic radius (pm)
0.77 111 122
141
144
Atomic volume (ml)
3.4 11.4 13.6
16.3
18.27
Some of the ionic radii involving six co-ordination of these group elements are given
below,
C
Si
Ge
Sn
Pb
Ionic radius (M2+) in pm –
–
73
118
119
Ionic radius (M++) in pm –
40
53
69
78