This document discusses the comparative chemistry of main group elements. It covers topics such as metallic character, oxidation states, electronegativity, the inert pair effect, and allotropes of various main group elements. Allotropes refer to different structural forms of the same element that have distinct physical properties but similar chemical properties. The document provides examples of allotropes for elements in groups 13 through 16, such as different crystalline forms of boron and carbon buckminsterfullerene.

1. Comparative Chemistry of Main Group Elements
The main group is the group of elements (sometimes called
the representative elements) whose lightest members are
represented by helium, lithium, beryllium, boron, carbon,
nitrogen, oxygen, and fluorine as arranged in the periodic
table of the elements. The main group includes the elements
(except hydrogen, which is sometimes not included) in groups
1 and 2 (s-block), and groups 13 to 18 (p-block).

3. Metallic character refers to the level of reactivity of a metal. Metals tend to lose
electrons in chemical reactions, as indicated by their low ionization energies. Within
a compound, metal atoms have relatively low attraction for electrons, as indicated
by their low electronegativities.
The metallic character increases as you go down a group. Nonmetals tend to gain
electrons in chemical reactions and have a high attraction for electrons within a
compound.

4. Oxidation State of an element is defined as the residual charge left on
the central atom, when other atoms of the compound are removed in
their usual oxidation state.

5. Inert Pair Effect
Electronegativity is a measure of an atom's ability to attract shared electrons to
itself. On the periodic table, electronegativity generally increases as you move
from left to right across a period and decreases as you move down a group.
Electronegativity

6. Anomalous Behaviour of Second Period Elements
The first period has only two elements – hydrogen and helium .The second period
has eight elements- lithium ,beryllium, boron, carbon ,nitrogen ,oxygen ,fluorine
and neon.These elements are remarkably different in their behaviour as compared
To the other elements present in the same group.

10. Allotropy
Its defined as the phenomenon in which an elements exists
in different physical forms having different physical
properties but similar chemical properties.

11. Enantiotropy
When two allotropic forms of elements exist at one particular temperature ,they
Known as enantiotropes and temperature is known as transition temperature.
Monotropy
When one of the cyrstalline allotropic form of elements is stable below its
melting point of elements and other is unstable .
Dynamic Allotropy
In dynamic allotropy ,two allotropic forms of an elements exist in
equilibrium state at a particular temperature and in the same physical state.

12. Boron (B), the second hardest element, is the only allotropic element in Group 13.
It is second only to carbon (C) in its ability to form element bonded networks. Thus,
in addition to amorphous boron, several different allotropes of boron are known,
of which three are well characterized. These are red crystalline α -rhombohedral
boron, black crystalline β -rhombohedral boron (the most thermodynamically
stable allotrope), and black crystalline β -tetragonal boron. All are polymeric and
are based on various modes of condensation of the B 12 icosahedron.
Allotropes of Group 13 Elements

13. Allotropes of Group 14 Elements

14. Buckminsterfullerene is a type of fullerene with the formula C60. It has a
cage-like fused-ring structure (truncated icosahedron) that resembles a
soccer ball, made of twenty hexagons and twelve pentagons. Each carbon
atom has three bonds. It is a black solid that dissolves in hydrocarbon
solvents to give a violet solutions

16. Allotropes of Group 15 Elements
There are two allotropic elements in Group 15, phosphorus and arsenic . Phosphorus
exists in several allotropic forms. The main ones (and those from which the others are
derived) are white, red, and black (the thermodynamically stable form at room
temperature)

17. Allotropes of Group 16 Elements