Some important definations of class X chemistry chapter carbon and its compunds

1. The earth's crust has only 0.02%carbon in the form of minerals like carbonates,bicarbonates,coal,and petroleum
2. The atmosphere has 0.03% of carbon dioxide
3. Inspite of its small amount available in nature carbon is a versatile  element as it forms the basis for all living organisms and many thing which we use
4.bonding in carbon:
(A) atomic number of carbon =6
(B)electronic configuration has 2electrons in k shell and four electrons in L shell
(C) in order to attain the Nobel gas configuration carbon should either gain 4 electrons or lose 4 electrons or can share it's 4 electrons with some other element
(D) gain of 4 electrons (to form octet ,i.e,8 electrons in c4- anion is difficult because then a nucleus with 6 protons will have to hold extra four electrons.
(E) loss of 4 electrons (to attain duplet,i.e, 2electrons like he atom in c4+ cation) is difficult as it requires large amount of energy to remove four electrons
(f) carbon ,hence,overcomes this difficulty by sharing it's four valency electrons with other atoms of carbon or with atoms of other elements
These electrons contributed by the atoms for mutual sharing in order to acquire the stable Nobel gas configuration is called covalency of that atom
Hence,carbon shows tetracovalency
(G) the simplest molecule formed by sharing of electrons can be represented by electron dot structure
5. Allotropes of carbon the phenomenon by means of which an element can exist in two or more forms with similar chemical properties but different physical
Properties is called allotropy and the different forms are called allotropes carbon shows three allotropic forms:
1. Diamond
2. Graphite
3. Fullerenes
6. Fullerness- A new category of carbon allotrope fullerness are spherical in shape or a soccer ball like
The first fullereness  identified was c- 60 with 60 carbon atoms arranged like geodesic dome designed by US architect, Buckminster fuller hence these are also known as Buckminster fullernes or bucky ball structures.
7. Cause of versatile nature of carbon: four main reasons for versatile nature of carbon are :
(A) catenation-- it is the unique property of self linkage of carbon atoms by means of covalent bonds to forms straight chains ,or branched chains or the rings different sizes
(B) tetravalency-- due to small size and presence of four valency electrons carbon can form strong bonds with other carbon atoms ,hydrogen, oxygen,nitrogen,or sulpher,etc for example compounds of carbon with hydrogen are called hydrocarbons

(C)isomerism: the phenomenon by mean of which the carbon compounds with same molecular formulae show different structures, and properties