what is mole concept?what is avogadro's constant?what is its use?

The mole is the amount of a substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon-12; its symbol is "mol." When the mole is used, the elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles.

 One mole is an amount of substance containing Avogadro's number of particles. Avogadro's number is equal to 602,214,199,000,000,000,000,000 or more simply, 6.02214199 × 10²³.

as we have 12 nos. inone dozen same way mole is the unit used to measure atoms and molecules in chemistry . reason they are so tiny that they cannot be counted in 10 or 100 or 1000 so it is counted in mole unit

arbitarily scientist have taken wt of carbon-12 isotope as 12 amu and it is said to contain one mole of carbon meaning 12 gm of carbon contains 1 mole of carbon and as 1 mole is equal to 6.023 x 10²³ atoms of carbon.

feel free for any such query in this topic. hope this wil help u out

The Mole Concept (Avogadro's Number)

Molecules and atoms are extremely small objects - both in size and mass. Consequently, working with them in the laboratory requires a large collection of them. How large does this collection need to be? A standard needs to be introduced. This standard is the "mole". The mole is based upon the carbon-12 isotope. We ask the following question: How many carbon-12 atoms are needed to have a mass of exactly 12 g. That number is NA - Avogadro's number. Thus, NA is defined by 



 

 

A convenient name is given when there is an Avogadro's number of objects - it is called a "mole". Thus in the above example there was a mole of pennies.

The mole concept is no more complicated than the more familiar concept of a dozen : 1 dozen = 12 objects. From the penny example above one might suspect that the mass of a mole of objects is huge. Well, that is true if we're considering a mole of pennies, however a mole of atoms or molecules is a different story. Recall that the atomic mass unit (amu) is defined as 1/12 the mass of a carbon-12 atom. Consequently we have the relation 

Thus, a mole of carbon-12 atoms has a mass of just 12 g. What about other atoms? In the periodic table the atomic mass of the elements is given. For example the atomic mass of magnesium is 24.305 amu. This is the average isotopic mass of naturally occurring magnesium. What is the molar mass of magnesium in grams? From the equation above we get 1 amu = 1g/NA or 1 amu = 1.66054x10^-24 g. Thus, a mole of magnesium atoms has a mass of NA x 24.305 amu x (1.66054x10^-24 g/amu) = 24.305 g. A mole of magnesium atoms has a mass of 24.305 g. This example demonstrates that the atomic mass of magnesium can be interpreted in one of two ways: (1) the average mass of a single magnesium atom is 24.305 amu or (2) the average mass of a mole of magnesium atoms is 24.305 g;

 A similar conclusion follows for all of the other elements.

also check

http://en.wikipedia.org/wiki/Avogadro's_number