Wed January 26, 2011 By: Nikhil Mathew

What Is Actually Mole Concept?

Expert Reply
Wed January 26, 2011
Dear Student
In chemistry the mole is a fundamental unit in the Système International d'Unités, the SI system, and it is used to measure the amount of substance. This quantity is sometimes referred to as the chemical amount. 
So, a mole is the quantity of an element that you have when you weigh out in grams the amount of that element specified by the atomic weight.
The special property of a mole is that one mole of an element contains the same number of atoms as one mole of any other element, even though at this moment we don't know what number of atoms that happens to be.

Moles of Compounds

The concept of a mole can be applied to compounds as well as elements. A mole of a compound is what you have when you weigh out, in grams, the formula weight of that compound. (Use the molecular weight if the compound is a molecular material.) For example, the formula weight for HF is 20.0. That means that one mole of HF weighs 20.0 grams, and you can use that relationship to convert back and forth between grams and moles.

Moles of Molecular Elements

Special care must be taken when dealing with moles of a molecular element. If someone talks about "so many moles of hydrogen," it is necessary to find out whether they mean moles of atomic hydrogen (H, 1.0 g/mole) or moles of molecular hydrogen (H2, 2.0 g/mole). To avoid mistakes, look for a formula or consider the context.


2. Filling of electrons
Always remember that the shell with lower energy will be filled first.

An atom's electron shells are filled according to the following theoretical constraints:

  • Each s subshell holds at most 2 electrons
  • Each p subshell holds at most 6 electrons
  • Each d subshell holds at most 10 electrons
  • Each f subshell holds at most 14 electrons.
We hope that clarifies your query.
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