Mole Concept
Banks have an extremely large number of coins of various denominations. Counting of such a large number of coins is a difficult job. So, in banks, they weigh coins, rather than count them. The bank people know that a fixed number of a particular coin will always have the same mass. This means that from the mass of a particular type of coins, they can find the number of coins. Thus bank people link the mass of coins to the number of coins present. In chemistry also, scientists link the mass of an element or compound to the number of atoms or molecules present in them. This is done through the 'mole'.
Scientists count atoms and molecules by weighing them. It has been found by performing experiments that if we weigh an element equal to its atomic mass in grams, then it contains atoms of the element. Now, the gram atomic mass of the element as well as atoms of the element, both represent 1 mole of element.Similarly, if we weigh a compound equal to its molecular mass in grams, then it contains molecules of the compound. In this case also, the gram molecular mass as well as molecules represent 1 mole of the compound.Thus, mole is a link between the mass of atoms (or molecules) and the number of atoms (or molecules).
The gram atomic mass of carbon element is 12 grams. Now, when a scientist is performing an experiment by weighing 12 grams of carbon, he knows that he is dealing with atoms of carbon. In other words, he is working with 1 mole of carbon. The gram molecular mass of water is 18 grams. So, when a scientist is using 18 grams of water in his experiment, he knows that he is carrying out the reaction by using molecules of water. In other words, the scientist is working with 1 mole of water. In the following discussion, we will start by considering mole as a .collection of particles (atoms,molecules or ions) of a substance. We will give the proper definition of mole after a while.
A group of particles (atoms, molecules or ions) of a substance is called a mole of that substance.
Thus, 1 mole of atoms = atoms
And, 1 mole of molecules = molecules
It is obvious that we can have a mole of atoms or a mole of molecules of a substance. For example,oxygen atom is O and oxygen molecule is O2. So, we can have a mole of oxygen atoms or a mole of oxygen molecules.
1 mole of oxygen atoms (O) = oxygen atoms
And, 1 mole of oxygen molecules () = oxygen molecules
Thus, mole represents a definite number of particles, atoms or molecules, of a substance. This number of , which represents a mole, is known as Avogadro number (L). We can now say that a mole represents an Avogadro number of particles of a substance. In addition to the definite number of particles of a substance, the mole also represents a definite amount (or mass) of a substance. This point will become more clear from the following discussion.
Notes
Atoms and Molecules - Notes
2. Monovalent Cations (Cations Having a Valency of 1+)
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3. Divalent Cations (Cations Having a Valency of 2+)
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5. Trivalent Cations (Cations Having a Valency of 3+)
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6. Formulae of Some Molecular Compounds
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8. Molecular Formulae of Some Common Elements
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9. an example, let us give the significance of symbol C
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11. As an example, let us give the significance of the formula H
2O
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13. 2. A Negatively Charged Ion is Known as Anion
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16. Explanation of the Law of Conservation of Mass
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23. 1. A Positively Charged Ion is Known as Cation
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26. Simple Ions and Compound Ions (Polyatomic Ions)
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27. Gram Atomic Mass And Gram Molecular Mass
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31. Explanation of the Law of Constant Proportions
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34. Significance of the Formula of a Substance
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36. Molecular Masses of Some Common Elements
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42. Problems Based On Moles Of Molecules
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43. Divalent Anions (Anions Having a Valency of 2-)
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44. Experiment to Verify Law of Conservation of Mass
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46. Writing Of Formulae Of Ionic Compounds
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