How do you feel the number **6.022 x 10 ^{23}**.In first look it seems a mere, small and simple number. But on expanding this number will show its gigantism.Have you ever tried to expand such a number.Now for your convenience I had done it here. Its expanded form is 602200000000000000000000.What a huge digit is this ? Yes, that is the number I am talking with.The above number is called

**Avogadro's Number**. This number has some relation with what is called

**mole**in chemistry, one of the branches of science.It is a counting unit used in Chemistry.

Let us have a close look to this number. When there is two shoes we say a pair of shoes. If there is 12 pencils we say a dozen pencil.Like that if there is 6.022 x 10 ^{23} pencils we can say a mole of pencils.Understood?

It is easy to say .But can you imagine its size? How many days will you take to count it? Ten, twenty , thirty or hundred ?If any one of this is your answer you are absolutely wrong. Your lifetime will not be enough to count completely this much! Will two times your life be enough to count ? No. Ten times your lifetime may not be enough to complete the counting of Avogadro's number!!!If you are able to count 1 crore pencils within a second (impossible to a man) you can complete counting of one mole pencils just in 200 crore years !!!!!Then how is the size of this number ? Incredible !!!

Now we can look the chemistry of this number. From above description it is clear that 1 mole of atoms = 6.022 x 10 ^{23} atoms or 1 mole of water molecule = 6.022 x 10 ^{23} water molecules

What is the peculiarity of mole then? Let us have a look. We know that the atomic mass of hydrogen is 1.Let us weigh hydrogen equal to its atomic mass. That is 1 gram of hydrogen is taken. Then it will contain 6.022 x 10 ^{23} hydrogen atoms ! Similarly the atomic mass of oxygen is 16.If we take 16 grams of oxygen it will contain 6.022 x 10 ^{23} oxygen atoms. The molecular mass of water is 18. So if we take 18 grams of water it will contain 6.022 x 10 ^{23} water molecules!!(To get atomic masses of other elements please refer the periodic table of elements)

In short if we weigh any substance equal to its atomic mass in gram it will contain one mole atoms of that substance. If we weigh any substance equal to its molecular mass in gram it will contain one mole molecules of that substance.

It does not end here. According to **Avogadro's law** a gas at a pressure of 1 atmosphere and temperature of zero degree Celsius which is contained in a volume of 22.4 liters will have one mole of that gas. In another words if you require one mole of oxygen take it in a container of volume 22.4 liters at a temperature of zero degree Celsius and 1 atmospheric pressure.

Since atoms and molecules are so small that naked eyes can't see it is impossible to count them as well. But the above given result is experimentally proved. Thus mole is used to count the atoms or molecules without actually counting. It is used for various types of calculations in chemistry.

**October 23 ^{rd}** was celebrated as

**mole day**. What is that days relation with mole ? Just have a close look at Avogadro number. It is 6.022 x10

^{23}. October is the tenth month which is the multiple here. It is raised to the power 23 which is chosen as the date. Not enough, the mole day celebration is from 6.022 AM to 6.022 PM !!! The day is celebrated by

**National Mole Day Foundation**. In India we do not hear the news of celebration of this day. But the chemists and chemical students of countries like Sweden , Canada , USA and South Africa pay due attention to this date.