What is an element?

Do you find salt (NaCl) in the periodic table? but you do find ‘Na’ and ‘Cl’, isn’t it!

Do you find H₂O in the table? but you do find ‘H’ and ‘O’, isn’t it!

Seperation

You can separate salt from a mixture of salt and sand. Isn't it?
 

Sorting out substances from one another is called separation.  We apply separation technique in our daily life often.
 

So if you take a substance and If it can be separated into two or more substances, we say it is impure, or a mixture of substances. In other words, if you cannot separate a substance into two or more substances after using all different methods, the substance can be considered to be pure or just that only substance.

But there is a problem in defining a pure substance in this way. The problem is that you may have tried all the methods that you know about today for separating a substance. Maybe the substance cannot be separated by any of these methods. So you think the substance is pure. But it is possible that a scientist could discover some new method of separating such a substances in future. It is possible that the substance you thought was pure today could then be separated into different substances, using this new method.

For example, suppose you draw water from a well and filter it with a filter paper. Suppose all the water passes through the filter paper without leaving a deposit.

What would you conclude about this water?

Now suppose you heat this water and some deposit is left behind after the water has evaporated.

Would you now consider this water to be pure?

Over several centuries this is what chemist have been working on. They developed kinds of separation techniques and applied to various substances.

For example when you apply electrolysis, you find the water can be broken down or separated into Hydrogen and Oxygen. Since you can not further separate Hydrogen and Oxygen you believe that they are the fundamental constituent substance. We started calling them into Elements. * (about electrolysis)

Lets take the case of phosphorus’

The period was 17th century.
 

There was one alchemist in Germany, Henry Brand. it was believed that Human urine may contain the philosophers stone, that has the ability to turn any metals into gold.  Mr. Brand was trying to find a method to separate this philosophers stone from Urine.
 

He followed the following process

He let the urine stand for days  until it gave off a terrible smell. Then he boiled it down to a thick paster. Then in heated this thick past to a very high temperature and let the vapours though a water. What he got was a waxy substance that glowed in the dark.

This was the 13th element discovered.
 

When then known separation methods were applied it could not be further separated into other substances.
 

After separating one substances from another they finally reach conclusion that there are these substances, we call them elements, are the basic building block of all the diversity of matter around us.

Then the other question that followed was - what particles these elements themselves are made up of, what is the difference between say hydrogen and oxygen, what makes them different?

But before that lets learn about another important tool of learning chemistry - how to name these elements and substances.