Exactly how many different atoms are there?
Our world is made from an endless assortment of solids, liquids and gases and all these countless substances are made of atoms. But the list of different atoms is very short. We know, more or less, how many different atoms are found in nature but new discoveries are being made all the time. Today's list of atoms may be longer next week or next year,
If we could separate the atoms in the earth's crust, almost half of them would be atoms of oxygen. The atomic number of oxygen is 8, which means that every oxygen atom has eight protons in its nucleus and eight orbiting electrons. Oxygen has been given the atomic weight of 16, but a few oxygen atoms weigh more than their brothers because they have extra neutrons in their nuclei.
There are oxygen atoms with weights of 17 and 18. Oxygen 15 and 19 are radioactive atoms breaking down into smaller atoms. All these assorted oxygen atoms, however, have the atomic number 8 and the same chemical properties. They are all isotopes of the chemical element oxygen. Most of the chemical elements have brother isotopes. If we count these isotopes as different atoms, we have a list with about a thousand items.
The list of chemical elements is much shorter. In nature, there are 92 different chemical elements, but most of them are so rare that we never meet them in everyday life. Same are radioactive elements such as uranium, busy breaking down into small atoms. Eight of the natural elements are so plentiful that they make up more than 98% of the earth’s crust.
But these 92 elements with their thousand or so isotopes is not a complete list of the different atoms. Scientists have discovered and even created more elements in the radiation laboratory. Eleven more elements have been added to the list since 1940 and the number of known elements is now 103, Next week or next year, the list may be longer.
The chemical elements are arranged on a neat chart of rows and columns. This is the Periodic Table which can give a wealth of information at a glance, On the basis of this orderly arrangement, the chemist can predict what the elements with atomic numbers from 104, but he cannot tell exactly how many different atoms will finally be discovered.
The chemists of 1770 knew of only 20 chemical elements, Eleven more were discovered in the next 25 years and in 1869 the list had grown to 63. The proper arrangement of the wonderful Periodic Table was solved at the start of World War I and when your parents were born the scientists had discovered only 88 of the 92 elements from which our world is made.