Carol Chursenoff, age 13, of Van Nuys, Ca.
How do atoms and molecules differ?
The smallest possible known piece of iron is an atom of iron It takes about 100 million of these iron atoms to measure one inch and each of these little iron atoms is like its neighbors We find a description of the iron atom at the top of column eight on the Periodic Table of chemical elements Its atomic number is 26, which means there are 26 proton particles ire the core or nucleus of each iron atom There art also 26 electrons swarming about the nucleus and electrons control the chemical behavior of an atom The atomic number, then, tells the scientist how iron, for example, ‑can combine with oxygen to form rust
All material things are made from a hundred or so different elements such as iron and oxygen, hydrogen and carbon, sodium and chlorine The atomic number tells how many protons charged with positive electricity are in the atoms from which each element is made Since a normal atom has an equal member of protons and negatively charged electrons, it also tells how many electrons swarm about the nucleus
The elements iron and oxygen combine to form rust, which is a compound The elements hydrogen and oxygen form water, which is also a compound Table salt is a compound of the elements sodium and chlorine Wood is made mostly from cellulose, a compound of carbon, hydrogen and oxygen The assorted atoms in these compound, however, are not all mixed and fumbled together They are bound together in neat units with so many and no more to a package Each unit is the smallest possible particle of a compound, just as an atom is the smallest possible particle of an element
The smallest unit of table salt contains one atom of sodium and one of chlorine and the number of these units In a single grain of salt can be written as 10, followed by 24 zeroes
Each unit of water contains one atom of oxygen and two of hydrogen Each unit of cellulose contains six atoms of carbon, 12 of hydrogen and five of oxygen
At one time, all these units were called molecules Molecule was a class word used to describe the smallest part of any compound, just as atom is a clans word used to describe the smallest part of any element But nowadays, certain experts insist that table salt must be described in terms of ions and the compound water must involve such terms as covalant bonds and hydrogen bonds This proves that the expert knows what he is talking about, but it leaves us without a general term for the smallest parts of all compoundsCertain scientists, however, still use the word molecule for this purpose, especially when they are explaining things to the non‑expert So, until science settles on a general term for these units, we too may call them molecules