Welcome to You Ask Andy

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 compounds 

Certain 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 


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