containingatoms of morethanone element. The way a chemist uses numbers
in this scientificshorthandshows theproportionof different kinds of atoms in
the molecules of acompound.By agreeing to use the same systemofsymbols
and formulas, the chemists have made it possible for every scientist to under-
standany chemical reaction written in the language of chemistry. Even when
scientists of different countries speak different languages, the language of
chemistry remains the same andunderstandableto everyone.
Now, using the atoms of the commonelements, let's look at how this
language works. You will seethatit is really simple.
Agis the symbol for the element silver.Clis the symbol for the element
chlorine. When made to react with each other,a silveratomand achlorine
atomcombine to become a molecule of silver chloride, orAgCl.Here is how
thisreactionlooks whenstatedin the language ofchemistry:
Ag+Cl----+AgCl
Thisformulastatesthatoneatomof silver and oneatomof chlorine become,
or, to use a more technical term, yield one molecule of silver chloride. The
statementitself is in the form of an equation.No numbersare used when a
"I"would be theappropriatenumber;the"I"is understood.But this does not
necessarily meanthatonly oneatomof silver and oneatomof chlorine were
involved.Perhapsthe reaction involved several million atoms of each kind.
Atomsare so tinythatitprobablyinvolved many more thanthat.Whatthe
understood"I"does mean isthatforeveryoneatomof silverthatjoinedone
atomof chlorine,onemolecule of silver chloride was formed.
Nais the symbol for sodium. See if you can explain what thisequationmeans:
Na+ci-.NaCI
Whenever two or more atoms remain bound together, they make up a
molecule. Inorderfor molecules to be of the same kind, the atoms theycontain
must be present in the same relative numbers. Thisconsistentgroupingof the
same numbercombinations in one kind of substanceis called the Law of
DefiniteProportions.You are surely familiar with theformulafor a molecule
of water, H20.It doesn'tlook like AgCl or NaCl. It has a 2 in it, and the 2 is
written as a smallsubscript(somethingwrittenbelow the line). Thisformula
saysthatone molecule of watercontainstwo atoms ofhydrogen(the H) and one
atomof oxygen (the0).Whenevertwoatomsofhydrogenunite withoneatom
ofoxygen, the result is one moleculeofwater. This is one of the basic laws in
chemistry. How would you explain thisformula:H 202 ?It represents one mole-
cule,ofcourse, butnotof water. In water the ratio(the relativeproportion)
is 2 to 1; in this molecule the ratio is 2 to 2.Thereforeitcan'tbe water.It's
hydrogen peroxide (the same peroxideyou use on cuts). When the ratioof
lily
(lily)
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