chemistry experiments for children

different kinds ofatomsin a molecule changes, the substancebecomes com-
pletely different.
IfH is the symbol forhydrogen,then what does H 2 mean?H is oneatomof
hydrogenalone;but the 2 in H 2 means there are twoatomsof hydrogen, so H 2
must be a molecule. H 2 is one molecule of hydrogen which contains two
atomsofexactly the same kind,thatis,hydrogen.Canthis be trueof02'too?
Yes, one molecule of oxygencontainstwo oxygen atoms.
Now if the smallnumbersin thesubscriptrepresentthenumberof atoms in
one molecule, what do the bignumberswrittenon the same linemean?Look
at thisequation:
2H 2 +O 2 - 2H 20
The big 2 infrontofH 2 showsthatthere are twohydrogenmolecules. Each
ofthese moleculescontainstwoatomsofhydrogen. The subscript2 says so.
Thenhow manyatomsofhydrogenarerepresentedhere?Four.Having two
moleculesoftwoatomseach is like having two bags eachcontainingtwo apples.
Alltogetheryou'dhave four apples. The big 2 infrontof theformulaforwater
meansthatthere are also two moleculesofwater. But in eachofthese molecules,
thereare three atoms, twoofhydrogenand oneofoxygen. If there arethree
atomsin one molecule, then there are six atoms in two molecules. But remember
thatthemathematicalproportionsare always the same in moleculesofthe same
substance.In these two water molecules there are four atoms ofhydrogenand
two atomsofoxygen. This is like having two bags, eachcontainingtwo apples
andone lemon, or atotalof four applesandtwo lemons.
Why are these largenumbers necessary?Because ofanotherofthe basic
lawsofnature,the onethatsays:Mattercannotbecreatedordestroyed;only
its form can be changed. This is the Law ofConservationofMatter.If you
wrote: H 2 +O 2 - H 20 you would be describing an impossible reaction.
Youwould bethrowingaway oneatomof oxygen,somethingthatnot even the
greatestscientists in the world can do. Inorderfor an equationto tell the
truthandaccountfor all the atoms,bothsidesofit must be balanced. Oneof
the things you must do then tocorrecta wrongequationis tobalanceit by
changingthe numbers. You can'tchange thesubscriptnumbers, though,be-
cause the LawofDefiniteProportionssays theratioofdifferent atoms in one
kindofmolecule mustremainthe same. Youcan'tthrow in new atoms orthrow
outold ones either because the LawofConservationofMattersaysthatmatter
cannotbecreatedor destroyed. The only numbersyou can change, then,. to
balance an equation are the numbers of molecules. Instead of saymg
H 2 +O 2 - H20,you must say:
2H 2 +O 2 - 2H 20