MadSci Network: Chemistry

Re: why is salt water a better conductor of electricity than sugar water?

Date: Fri Feb 19 13:19:10 1999
Posted By: Brian Dolan, Undergraduate, mathematics/bio-cybernetics, Pierce College
Area of science: Chemistry
ID: 919127715.Ch

This is one of those questions that goes straight to the heart of
chemistry, so its answer is fairly important.  There are two things you
nedd to keep in mind to answer it:

1) The nature of chemical bonds and

2) The nature of electricity.

Of course, you can always skip to the next to last paragraph, but if you
really want to know, you should read the whole thing. . . 

I'll do the first one first (good idea, no?)

1) There are two types basic types of chemical bonds: IONIC and COVALENT. 
Remember, a chemical
bond is the way two atoms stick together to form a molecule.  For
instance, common salt is the combination of two atoms, sodium (Na on the
periodic table, #11) and chlorine (Cl, #17).  If you look at the periodic
table, you'll notice that they are on opposite sides.  Sodium is on the
left and chlorine on the right.  When they come together the form NaCl, or
sodium chloride, or table salt.

ANother thing you need to know is that the atoms (or elements) on the left
side of the periodic table form positively charged ions, and those on the
right form negatively charged ions.  An ION, you remember, is simply an
atom that has gained or lost and electron to make it have a charge.
Sodium LOSES and electron and therefore loses a single negative charge,
moking sodium overall POSITIVE.  Chlorine picks up an electron and makes
it overall NEGATIVE.

When two charged atoms (ions) come together, they form an IONIC bond.  So,
by definition, an ionic bond has charged particles in it.  That's what
happens with salt, NaCl.

Ionic bonds tend to break up in water, covalent bonds don't.  When the
ionic bonds break, they leave the ions floating around in the water as
charged particles.  That's important.

If two or more atoms from the right side of the periodic table form a
they share their electrons (that is, they don't give them up like ions
do) and form a COVALENT bond. Covalent bonds,
simply, are bonds between atoms that are not charged.

2)  Okay, almost done.  Electricity is carried by charged particles.  A
good conductor of elelctricity would be, say, a sodium ion, Na+, or a
chlorine ion, Cl-.  (See where this is going?)  Covalent bonds do not have
charged particles AND they don't break up in water.

Okay, last thing, then you can re-read this and make sure you understand

Salt, as we already said, is an ionic compound.   When dropped in water,
it breaks up and leaves charged particles (ions).  Sugar is made of carbon
(C, #6) hydrogen (H, #1) and oxygen (O, #8).  THey are all on the right
side and therefore make COVALENT bonds which do NOT break up in water and
carry NO charge.

Whew!  I hope you take the time to look at your periodic table and see
where everything is located.  I also really really hope you do more
chemistry, it's a wonderful science and there's so much to learn.

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