Re: Why... (OT)
- From: crissy <ms_crissyX@xxxxxxxxx>
- Date: Wed, 2 Jul 2008 22:42:42 -0700 (PDT)
On Jul 2, 11:48 pm, of mice and monkfish <fonkm...@xxxxxxxxxxx> wrote:
On 2 Jul, 10:16, Mandy <mandy...@xxxxxxxxxxxxxx> wrote:
of mice and monkfish <fonkm...@xxxxxxxxxxx> wrote in news:d089876d-1189-
448f-9ca0-eb7f3cef2...@xxxxxxxxxxxxxxxxxxxxxxxxxxxx:
On 1 Jul, 18:19, Mandy <mandy...@xxxxxxxxxxxxxx> wrote:
Hiya everyone
Why does it hurt when you get salt in a cut?
Interesting question, Mandy!!!
I only asked cos we were eating chips last night and they had obviously
been salted at the chippy and I've got a cut on my finger and some salt
obviously went in it! lol
It's one of those things that we all take for granted and never
really stop to ask ourselves /why/ something is the way it is. So
like i say, it's an interesting question. It made me stop and think.
I'm not 100% sure about this answer, but after thinking a little bit
about it in my brain, i'd say it's something to do with the effect of
sodium ions on nerve transmission.
Those ions get everywhere! lol What *are* they though?
I was really hoping someone would've bailed me out by explaining this
for me. It's years since i've done any proper chemistry, but i'll do
my best.
In their original state - as they are represented in the periodic
table of elements, for example - atoms are comprised of a nucleus of
neutrons and protons, with electrons occupying a series of shells
orbiting the nucleus.
There are always the same number of neutrons as protons (except in the
case of hydrogen, whose nucleus is just one proton on its own, poor
thing), and there are always the same number of protons as
electrons.
Neutrons have no charge, protons are positively charged, and electrons
are negatively charged. Because there are the same number of protons
as electrons, the overall electrical charge of the atom is zero.
The negative electrons and the positive protons cancel one another
out.
I hope you're still with me.
Now, different atoms have different properties, and one of the most
important factors that determines some of these differing properties
is the arrangement of the orbiting electrons in their shells around
the nucleus. Each shell can only hold so many electrons, so when one
is building a model of an atom, one starts with the inner-most shell,
which only holds two, and then we move to the next shell, which holds
eight, and so on until we are all out of electrons.
I'm going to cheat here and include a link to a diagram on wikipedia
of a sodium atom:
http://en.wikipedia.org/wiki/Image:Electron_shell_011_Sodium.svg
Sodium has eleven electrons, so working from the inside out, the first
shell has a full complement of two, the second shell has a full
complement of eight, and the third shell just has one on its own. We
write this down as 2, 8, 1 - look at the diagram to see how these
numbers correspond to the layers of the 'onion'.
The lone 'outer electron' is of vital importance in terms of
understanding the chemical properties of sodium.
In chemical reactions, very often what takes place is an exchange of
outer shell electrons. Atoms like sodium are keen to lose their one,
or in other cases two, outer shell electrons - thus leaving only the
full complement of eight electrons in the next orbital as the outer
shell - while atoms like chlorine need only one electron to complete
their outer shell.
We can verify this for ourselves if we look at the configuration of
electron shells in the chlorine atom, which has seventeen electrons in
total. So putting two in the first shell and eight in the second, we
find we have seven left over in the third - one short of the full
complement of eight. Where can chlorine get this extra electron
from? A sodium atom!
In terms of electron shells,
Sodium = 2, 8, 1
Chlorine = 2, 8, 7
Sodium and chlorine thus react well together. The sodium atoms lose
their one outer shell electron, giving it to the chlorine atom, and
thus both gain stability by being together. But if you remember, the
only reason why atoms have no overall electrical charge is because
there are an equal number of positively charged protons and negatively
charged electrons. When we start swapping electrons amongst different
atomic nuclei, we end up with particles that have an unbalanced number
of electrons and protons, and thus have an overall electrical
charge.
These we call 'ions'.
In our example of sodium and chlorine reacting together, because the
sodium is losing a negatively charged electron, the sodium ion has an
overall positive charge of +1 (it has one more proton than
electrons). At the same time, the chlorine atom is /gaining/ a
negatively charged electron, and so the chloride ion has an overall
negative charge of -1.
If we look at the electron shells in this pair of ions, we can see the
difference this reaction has made.
Sodium ion = 2, 8
Chloride ion = 2, 8, 8
Both ions have a full electron shell of 8, and hence each has found a
much greater degree of stability than it had before.
When sodium and chlroine react together, we get sodium chloride -
otherwise known as salt.
From this it follows that atoms are more stable (less reactive) if
they already have a full complement of electrons in their outer
shell. The noble gases, for example, are famous for being almost
completely unreactive. If we take a look at the electron shells of
the first few members of this group, we can see why.
Helium has only two electrons in total, so its outer shell is the one
that holds only two, and hence is complete. Neon has ten electrons,
so its configuration is:
Neon = 2, 8
Again, we see that the outer shell is complete, this time with eight
electrons.
This is how it is with argon:
Argon = 2, 8, 8
Here we see the same thing again - as with all the other gases in this
particular group, the outer shell is complete, and so they are
unreactive.
The opposite is the case with the group one elements (so-called
because they have but one outer shell electron):
Hydrogen: 1
Lithium: 2, 1
Sodium: 2, 8, 1
Potassium: 2, 8, 8, 1
The single solitary outer shell electron is much easier to spot this
time, and makes these elements highly reactive.
Conversely, if take a quick gander at the halogen group of elements,
we find these are all lacking just one electron to make their outer
shell complete
eg.,
Fluorine: 2, 7
Chlorine: 2, 8, 7
Like the group one elements, these are also highly reactive - and as
we have already seen in the sodium chloride example, group one
elements and halogens react well together, precisely because each has
what the other is lacking, and they find it easy to lose or gain
electrons in the process of chemical reaction, and thus form more
stable ions.
And that, in very loose terms, is what an ion is.
Now, i hope you've understood all that - there'll be a test
tomorrow!!!!
<monkfish laughs evilly and rubs has hands together>
I skipped all this - knew it already - seems like you do what I do
sometimes, when answering apparently simple questions; my children now
start with a proviso before they ask me anything - that they want the
simplest shortest explanation - lol
.
- References:
- Why... (OT)
- From: Mandy
- Re: Why... (OT)
- From: of mice and monkfish
- Re: Why... (OT)
- From: Mandy
- Re: Why... (OT)
- From: of mice and monkfish
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