I understand that table salt is sodium chloride (ionic bond of sodium and chlorine). I’ve also heard that ingesting pure sodium or pure chlorine can be fatal. (Any truth to this?) In addition, I remember from high school chemistry that (when added to water) NaCl will separate into sodium and chlorine ions. So why don’t I die from sodium and/or chlorine poisoning when I drink salty water?
Yes, pure sodium is toxic. It is also explosive upon contact with water (it’s stored in oil for this reason). So if you put a piece in your mouth, your head would basically explode.
Pure chlorine is also completely, totally, and inarguably toxic to breathe, and very hazardous to get on your skin.
The sodium and the chlorine combine into a stable configuration, that’s why you can eat salt without your head exploding. For the same chemistry reason, hydrogen, which is an explosive gas, and oxygen, which is a flammable gas, combine to make water, which is not a gas at all, let alone explosive OR flammable.
Just one of the Wonders of Chemistry. 
I understand that when they’re joined in an ionic bond a stable molecule is formed, but in water the ions separate, correct? So aren’t we back to a dangerous situation again?
No, they do not separate into sodium and chlorine in water.
NaCl,when added to water,seperates into ions.They are different from pure sodium or pure chlorine which are neutral atoms while ions are charged.Ions,under normal physical conditions,are stable.If the water is removed,they combine back to give molecular NaCl.In solution,molecular NaCl almost doesn’t exist.
In order to form,say,pure sodium,the positive sodium ion has to ‘grab’ an electron from the negative chlorine ion.This usualyl doesn’t happen because chlorine atom holds onto that electron tightly while the sodium atom doesn’t want that electron back.
No. Here is what an “ion” is:
When you dissolve salt in water, it doesn’t break down into separate sodium and chlorine ions. The sodium atoms and the chlorine atoms stay stuck together to form the molecules known as “sodium chloride”, and it’s a very powerful chemical bond.
So the sodium chloride molecules, when they dissolve in water, get a positive or negative charge that makes them into ions. They float around in amongst the water molecules, but they remain sodium chloride molecules, not sodium atoms and chlorine atoms or “ions”.
It’s the elemental form, the sodium and chlorine “atoms”, that are dangerous.
“Ion” just refers to whether an atom or molecule has an electrical charge.
The ions do indeed separate, to the extent I’ve heard it said that salt water doesn’t contain any salt moleculesper se, but only loose ions floating around by themselves. But that’s just the point. It’s not the ions that are hyperreactive, it’s the uncharged atoms. Put an uncharged sodium atom next to a chlorine atom, and BANG! you have a molecule of NACL. But put a Cl+ ion next to a Na- ion, and they just slide idle past one another…
Elemental sodium reacts with water, producing sodium hydroxide, hydrogen gas, and heat. The reaction itself is not explosive, it simply is very rapid and tends to produce a hydrogen-fueled flame. This is why holding touching elemental sodium is a bad idea. However, when bonded to chlorine, the sodium does not react with the water. Most of it exists in an ionic form in solution. Sodium and chlorine ions, because they are in solution, do not pose the dangers that elemental sodium and chlorine do. Sodium chloride is a good way to get them into solution with dealing with elemental forms, and can make a plate of french fries much tastier than they would otherwise be.
To elaborate further.
In solution,NaCl—>Na+ + Cl-
Na+ is a sodium atom minus an electron while Cl- is a chlorine atom with that electron joined to it.They are stable and it would take a lot of chemical energy under special conditions to donate that electron back to the sodium ion,which doesn’t happen in animals,usually.
(actually it does happen partially,which is why there is hydrochloric acid in the stomach and sodium bicarbonate in bile.The process is a little complicated and enzyme-activated)
Molecules are different from ions which are different from atoms.
NaCl,when solid is a molecule.
In water,they do seperate into Na+ (sodium ion) and Cl- (chlorine ion).
Sodium and chlorine atoms are simply Na and Cl.These are the ‘dangerous’ ones.
So you’re saying if I ate a plateful of pure sodium ions, and (later) washed it all down with a scrumptious helping of pure chlorine ions, then I would feel no ill effects?
Well,you’d never be able to isolate the ions.They always co-exist as positive and negative pairs.
Actually,you can create sodium and chlorine using electricity.It’s not so simple but briefly:The negative terminal of the battery donates an (negative)electron to each sodium ion creating a sodium atom but this practically doesn’t occur because sodium hydroxide is formed.(that’s why industries use molten sodium chloride rather a solution,since sodium and water don’t go well together).
The chlorine ion(Cl-)donates an (negative)electron to the positive terminal and chlorine atoms are formed.Since the positive and negative terminals slowly begin to approach neutral,the battery is slowly exhausted.
To quote South Park “Remember children, there are no stupid questions - just stupid people” Just kidding.
First off Sodium (Na): Na is two rows below H on the periodic table. Without going into a discussion of electron orbitals and their relative stabilities just know that if two elements are in the same column on the periodic table the one in the lowest row is the more reactive. When you drop elemental sodium in water you get this basic reaction (this is assuming pure water in a vacuum and equal stoiciometric propotions if there are any smart asses out there)
Na2 + H2O -> Na2O + H2O
Na steals the O from H and burns. Real flames too - I’ve seen it. Very cool. As to it being fatal, remember we are mostly water. Imagine eating a big hunk of burning napalm. It would also steal O from almost any molecule it pumped into. Basically all Hell would break loose.
Chlorine: Cl2 is an extremely toxic heavy green gas. I won’t go into the biochemistry (because I can’t remember it) and just tell you never ever mix muriatic acid with bleach.
So why isn’t Na+ Cl- (NaCl in its ion form)?
Short answer: it’s the ionic bond. An ionic bond is one where atoms “give” electrons to other atoms. It is an extremely stable bond that needs something very reactive to break it. Na2 and Cl2 are covalently bonded and “share” electrons. This isn’t so stable. The dissassociated ions in water have already traded electrons so they are stable and won’t react with much, including the molecules that make up you - so there not toxic.
This took a while to write so forgive me if someone already answered.
Beeblebrox
"Ford, you’re turning into a penquin, stop it.
Chemistry teacher wanders by…
This is incorrect. As Javaman alluded to, the ions indeed separate. The reason this happens is because the ions hydrate, that is, they are surrounded by polar water molecules. Water molecules have one “side” that is slightly positive, and one side that is slightly negative, making them polar. In solution, the ions have water molecules to take the place of their oppositely charged counterpart.
Also, ionic compounds do not form molecules. Molecular compounds, like water and methane, do. If you like, you could think about solid NaCl being like one really big “molecule,” composed of a 3-D “grid” of many, many quadrillions of alternating ions. It is incorrect to think of NaCl being composed of 2 ions making up a single molecule. Chemists refer to one pair of ions as a “formula unit,” not a molecule. (At least chemists teaching general chem, and trying to be as correct as possible do.) 
As Trucido mentioned, the reaction of Na with water is not in and of itself explosive. Because the reaction produces hydrogen gas and heat, the hydrogen gas ignites when oxygen is present. This is a different reaction (combustion of hydrogen). In an oxygen-free environment, there will be no flame.
Also, Na[sub]2[/sub] does not exist. It is simply Na (s).
As for the OP, it is very important to realize that in chemistry, the ionic form of an element behaves completely differently than the neutral form.
Also, Na[sub]2[/sub]O is not stable in water. A hydroxide is produced instead. (And I think you meant hydrogen gas, not water, as a product.)
The correct reaction is:
2Na (s) + H[sub]2[/sub]O (l) --> 2NaOH (aq) + H[sub]2[/sub] (g)
Whoops–didn’t balance the %$#@ equation! That should be:
2Na (s) + 2H[sub]2[/sub]O (l) --> 2NaOH (aq) + H[sub]2[/sub] (g)
So then to take this a step further then since NaCl in solution still tastes “salty” we must be tasting either the Na ion or the Cl ion (or both) rather than tasting the NaCl molecule as a whole.
zombie or no
calcium chloride is used for saltiness.