Lets Talk About Ammonium

[Bignose]

In really short, a covalent bond occurs when electrons are shared between molecules. This sharing can be strong or weak, depending on how many electrons are shared and what atoms they are shared from and with.

Ionic bonding occurs because of charges. That is, a molecule with a positive charge is attracted to one with a negative charge, almost exactly like the poles of a magnet.

Water (H2O or H-O-H) and carbon dioxide (CO2 or O=C=O) are covalent bonds. In water's case, the oxygen borrows 1 electron from each of the hydrogen atoms and that bonds the hydrogen and oxygen atoms together. In carbon dioxide's case, the carbon atom borrows 2 electrons from each oxygen atom to form the bond. That's why water is written with a single dash (to indicate one electron being shared) and carbon dioxide is written with 2 dashes (to indicate 2 electrons being shared).

Comparatively, look at sodium chloride (table salt) NaCl. This is one sodium atom Na+ with one chlorine atom Cl-. The sodium ion, Na+ is positive because it readily gives up one electron (is is called an electron donor). It gives up that electron because the atom is actually more stable by giving up an electron. Similarly, chlorine is an electron acceptor. Is is more stable when it accepts a free electron. But, because the two atom have lost an electron or gained an electron, respectively, they are no longer neutral. They are charged and opposite charges are attracted to one another.

Ionic bonding can be very strong (i.e. table salt doesn't spontaneously break into sodium and chlorine gas -- both very dangerous chemicals on their own) or weak (the ions usually will separate in a water solution, only to reform when the water is taken away).

Covalent bonding is usually what organic compounds (those with oxygen O, carbon C, hydrogen H and nitrogen N) participate in. Ionic bonding is usually what inorganic compounds participate in. Usually, not always. There are organic ionic bondng, like nitrite and nitrate (NO2- and NO3-) salts, and there are inorganic compounds that can form covalent bonds (sulfer can, for instance). So, it isn't always the case, just usually.

Also, sometimes the distinction between the two isn't so clear cut. Because of the way oxygen shares the electrons from the hydrogen atoms, there is actually a partial charge created. The hydrogen from one water molecule is attracted to the oxygen from another water molecule. This is known as hydrogen bonding, and it one of the main reasons water has such a high boiling and melting point compared to other similar substances. In order to boil water, you have to tear a molecule from all the hydrogen bonding it participates in.

There is obviously a lot more to this than can be written just here. Any good organic chemistry book, or even most good 1st semester university level texts should discuss covalent and ionic bonding in a lot more detail.

 

[Bignose]

I just think that it should be clear that while the shell theory is a very good model that is good at helping predict a lot of the known behavior, it is important to note that the electrons don't actually travel around the atom's nucleus in "shells" or "orbits". That model of the electron spinning around the nucleus like a planet orbiting the sun on the solar system is really quite inaccurate, and has been proven wrong for well over 60 years now. Electrons actually jump all around the nucleus, making a "cloud". Electrons don't travel in smooth circles or ellipses like an orbiting body, they change direction frequently, and go up and down, left and right, forwards and backwards, as near as well can tell today completely randomly. They don't actually organize themselves into those "shells". But, the model is still very good at explaining things like bonding, so it is still taught, but it is only a model, not a representation of reality. Kind of like how in an introductory physics class, everything is assumed to be frictionless, or a tossed ball doesn't experience wind resistance -- these are models that are useful for teaching and explaining concepts -- but in reality nothing is frictionless and wind resistance is obviously a significant factor. That doesn't mean that we shouldn't teach about frictionless ideas, just acknowledge that frictionless is merely a useful model and that is has it's limitations. Same thing with the shell theory of electrons. It is a very useful model, but it has its limitations.

 

[Miss Wiggle]

i think i need to go re-sit GCSE science!!!

thansk for the explanations guys, will have a proper read through it all later on, about to head out right now.

 

[aaronnorth]

I expected bignose correcting me on some of it because they dont actually teach you the full truth at GCSE, as they say it is to much to get your head around! So when you actually come to A-levels you have to more or less forget half of it lol.

 

[Bignose]

I expected bignose correcting me on some of it because they dont actually teach you the full truth at GCSE, as they say it is to much to get your head around! So when you actually come to A-levels you have to more or less forget half of it lol.

Well, I think that it is important to note that "the full truth" about atoms and molecules isn't known -- probably far from the full truth. The shell model is just simply that, a model. It doesn't bear a whole lot of relation to reality.

But, again, that doesn't mean it isn't useful to teach and to keep teaching. It is remarkably good at predicting a great deal of bonding, such as H2O or NH3. In that regard, the model is spot on.

Einsteins' relativity basically 100% proved that Newtonian physics is wrong. Experiment after experiment have shown Einsteinian physics correct time and time again. Things like GPS wouldn't work without properly taking in to account general relativity. Nevertheless, what is the entire first physics text that undergraduate physics and engineering majors take? Newtonian physics. And again, even in those texts, there are literally hundreds of problems would have little or no relation to actual reality. Massless pulleys and frictionless bearings and air resistant ignoring balls are everywhere. But, again, the point is to teach the basics and build up. Use the simplified model to start the students down the right path, then add more reality, more complexities.

It is the same thing with the shell model of atoms. The shell model does very good, in it's limited area. But, I also think that it is very important to note that the models of the atom with the electrons spinning around the nucleus -- again like planets around the sun -- is very, very wrong. Even though it is seen everywhere, and it still very common in a lot of texts. So, again, while the shell model is very useful, don't confuse it reality. It is a great way to solve the issue of how many electrons would need to be shared by each atom to make it stable, but the electrons do not in anyway travel around the nuclei of the atoms in shells.

There are even some common molecules where the shell model isn't perfect. Benzene rings are a good example. Shell modeling says that a carbon in a benzene ring should share one electron with the carbon to one side, and share two electrons to the carbon on the other. But, the actual testing of the bond strength of the carbon to carbon bonds in a benzene ring indicate that the strength is actually equivalent to the carbons sharing one and a half electrons with each of the carbons on each side. The shell model doesn't permit half electrons. It deals with whole electrons only. So, it doesn't really model the benzene correctly compared to what is observed in reality. But again, it is a very good starting point to build knowledge off of. And, yes, sometimes you do have to forget what you have been taught. Even when you've been taught seemingly something very correct that works, because it is only an approximation or a newer better theory that explains the old phenomena and more has come along. That is how science grows.

That is how this section grows.

 

[aaronnorth]

Thanks for the answer, i have a test on this next week!

Is it also true that if all the electrons line up in a straight line that we would be able to put something through it, take a brick wall for example?

 

[Bignose]

Is it also true that if all the electrons line up in a straight line that we would be able to put something through it, take a brick wall for example?

I'm not sure what you mean by this, could you expand your question a little bit?

 

[andywg]

I assume it is the theory that if you were to have all the atoms and subatomic particles line up exactly one would be able to walk through a wall due to the large amount of space one usually associates with the world at an atomic level (I seem to recall seeing on BBC that if one has a proton and a neutron to form a Hydrogen nucleus at roughly tennis ball size then to place the electron in the first cloud at the right distance would involve being something like 27 miles away).

 

[aaronnorth]

Andy has got it. When i went off the forum i realised i had put electrons instead of particles

I seem to recall seeing on BBC that if one has a proton and a neutron to form a Hydrogen nucleus at roughly tennis ball size then to place the electron in the first cloud at the right distance would involve being something like 27 miles away

That is very interesting, and amazing if true!

 

[Bignose]

Oh, I get it now. Yes, there is a relatively incredible amount of empty space in an atom. The experiment that proved the nucleus theory of atoms was pretty simple, really. The researchers made a very thin layer of gold foil -- only a few atoms thick. Then they shot alpha particles (H+) at the foil. Behind the foil was a detector, a sheet of zinc sulfide that lights up when hit by an alpha particle. Turns out, the overwhelming majority of alpha particles goes right through the sheet. That is only possible if the atom is actually largely empty space. Because if it wasn't, the alpha particles should be bounced backwards and the to the sides -- definitely not straight through.

 

[LauraFrog]

That's an interesting study actually - do you know who did it? Might be useful for a chem assignment.

According to posters on the Koi Vet forum, who usually know what they're talking about (I will dig up the link):

Ammo lock gets rid of ammonia by converting it to something else entirely. The active ingredient in Ammo lock is sodium hydroxymethanesulfonate, which binds irreversibly with ammonia to form aminomethanesulfonate which is totally non toxic. There are some chemical formulas for these substances on the koi vet forum but some must be wrong because they are different. I'm not sure that any are right but some just don't make sense.

 

[rabbut]

The gold foil and alph-particle scattering experiment was done by Ernest Rutherford in the early 1900's

 

[Miss Wiggle]

well i've done loads of reading of this and the links provided in my lunch break today. think i'm starting to remember some science..... but i sitll have a few q's, apologies if these have already been answered and i've missed it, but could you just hold my hand with this a bit please..... i'm no good at science!!

1 - do we actually know that what products like ammo-lock do is convert (all or some of) the ammonia to ammonium thus reducing the toxicity?

2 - am i correct in understanding that ammonia and ammonium can form a covelant bond then? if they have formed a covelant bond does it have any effect on the toxicity of the ammonia/ammonium in the water or not?

 

[aaronnorth]

in answer to number 2:

does ammonium & ammonia form covelant bonds?

I can see ammonia doing it as N needs 3 more electrons so 3 Hydrogens fill the outer shell, but how does ammonium do it?

Thanks

Ammonia is neutral, but the molecule can accept an H+ without too much of an energy barrier to overcome. Then the ammonium can participate in ionic bonding.

The covalent bond doesnt affect the toxicity (in this case) ammonia is found as NH3, (or produced through the Haber Process ) If we spit this back into Nitrogen and hydrogen, then it would be safe, but as shown above with the diagrams, they are not stable in this present condition so by sharing electons, they are pretty unreactive.

covelant bond is just a bond, it doesnt change anything in terms of toxicity.

 

[Miss Wiggle]

thanks, thats what i thought..... just wanted to be sure i'd understood correctly!