Ionic Compounds and the Crystalline Lattice Stucture They Make

[Chasse]

Hello,

 

just wondering about ionic compounds and why they come together to form crystalline lattice structures (when they are solid.) It seems to me that in order to form a crystalline lattice structure, each molecule (or formula unit) needs to be attracted to each other. And since NaCl, for example, is supposed to have a neutral charge, one molecule of NaCl should not be attracted to another NaCl molecule (or anything else for that matter.)

 

I can understand covalently bonded compounds being attracted to one another and clumping together, since they share electrons and will be slightly polar due to the sharing. But ionic compounds do not share electrons they transfer electrons and thus should be neutral in charge (since Na will have a +1 charge and Cl a -1 charge when chemically bonded, the charges should cancel out exactly.) A neutrally charged particle shouldn't be attracted to another neutrally charged particle, at least not to the point it makes a crystalline lattice structure.

 

I'm also trying to figure out how an "excited" atom is supposed to chemically bond with another atom since electrons will jump up to another energy shell when excited. For example, sulfur will have 6 electrons in it's outer shell when it's in it's ground state (room temp and ambient light?) and not excited. But if sulfur is excited to the point where an electron jumps up the outer energy shell, then it would have 7 electrons in it's outer shell and behave more like chlorine (or any other halogen), wouldn't it? If 2 or 3 electrons are excited there's no way it should bond. And wouldn't exciting these electrons break up a compound when already bonded? Then there's the fact that orbitals are just probabilities and they stray outside those probabilities from time to time.

 

And last but not least, can somebody tell me why it is so important for an atom to have it's outer shell completely full? So important that electrons leave it's own atom (with the protons they are attracted to) to join another atom that is charge neutral and give it a negative charge?

 

thanks,

Chad

Edited March 23, 2010 by Chasse
Afterthoughts

[farmboy]

Hello,

 

just wondering about ionic compounds and why they come together to form crystalline lattice structures (when they are solid.) It seems to me that in order to form a crystalline lattice structure, each molecule (or formula unit) needs to be attracted to each other. And since NaCl, for example, is supposed to have a neutral charge, one molecule of NaCl should not be attracted to another NaCl molecule (or anything else for that matter.)

 

I can understand covalently bonded compounds being attracted to one another and clumping together, since they share electrons and will be slightly polar due to the sharing. But ionic compounds do not share electrons they transfer electrons and thus should be neutral in charge (since Na will have a +1 charge and Cl a -1 charge when chemically bonded, the charges should cancel out exactly.) A neutrally charged particle shouldn't be attracted to another neutrally charged particle, at least not to the point it makes a crystalline lattice structure.

 

Your problem here is that you should never really be looking at NaCl as a discrete molecule, it needs to be examined as part of the lattice it exists in. Even though the net charge of a molecule of NaCl would be 0, each of the constituent atoms is really a seperate charged entity that will bond to 6 atoms of opposite charge aruond it creating a lattice.

 

 

I'm also trying to figure out how an "excited" atom is supposed to chemically bond with another atom since electrons will jump up to another energy shell when excited. For example, sulfur will have 6 electrons in it's outer shell when it's in it's ground state (room temp and ambient light?) and not excited. But if sulfur is excited to the point where an electron jumps up the outer energy shell, then it would have 7 electrons in it's outer shell and behave more like chlorine (or any other halogen), wouldn't it? If 2 or 3 electrons are excited there's no way it should bond. And wouldn't exciting these electrons break up a compound when already bonded? Then there's the fact that orbitals are just probabilities and they stray outside those probabilities from time to time.

 

TBH, I'm not really 100% on what you're asking here. What specific reactions are you talking about when you say that they can't go ahead with an excited electron? I think your problem may stem from the fact that you are using a very simplified version of the atom. When you are considering bonding from a quantum mechanical view point, there are significantly more factors to take into account than simply the number of electrons in the outer shell. The concept of the outer shell even becomes irrelevant. Sorry, that explanation probably doesn't help you very much.

 

And last but not least, can somebody tell me why it is so important for an atom to have it's outer shell completely full? So important that electrons leave it's own atom (with the protons they are attracted to) to join another atom that is charge neutral and give it a negative charge?

 

thanks,

Chad

 

It's not important for an atom to have a full shell, its only important that you know it 'prefers' to have a full shell. The reason it likes to have a full shell is because that configuration is the lowest energy configuration and so is the most stable. You may or may not know that (in simple terms) all systems are constantly striving to have as little energy as possible. This is an extremely important concept in chemistry,