Structure of sodium chloride and diamonds

[ATB_roo]

Considering the structure of sodium chloride, why does solid sodium chloride melt when it is heated strongly, and why does molten sodium chloride conduct electricity?

Also,

Considering the detailed structure of diamond, why is the melting point of a diamond higher of that of sodium chloride?

Thanks in advanced! (I totally don't understand ionic bonding and all that crap :P)

[Zevon]

soory but you'll have to understand ionic bonding but here goes.
fisrt of all diamond is composed entirely of carbon atoms each with 4 covalent bonds to each other. A covalent bond uis the strongest type of bond between atoms and having 4 of them means that each atyom is very strongly connected to each other atom.
Sodium chloride is ionically bonded, this bond is relativley weak and can be broken or disrupted quite easily and even water can break ionic bonds by polar bonds. This explains why NaCl has such a low melting point compared to diamond.
Also when ionic bonds are broken, as when NaCl is melted, they can act as free electrons and conduct charge. meaning they conduct electricity.
Basically the negative chorine ions conductt electricity and when molten are free to move.

[Gef]

Sorry but I don't entirely agree with Zevon.

The bonds in sodium chloride are reasonably strong ionic bonds and so it has a fairly high melting point of 801C. In the molten state it is composed of sodium and chloride ions which can move about and so carry an electric current. There are no free electrons.

In diamond, as Zevon correctly states, each carbon atom is covalently bonded to 4 others. These are very strong bonds and so diamond (and graphite) are not easily melted. In fact these substances do not melt but sublime (turn into gaseous carbon atoms). There are no charged particles and no moblie electrons in this state and so they don't conduct.

Solid graphite conducts unlike diamond as only 3 of the outer electrons are used to form covalent bonds and the fourth is free to move around and carry a current.

[Zevon]

I only said ionic bonds were relatively weak to covalent bonds and that the ions acted as free electrons.
Please read carefully, as you know science is complex junk and requires a full reading of complex words to split the hairs of said junk. ; )

[shammydodger]

In particular for diamond, because the bonds are all identical, the bond angle between carbon atoms is the optimum tetrahedral bond angle of 109 degrees 28 minutes, which explains the particularly stable 3D structure of diamond and, hence, the high melting point.

[Gef]

Zevon, I do read carefully. Ions and electrons are totally different. Also the strength of ionic and covalent bonds vary considerably. Some covalent bonds are much weaker than some ionic bonds and vice-versa.

[Zevon]

Relative as in regard to. Ergo the ionic bonds in NaCl are RELATIVELY weak compared to the covalent bonds in diamond. When discussing two things and the term rellatively is used it means comparing the two. And although ions and electrons are totally different, leptons and atoms, but the ions act as free electrons by conducting the charge. Act: verb meaning to behave like or behave as in given circumstances.

[Gef]

Ions do not act as free electrons. Electrons can only carry a current in solid conductors such as metals and graphite. Ions can only carry a current in solution or in a molten ionic compound. Pupils at GCSE level get penalised for confusing the two.

[Zevon]

The question stated molten sodium chloride and free electrons can conduct charge in any medium, seeding air wirth electrons is a way of conducting and extending lightning as well as ionised air. A current flow is defined as the movement of charged electrons and so as ions carry this charge then they represent current and can be said to act as a flow of free electrons.
Also electrons can conduct through air in the case of statsic electricity and in a vacuum in a free electron alser and in a gas from neon lights.
GCSE students are taught hoorible generalisations. 3 circular Energy shells anyone?

[Zevon]

P.S. Ions in air conduct lightning as well, not just in solutions.

[Gef]

zevon, I apologise. Of course the molecules in air do become ionised during lightning strikes. However, the rest of your answers are just rubbish. A free electron is just that ; it is NOT an ion. As for your thoughts on electrons shells - do you advocate teaching young pupils about s,p,d and f orbitals etc?

[Zevon]

The point I was trying to make was that your comment about pupils losing marks at GCSE was irrelevant as GCSE is not correct.
And for thwe last time "ACT AS" not "IS". I never said ions were electrons. An ion is a charged atom or molecule - I Know this. but in a molten ionic compound the ions act as free electrons with respect to electro-conductivity, the topic being discussed. You admit that they both carry charge and therefore you must see that in electro-conductive behaviour negative ions and free electrons are behaviourily indistinguishable. No experiment based on electroconductivity could discern between the two, therefore they must be considered as the same within this frame of reference. Therefore the two are one and the same, adn as such act as one another.

[Gef]

For the last time before I give up. Electrons are negatively charged. Ions can be positively or negativelty charged. Electrons can flow through metals, ions connot. Ions flow only in ionic solutions or molten ionic compounds, electrons do not. Obviously you have never studied GCSE chemistry or anything similar.

[shammydodger]

Gef

I have to side with Zevon in this instance. Return to his initial post. He says "they can act as free electrons." He doesn't say they are free elctrons. Your initial reply, the part that argues against Jevon, says that there are no free electrons in sodium chloride. Jevon never said or implied that there are. He has being trying to argue that point ever since and yet you refuse to acknowledge it.

[Zevon]

Thank You Shammy

Oh and Gef I did GCSE hemistry in 2005 and am now stuying A2 chemistry and Physics. This stuff is fresh in my mind and I know what I mean. Evidently Shemmy can also tell what I mean. It is only you who seems to have difficulty understanding what I mean.

[Gef]

Soory for the delay but I have been away for a long weekend. I have a degree in Chemistry and have been teching it for the past 31 years. This is a topic often misunderstood by students.