[ThomasV]

Hello chemical forums, for a huge project for school I chose to try and make glasses from crystals (huge mistake). Now since my research failed I am going to have to explain how it works on a micro-scale.

My question is: What bonds can be present in crystals?

From what I've gathered I understand that apart from the standard ionic bond, covalent bonds can also appear depending on the ions the crystal is made up of. Also, dipole-ion bonds are possible due to bonds between H20 and the ions. But are induced dipole-ion bonds possible within the crystals (so without outer help)? And are dipole-dipole and hydrogen-bonds present between the water molecules in de crystal? I assume London dispersion forces won't appear in crystals because it's made out of ions and water molecules.

Thanks in advance!

[AWK]

Generally, all possible types of bonds occur in crystals. Some crystals do not contain ionic bonds - such crystals are called molecular crystals. Metal crystals have specific bonds called metallic bonds.

[ThomasV]

Thank you for the reply.

 Do you know if in for example alum crystals, the h2o molecules will bond? In an image from http://www.chemspider.com/Chemical-Structure.56418.html they seem so close together. Will they form dipole-dipole bonds or hydrogen bonds? I find it hard to get any information about it when browsing.

[AWK]

The alum crystal consists of sulfate ions, [Al (H2O) 6] 3+ ions, and potassium ions coordinated by 6 water molecules.

[ThomasV]

Are they not bonded but just sorted like that?

I think I should have stated what I wanted to do first, sorry for that. I am trying to understand what bonds influence the hardness of a crystal. So my new question is: Do the water molecules form dipole-dipole bonds or hydrogen bonds with each other or with the salt that influences the hardness of the crystal? Or are they just there to hold it in place?

Thank you for your time

[AWK]

Ask yourself why diamond (carbon crystal) is the hardest known material?

[ThomasV]

I thought it was because it is only made out of covalent bonds. And covalent bonds are the strongest types of bonds. Now you mention it, I understand that dipole-dipole bonds will have no real effect on the hardness. But won't hydrogen bonds have an effect? I've read that they are a lot stronger than "van der Waals bonds".

[AWK]

The hardness of ice is only due to the hydrogen bonds between water molecules, but it is incomparable to diamond. The hardness of NaCl is due only to ionic bonds, but is incomparable to that of a diamond. Also, many metals (e.g. Os, W) are quite hard, and their hardness is mainly due to the metallic bonds.

[jeffmoonchop]

Each of the coordinated complex ions in alum are hydrogen-bonded to each other in a repeating pattern down each of the three dimensions. Most of the time when you have a structure with so much water coordinated to ions the repeating pattern is caused by hydrogen bonding.