[mikewday]

I'm looking for a simple program that will tell my daughter what molecules can be made from different starting atoms. For instance, if I have just one oxygen and 2 hydrogen, I can make H2O. What if I choose these 4 atoms, what molecules can I make? Anything out there that would do this?

[Borek]

No such thing. There are huge databases containing many molecules, some of the free (like chemspider), but even that won't be of much help. Trick is, there are often many isomers, so the number of possible molecules (especially in the organic chemistry) grows exponentially (if not faster) with the number of atoms.

[mikewday]

Thank you for the quick reply!
I was trying to explain to my daughter (5th grade) a little detail about atoms forming molecules in the simplest way possible. I like the Lewis dot diagrams which make it seem kind of like clicking Legos together but that seems to only hold up for a limited set of atoms. I have not read enough yet to understand exactly why but I know there are different orbitals etc and it's much more complicated.
Following the simple Lewis dots and wanting 8 electrons in the outer shell, it seems like Phosphorus, Magnesium, and Hydrogen could combine but, if I search Chemspider (awesome, thanks for the site), I don't see it listed.
Is there a subset of atoms that will work in just about any combination where each atom has access to 8 electrons in the outer shell?
Bascally, I wanted her to be able to draw some molecules and we could look them up. But, I don't want to give her options that would not be valid.
I appreciate any help. I want to learn more but have limited time to self teach. Is there a subset of atoms I could give her and she could go crazy combining them and they would make valid molecules?

Thanks!

[Corribus]

Explaining why some atoms combine and others don't is practically the entire basis of chemistry. As you can imagine, there is no catch-all, simple explanation. You'd have to start from square one with a general chemistry text and just start reading.

Based on your description, I would suggest investing in a basic organic chemistry modeling kit. Most of the atoms in the upper right quadrant of the periodic table WILL bond together in various ways (Except the far right column.) and they are represented in most modeling kits.  You can then look up some basic molecules that maybe you've heard of and see if you can build them with a modeling kit (acetone, ethanol, octane, chloroform etc.). I think this would be an appropriate place for a 5th grader to start tinkering around. You're not going to learn the nuances of orbitals and chemical bonding this way, but you will start to learn things about the types of things that are generally allowed (how many atoms a carbon will bond to, what a double bond is, etc.).

Search amazon or ebay.