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In here, you are jumping ahead of yourself and getting muddled.

a few steps you need to go through include learning about electron levels/shells and the number of electrons in each level.  Look at the periodic table and the number of electrons in the outer shell - which is the key thing that determines it's chemical properties.

Let's take lithium and fluorine since you put them in above.

The lithium atom has 3 electrons. 2 fill the core shell (first level has a maximum of 2 electrons).  This means there is one electron in it's outer shell.  To get the full compliment of electrons in the outer shell it would need to pick up 7 electrons which in energy terms would be HUGE and so completely not happening.  So the easiest thing for it to do is lose that spare electron to another atom that wants to fill it's own shell.

Lithium can completely give it's electron away to say fluorine which needs one electron to fill it's outer shell with. Because Li completely transfers it's electron over to F - they become ions. Li+ and F-
The anion (F-) is attracted to the cation (Li+) and so they hang about together through ionic bonding.  But F- now 'owns' that electron.

Now atomic mass is not always directly equated to the number of electrons because you can have isotopes which have extra neutrons, the particles with no charge.  But protons and electrons will be the same number of each in an atom.

Elsewhere in the periodic table we have atoms that need a number of electrons but instead of completely giving or taking electrons, they share them. Covalent bonding.

Some atoms have a greater affinity for electrons.  oxygen is one of those. but tricky because it has lone pairs and can form multiple bonds which i will only confuse you with at this point.

So let's take your methane molecule in the main post.
Carbon has it's snug pair of electrons in the core shell. They are happy. But, carbon needs 4 electrons for it's outer shell to gain the full compliment and thus be energetically stable.  It is not energetically favourable to give away or receive 4 electrons in the sense that Li can give away one and F can gain one.

So Carbon shares.  Each H atom only has one electron and needs 2 to fill it's shell and be energetically stable.  

So an H shares it's one electron and C shares one of it's electrons to pair up. So they cheat a little bit in filling their shells.  

4 H atoms share with one C atom so that C 'borrows' 4 to fill it's outer shell and each H 'borrows' one to fill it's outer shell.  In reality, these electrons whizz around all over the place, so the H electron can be found anywhere over the molecule, not just around the H atom, the all mix in together to form an electron cloud that holds the molecule together. But that is another model.

Will it help if I tell you the kind of music I like so that you can dig out other stuff for me to try listening to?

by In Wales (inwales aaat eurotrib.com) on Fri Mar 14th, 2008 at 10:18:25 AM EST
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