i was trying to think of why there are electron pairs.
is the reason: that sub shells have electrons in pairs, and so this is why the electrons are in pairs.
what happens if there are 3 electrons in the outer shell spare? there will be one pair and then one lone electron? what happens with the repulsion there?
and then there area bonded electron and a lone electron pair, how does that happen?
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Fantastic thinking, Lewis! What might be useful is to draw dot-and-cross diagrams for some of the shapes that we worked out in yesterday's lesson. You'll then be able to see where the lone pairs come from and which electrons are involved in bonds.
In terms of the sub-shells, you're right in that electrons 'go round in pairs' because they occupy orbitals that can contain up to 2 electrons. However, the electrons won't pair up unless they have to. For example, nitrogen has 7 electrons. The first 2 fill up '1s' in Energy Level 1, then the remaining 5 electrons are in Energy Level 2. 2 of these electrons will be in '2s' and the other 3 in '2p' BUT the 2p electrons will each go into separate orbitals as this minimises repulsion between them. (Are you familiar with this from Mr Beaumont's lessons?) This means that there are 3 unpaired electrons that can form covalent bonds with other atoms (e.g. 3 Hs to form NH3) leaving 1 pair of electrons (the '2s' electrons) that does not bond and is the 'lone pair'. However, this lone pair can form a dative covalent bond with another atom, such as H+ to form NH4+.
Hope this long ramble makes sense! It's quite difficult to explain without the use of diagrams!
I am very impressed with all your great thinking and additional reading that you have clearly been doing this evening! See you next week.
Would it ever happen that the 3 electrons in 2p don't form covalent bonds, and don't need to, because another element can form a dative covalent bond, filling the outer shell? ie. Can those three electrons ever be lone pairs, or will they always bond covalently to other atoms?
Again, an interesting question, Vicky... Can you think of anything that would make it less likely for another atom to form a dative bond to N in order to complete its outer shell?
my head hurts.
thank you.
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