#1
What determines the shape of the final molecule in a bond??

and

How do you assign oxidation numbers to a compound? Why would you want or need these oxidation numbers??


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#4
Repost in the science/math help thread and I'll help you.
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#5
the shape of a molecule is determined by the number of charge clouds or electron domains around the central atom. For instance, H2O has 4 charge clouds around the central atom; two charge clouds connect the hydrogen atoms, and two charge clouds for the two lone pairs (lone pairs are pairs of electrons not bound to other atoms but circle the central atom). In the normal case with four charge clouds in which all four charge clouds connect to atoms, the molecule shape is called a tetrahedral; however, in this case, there are only two atoms connected and two lone pairs. You don't take lone pairs into account when determining the shape of a molecule, so in this case water takes on the "bent" geometry.

Oxidation numbers are assigned by the electronegativity of atoms in a compound. Electronegativity is a fancy word for saying how strongly an atom pulls on electrons. You can usually determine the oxidation numbers of atoms by looking at how many electrons they need to gain or lose in order to complete their outer shell. Again lets look at H2O. Oxygen has an oxidation number of -2, because it needs to gain two electrons to complete its outer shell. Because the overall charge on H2O is zero, the two hydrogens must each have a +1 charge to balance out the oxygen. Oxidation numbers are important because once you start doing redox (reduction oxidation) reactions, one of the methods for find the solution is called the oxidation number method, and it requires you to know the oxidation numbers of atoms in the compounds in order to see where electrons flow in a reaction.

Hope this helps
#6
Quote by angelfire2006
the shape of a molecule is determined by the number of charge clouds or electron domains around the central atom. For instance, H2O has 4 charge clouds around the central atom; two charge clouds connect the hydrogen atoms, and two charge clouds for the two lone pairs (lone pairs are pairs of electrons not bound to other atoms but circle the central atom). In the normal case with four charge clouds in which all four charge clouds connect to atoms, the molecule shape is called a tetrahedral; however, in this case, there are only two atoms connected and two lone pairs. You don't take lone pairs into account when determining the shape of a molecule, so in this case water takes on the "bent" geometry.



This ones wrong though. You do take lone pairs into account, hence why water is bent and not linear.
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#7
Quote by darthteet
This ones wrong though. You do take lone pairs into account, hence why water is bent and not linear.

lone pairs are taken into account for where the visible atoms are placed in the compound, but not for the overall shape. lone pairs only affect the visible atoms; they are not viewable themselves
#8
Quote by angelfire2006
lone pairs are taken into account for where the visible atoms are placed in the compound, but not for the overall shape. lone pairs only affect the visible atoms; they are not viewable themselves


You didn't say that though. And 4 valence electrons isn't exactly the "normal case".
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#9
I'll give you a much more simple definition for molecular shape. There are set rules, the shape is determined by the number of lone pairs and bond pairs around the central atom, for example:

2 bond pairs and no lone pars would yield a linear shape
2 bond pairs and one lone pair would yield a bent shape with bond angles of 107 degrees
2 bond pairs and two lone pairs would yield a bent shape with bond angles of 104.5 degrees
3 bond pairs no lone pairs would yield a trigonal planar shape with bond angles of 120 degrees
3 bond pairs and one lone pair would yield a tirgonal pyrmaidal shape with bond angles of 107 degrees
3 bond pairs and two lone pairs would yield a t shaped molecule with bond angles of 90 degrees
4 bond pairs and no lone pairs would yield a tetrahedral molecule with bond angles of 109.5 degrees
4 bond pairs and one lone pair would yield an irregular tetrahedral (or see saw) shape with bond angles of 120 and 90 degrees
4 bond pairs and two lone pairs would yield a square planar shape with bond angles of 90 degrees
5 bond pairs and no lone pairs would yield a trigonal bipyramidal shape with bond angles of 120 and 90 degrees
5 bond pairs and one lone pair would yield a square pyramidal atom with bond angles of 90 degrees
6 bond pairs and no lone pairs would yield an octahedral shape with bond angles of 90 degrees

Yeah I have to memorize them for chemistry so I figured it'd be good practice to write them all down.
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#10
Quote by darthteet
You didn't say that though. And 4 valence electrons isn't exactly the "normal case".
thought it was implied. oh well it made sense to me. and i'm not sure what you meant by 4 valence electrons? i said "normal case" referring to how 4 charge clouds normally take the shape of a tetrahedral which is true, though there are exceptions (like water). and if you want to be technical 4 "valence electrons" is the normal case in a world called organic chemistry
#11
Quote by angelfire2006
thought it was implied. oh well it made sense to me. and i'm not sure what you meant by 4 valence electrons? i said "normal case" referring to how 4 charge clouds normally take the shape of a tetrahedral which is true, though there are exceptions (like water). and if you want to be technical 4 "valence electrons" is the normal case in a world called organic chemistry


so true.
#12
Quote by angelfire2006
thought it was implied. oh well it made sense to me. and i'm not sure what you meant by 4 valence electrons? i said "normal case" referring to how 4 charge clouds normally take the shape of a tetrahedral which is true, though there are exceptions (like water). and if you want to be technical 4 "valence electrons" is the normal case in a world called organic chemistry



I'd wager that there were a lot more octahedral complexes than tetrahedral ones.

Also, carbocations are pretty damn important. Though oddly enough, the electronic structure of carbon tends to dominate carbon chemistry. Whodda thunk it?
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#13
you really don't have to memorize each molecular geometry.

you just have to remember how the lone domains affect the bonded domains.
VSEPR or electron geometry helps a lot to memorize. But once you relate the actual shapes to each VSEPR model, all you have to remember is which bonds get replaced by lone pairs.


The TS' questions are all answered already, so that's all I have to say.
#14
Quote by darthteet
I'd wager that there were a lot more octahedral complexes than tetrahedral ones.

Also, carbocations are pretty damn important. Though oddly enough, the electronic structure of carbon tends to dominate carbon chemistry. Whodda thunk it?


*cough*

#15
Quote by darthteet
I'd wager that there were a lot more octahedral complexes than tetrahedral ones.

Also, carbocations are pretty damn important. Though oddly enough, the electronic structure of carbon tends to dominate carbon chemistry. Whodda thunk it?

octahedral has 6 charge clouds though and not four so i'm not sure how that's relative.

second sentence is over my head
#16
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*cough*


D. I've not done organic in months. I'll be doing again next semester though.

Quote by angelfire2006
octahedral has 6 charge clouds though and not four so i'm not sure how that's relative.

second sentence is over my head



You said that 4 was the normal. However it's not really. It's just the one most common in organic chemistry.
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