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# VSEPR for 2 electron clouds

The valence shell electron-pair repulsion (VSEPR) model is used to predict the shapes of molecules and polyatomic ions. VSEPR is based on the idea that the “groups” or “clouds” of electrons surrounding an atom will adopt an arrangement that minimizes the repulsions between them. In this video, we look at examples of molecules in which there are two groups of electrons around the central atom. Created by Jay.

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• At , how does one know carbon does not have a formal dot charge of zero? •  Try calculating the formal charge. Remembering that the formula for formal charge is [# of valence electrons] – [electrons in lone pairs + 1/2 the number of bonding electrons]. So carbon has four valence electrons, right? Moving on to lone pairs, we can see that there are no lone pairs, so we can plug a 0 in for that. Finally, there are a total of 4 electrons in the bonds, but only half of these electrons go to the carbon (think about what a covalent bond is and this will make sense). So taking what I've said above, 4 valence - 0 lone pair electrons - (1/2)(4 bonded electrons) = 4-0-2 = 2+. Now, you could even look at the formal charge of the oxygens and it should make more sense as to why you take those pairs of electrons and put them into the double bonds (keeping in mind that 0 formal charge is the best on atoms). Hope this helped! ( I took the formula from http://www.masterorganicchemistry.com/2010/09/24/how-to-calculate-formal-charge/ and I think it's a good link to look at!)
• What do you do if there ARE lone pairs on the center atom? • The short answer is that the initial configuration is determined by how many electron regions exist on the central atom. Then, the molecular geometry is determined by considering how many actual atoms are in the structure, as opposed to electron pairs.

For example, if you are considering water (H20) which has a central Oxygen, with two pairs of electrons, bonded to two Hydrogen atoms.

The central Oxygen would have 4 regions, one region for each of the electron pairs, and one region for each of the single bonds to hydrogen. As a result, it's initial geometry would be tetrahedral.

Now, not all of those 4 regions are filled with an atom so we have to think about what happens if only half of those regions are filled. (The video on VSEPR 4 can better illustrate this.) What you want to keep in mind is that the atoms want to be as far apart from each other as possible, and the electron pairs repel atoms a little more then atoms repel atoms. With this in mind, the tetrahedral is drawn with atoms on one side, electrons on the other. The final molecular geometry ends up being bent.
• Going by this, the H2O molecule would seem to qualify for 2 electron clouds and linear geometry with a bond angle of 180 degrees. Why is it instead considered "bent" geometry with a bond angle of 104.5 degrees?

Apologies if there is a video that addresses this and I haven't seen it yet. • Isn't Be has a full octet?
I see only two bonds connecting Be and two chlorine atoms.
I thought it should be double bond and there might be two lone pairs for each of chlorine atom . • Be does not obey the octet rule: Be seeks 4, not 8 electrons. Thus, Be (unlike the other members of Group 2) makes only covalent bonds.

While there are other elements that do not follow the octet rule (H, He, Li and usually B), Be is rather unique in many of its properties.
• At how come we don't put 2 more lone pairs of electrons on Be? • At he says that you can find Beryllium in group two on the periodic table. None of the tables I've looked at have group numbers. How can if find the groups->number of valence electrons on a periodic table? • why does carbon not have a formal charge of 0 • Formal charge = valence electrons - lone pair electrons - bonds

Using this formula, carbon has a formal charge of 0 when it has 0 lone pairs and 4 bonds.
4 - 0 - 4 = 0

If carbon dioxide looked like O-C-O with 3 lone pairs on each oxygen, then carbon only has 2 bonds so it has a formal charge of +2 (4 - 0 - 2 = +2) and each oxygen has a formal charge of -1 (6 - 6 - 1 = -1)
In the structure with 2 double bonds (like O=C=O) all atoms have a formal charge of 0.
• What is the difference between electron domain geometry and molecular geometry?
(1 vote) • hi there, my question is does a radical count as 1 electron cloud? For example, is NO2 bent (if a radical counts) or linear (if a radical does NOT count). Also, is the nitrogen in NO2 sp2 or sp hybridized? Thanks in advance!  