AP Chemistry VSEPR Theory?

Question

According to the VSEPR model, the arrangement of electron pairs around NH3 and CH4 are
A. Different b.c in each case there are a different number of atoms around the central atom
B. Different or the same, depending on the conditions leading to maximum repulsion.
C. the same because both nitrogen and carbon are both in the second period
D. different because in each case there are a different number of electron pairs around the central atom
E. the same because in each case there are the same number of electron pairs around the central atom

Answer 1

NH3 has 3 pairs of bonded electrons, and one lone pair, while CH4 has 4 bonded pairs, so both have a steric number of 4. However, loan pairs are more repulsive than a bonded pair of electrons, so that will push the 3 hydrogens on ammonia farther away, so technically you could argue that they are arranged differently, but it sounds like just a poor choice of wording in the question, so I think the answer they're looking for is E.

Answer 2

N = 5 valence electrons
3 H = 1 x 3 = 3 valence electrons

N will have one lone pair and 3 bond pairs.

C = 4 valence electrons
4 H = 1 x 4 = 4 valence electrons

C will have 4 bond pairs.

E. They both have the same number of electron pairs around the central atom. Molecular shape differs although not asked for in the question.

Answer 3

I will be the contrarian and say that the answer is "A".

According to the VSEPR, NH3 has 4 bonding sites and only 3 pairs of shared electrons. Its shape is pyramidal because of the distortion from the unshared pair.

CH4 has 4 sites and 4 pairs of shared electrons. There are no unshared pairs and the shape is tetrahedral.

This description is best fit with answer "A"

Answer 4

I'm taking AP Chemistry without Chemistry, and I think its not that bad. As long as you do the homework on time, study like 3 hours for every test, READ THE BOOK, and do a lot of practice problems, then you should get a good grade. I am a sophomore in AP Chem, and I do all of the things I listed above, and I have a 98 in the class. As long as you practice and try really hard, AP Chemistry is not that bad without Chemistry first. But I'd definitely take Chemistry before AP Chemistry, I asked many kids in my AP chem class if it makes it easier, and they said it does. Taking Chemistry before ensures that you have the basic chem concepts down, so next year in AP chem you come ready to dig deeper into those concepts you previously learnt, instead of first learning those concepts in AP chem without chem.

Answer 5

E. There are four pairs of electrons around both N and C, with three of them bonding in NH3, and four of them bonding in CH4. The four pairs of electrons are arranged tetrahedrally to minimize repulsion of each other.

Answer 6

D

Answer 7

D