GCHEM questions from Kaplan

[xaznxcountx]

---

Members don't see this ad.

1. According to the VSEPR Theory, the H-TE-H bond angle in H2TE should be closest to:

a. 90
b. 120
c. 109.5
d. 149.5
e. 180

The answer is actually C, but I don't understand why because I thought the 2 pairs of lone pair electrons would cause repulsion and lower the angle to be lower than 109.5.

2. Boron found in nature has an atomic weight of 10.811 and is made up of the isotopes 10Boron (mass 10.013 amu) and 11Boron (mass 11.0093 amu). What percentage of naturally occurring boron is made up of 10Boron and 11 Boron respectively?

a. 30, 70
b. 25, 75
c. 20, 80
d. 15, 85
e. 10, 90


Any help is greatly appreciated... Please provide an explanation too if you understand it well. Thanks all!

 

[tranv117]

1. According to the VSEPR Theory, the H-TE-H bond angle in H2TE should be closest to:

a. 90
b. 120
c. 109.5
d. 149.5
e. 180

The answer is actually C, but I don't understand why because I thought the 2 pairs of lone pair electrons would cause repulsion and lower the angle to be lower than 109.5.

2. Boron found in nature has an atomic weight of 10.811 and is made up of the isotopes 10Boron (mass 10.013 amu) and 11Boron (mass 11.0093 amu). What percentage of naturally occurring boron is made up of 10Boron and 11 Boron respectively?

a. 30, 70
b. 25, 75
c. 20, 80
d. 15, 85
e. 10, 90


Any help is greatly appreciated... Please provide an explanation too if you understand it well. Thanks all!

for the first, just think of water...

for the second, I think someone asked this not too long ago.

just remember, %(isotope1) +%(isotype2) + etc. = atomic weight. Sorry, Im just lazy to type it all out, but you should get the idea.

 

[AndyK]

The first one is a mistake. Published results indicate that the H-Se-H bond angle is very close to 90. It would follow that H-Te-H would be similar if not acute.

 

[xaznxcountx]

The first one is a mistake. Published results indicate that the H-Se-H bond angle is very close to 90. It would follow that H-Te-H would be similar if not acute.


Yeah I thought it was close to 90 degrees. WTH... so what is the right answer then?


BUMP 👍

 

[Contach]

What the hell are you talking about?

H-Te-H or H-Se-H are going to look the same as H-O-H. This is because they all have the same valence electron configuration - the central atom has 2 lone pairs and 2 bonding pairs of electrons. On a test situation we know that the H-O-H bond angle is about 109.5.. a bit less because of the repulsion from the lone electron pairs.. actually 104.5. But I don't think they want you to know the 104.5, but instead that it's a bit less than 109.5.... but quite a bit more than 90... It is clearly NOT 90 degrees because that would be octahedral geometry.. the H-O-H or H-Se-H or H-Te-H will be bent MOLECULAR GEOMETRY, or TETRAHEDRAL ELECTRONIC GEOMETRY.. hence where the 109.5 degrees comes from....

Someone who read 'this published article' tell me how they justify the bond angle to be 90 degrees.. because if this was the case.. there would be no symmetry...

First I want to see the proof for these published studies. Secondly, you are not meant to know this information. In general chem you rely on the concepts (as explained above) to figure out the answer - not published articles that only a nerdy chem major knows about... No the question isn't wrong. The concepts are there for you to figure out the angle shape. If you put 90degrees for this answer - you will get it wrong.

 

[AndyK]

What the hell are you talking about?

H-Te-H or H-Se-H are going to look the same as H-O-H. This is because they all have the same valence electron configuration - the central atom has 2 lone pairs and 2 bonding pairs of electrons. On a test situation we know that the H-O-H bond angle is about 109.5.. a bit less because of the repulsion from the lone electron pairs.. actually 104.5. But I don't think they want you to know the 104.5, but instead that it's a bit less than 109.5.... but quite a bit more than 90... It is clearly NOT 90 degrees because that would be octahedral geometry.. the H-O-H or H-Se-H or H-Te-H will be bent MOLECULAR GEOMETRY, or TETRAHEDRAL ELECTRONIC GEOMETRY.. hence where the 109.5 degrees comes from....

Someone who read 'this published article' tell me how they justify the bond angle to be 90 degrees.. because if this was the case.. there would be no symmetry...

First I want to see the proof for these published studies. Secondly, you are not meant to know this information. In general chem you rely on the concepts (as explained above) to figure out the answer - not published articles that only a nerdy chem major knows about... No the question isn't wrong. The concepts are there for you to figure out the angle shape. If you put 90degrees for this answer - you will get it wrong.

Ask and you shall receive... and next time don't be so hostile

here's another one from a textbook if you don't believe the other one.

 

[Albuterol]

What the hell are you talking about?

H-Te-H or H-Se-H are going to look the same as H-O-H. This is because they all have the same valence electron configuration - the central atom has 2 lone pairs and 2 bonding pairs of electrons. On a test situation we know that the H-O-H bond angle is about 109.5.. a bit less because of the repulsion from the lone electron pairs.. actually 104.5. But I don't think they want you to know the 104.5, but instead that it's a bit less than 109.5.... but quite a bit more than 90... It is clearly NOT 90 degrees because that would be octahedral geometry.. the H-O-H or H-Se-H or H-Te-H will be bent MOLECULAR GEOMETRY, or TETRAHEDRAL ELECTRONIC GEOMETRY.. hence where the 109.5 degrees comes from....

Someone who read 'this published article' tell me how they justify the bond angle to be 90 degrees.. because if this was the case.. there would be no symmetry...

First I want to see the proof for these published studies. Secondly, you are not meant to know this information. In general chem you rely on the concepts (as explained above) to figure out the answer - not published articles that only a nerdy chem major knows about... No the question isn't wrong. The concepts are there for you to figure out the angle shape. If you put 90degrees for this answer - you will get it wrong.

LOL u tell em' contach