For students taking Chemistry 101 at the University of Victoria in the Fall 2013 term.

Wednesday, September 14, 2011

Chapter 1

Any questions on Chapter 1 material? Ask them here.

33 comments:

Anonymous
said...

Hi,

In class on Wednesday you talked about Homework Assignment 1, and I just wanted to clarify that this is not for marks. Also, the deadline for it is September 17th at 1:28pm, does this mean that it will not be available after that time?

If you went through the process, all should be well - but even if it didn't work, the system will register your responses against your clicker serial number, and all those who haven't yet registered successfully will get another warning from me.

For us luddites without smart phones, where can we access the answers for the questions in our course pack/youtube videos of the answers? I'm not seeing them on the site...

Why would the electron drop from an excited state to a ground state when the element is heated? It's absorbing energy from the heat so it needs to give off energy in the form of a photon because?

Hi Caitlin You mean like when Caleb sprayed different salt solutions into the flame? The thermal energy is enough to evaporate the solvent, convert ions to atoms, and excite some atoms into an excited state. However, this state is unstable with respect to the ground state, as it is much higher in energy, so it can fall back down to the ground state, thus emitting a photon (yellow for sodium, green for boron, etc). If you keep heating, this process keeps happening, i.e. atoms will keep being excited and keep emitting photons, as energy is being constantly introduced in the form of thermal energy. Remove the heat source, and the process will stop - there is not enough energy to promote electrons into an excited state.

Thanks I see now that the electron first is raised to an excited energy level because it has been given thermal energy but then it drops because the excited state is unstable. This happens continuously throughout the heating process. So the electron goes up and then down every time (and every time it goes back down a photon is emitted). This is indirectly related to any kind of preservation of energy concept (energy is given off because it has been absorbed)?? Am I on the same page as you, Professor?

now that we've covered the entire chapter and im sufficiently brushed up and ready to attempt some practice quizzes, they're past the deadline. although i can see the questions, i cant see the answers

There is only one 1s orbital, so degeneracy is irrelevant in this case. There p orbitals display degeneracy, which simply means that these 3 orbitals (px, py and pz) have the same energy. So do d and f orbitals (five and seven degenerate orbitals, respectively).

practice quiz 1 covers some pretty funky, unrelated junk. question 10, for instance:

The triviance of the standard laboratory nard is directly proportional to its feebity in poods and inversely proportional to its frumiance in arbols. If the units of triviance are nils, what must be the units of the proportionality constant?

The Chapter 1 questions in our notes uses the equation 1/wavelength=(Rydberg Constant)*(1/ni^2-1/n2^2) for question 4. It's not in our list of equations on our periodic table, however. Do we need to memorize that equation?

They have the same energy. For your purposes, orbitals with the same value of n and l. So the three 2p orbitals are degenerate, as are the 5 3d, the 7 4f, etc. Hydrogen is exceptional in that all orbitals with the same value of n are degenerate, e.g. the 2s and 2p orbitals are the same energy. This is NOT true for multi-electron atoms, however.

I thought the question on our online quiz #2 "The correct ground-state electron configuration for molybdenum is __________." was a little unfair. From the rules we've learnt, you would assume that its configuration was [Kr]5s2 4d4. I understand that for atoms (such as Cr), a more stable configuration results when a d orbital is half filled (or completely filled), therefore yielding [Kr]5s1 4d5, however, we were only told to look out for Cr and Cu.

I feel like we shouldn't really be expected to know electron configuration anomalies other than the ones taught in class or in the text.

1.Is there a way to relate the number of maxima to each orbital such as the nodes relate to each orbital (n-1)? Eg( how many maxima will a 4s orbital have? Or 1s?)

2.I got a different answer for this question because I used nfinal = 4 and ninitial = 2: The electron residing in the 2p orbital of an electronically excited hydrogen atom is promoted to the 4dxy orbital by absorption of a photon light. The longest wavelength of light that can be emitted by the resulting electronically excited hydrogen atom is:

In the solutions they used nfinal as 3 and ninitial as 4…Why?

No; the number of maxima is given by the number of radial nodes +1. The number of radial nodes is given by (n-l-1), so the number of maxima is (n-l) (i.e. en - el).

When you say "Orbitals have (n-1) nodes" and also "the number of maxima is given by the number of radial nodes +1. The number of radial nodes is given by (n-l-1)" what is the difference between those two things?

Probably best explained with an example. Take the 5d orbital. It has 5-1 = 4 nodes. It has 5-2-1 = 2 radial nodes (the other two nodes are the nodal planes that run through the nucleus). It has 2+1 = 3 maxima for each lobe of the orbital.

The question asked for the quantum numbers of the valence electrons of Ga, which are the 4s and 4p electrons. So the 0 value comes about for the 2 4s electrons.

## 33 comments:

Hi,

In class on Wednesday you talked about Homework Assignment 1, and I just wanted to clarify that this is not for marks. Also, the deadline for it is September 17th at 1:28pm, does this mean that it will not be available after that time?

Thank you!

It's not for marks, and yes, you'll be able to attempt it again after the deadline.

How do we know if our iclickers are properly registered? All it says on the website is "your iclicker serial number is... "

If you went through the process, all should be well - but even if it didn't work, the system will register your responses against your clicker serial number, and all those who haven't yet registered successfully will get another warning from me.

For us luddites without smart phones, where can we access the answers for the questions in our course pack/youtube videos of the answers? I'm not seeing them on the site...

Yeah, I don't have one either...

http://web.uvic.ca/~mcindoe/rpsc.html (it's linked from the course website under "problem solving")

Why would the electron drop from an excited state to a ground state when the element is heated? It's absorbing energy from the heat so it needs to give off energy in the form of a photon because?

Hi Caitlin

You mean like when Caleb sprayed different salt solutions into the flame? The thermal energy is enough to evaporate the solvent, convert ions to atoms, and excite some atoms into an excited state. However, this state is unstable with respect to the ground state, as it is much higher in energy, so it can fall back down to the ground state, thus emitting a photon (yellow for sodium, green for boron, etc). If you keep heating, this process keeps happening, i.e. atoms will keep being excited and keep emitting photons, as energy is being constantly introduced in the form of thermal energy. Remove the heat source, and the process will stop - there is not enough energy to promote electrons into an excited state.

Thanks

I see now that the electron first is raised to an excited energy level because it has been given thermal energy but then it drops because the excited state is unstable. This happens continuously throughout the heating process.

So the electron goes up and then down every time (and every time it goes back down a photon is emitted). This is indirectly related to any kind of preservation of energy concept (energy is given off because it has been absorbed)??

Am I on the same page as you, Professor?

Yes.

now that we've covered the entire chapter and im sufficiently brushed up and ready to attempt some practice quizzes, they're past the deadline. although i can see the questions, i cant see the answers

could you please extend them another week?

I'll talk to the course coordinator, and see what he can do.

What kind of questions should we expect to see on the first quiz?

Short questions on material from sections 1.1, 1.2, and 1.3. Nothing tricky, & you should have plenty of time - and remember, it's all open-book!

Which orbitals other than 1s are degenerate? Is 1s the only one?

There is only one 1s orbital, so degeneracy is irrelevant in this case. There p orbitals display degeneracy, which simply means that these 3 orbitals (px, py and pz) have the same energy. So do d and f orbitals (five and seven degenerate orbitals, respectively).

practice quiz 1 covers some pretty funky, unrelated junk. question 10, for instance:

The triviance of the standard laboratory nard is directly proportional to its feebity in poods and inversely proportional to its frumiance in arbols. If the units of triviance are nils, what must be the units of the proportionality constant?

but its cool, aced graded quizes 1 and 2

Do we lose marks for using hints or if we get one of our attempts wrong on the graded quiz?

The Chapter 1 questions in our notes uses the equation 1/wavelength=(Rydberg Constant)*(1/ni^2-1/n2^2) for question 4. It's not in our list of equations on our periodic table, however. Do we need to memorize that equation?

Gotta know your poods and arbols.

Don't think there are any hints in the graded quiz, but I could be wrong. Use your textbook and course notes for hints!

A very similar equation is given in the data sheet, and provided you know how wavelength and frequency are related, you can use that.

How do you know whether orbitals are degenerate or not?

They have the same energy. For your purposes, orbitals with the same value of n and l. So the three 2p orbitals are degenerate, as are the 5 3d, the 7 4f, etc. Hydrogen is exceptional in that all orbitals with the same value of n are degenerate, e.g. the 2s and 2p orbitals are the same energy. This is NOT true for multi-electron atoms, however.

should we know all the scientists and their theories for the midterm?

I thought the question on our online quiz #2 "The correct ground-state electron configuration for molybdenum is __________." was a little unfair. From the rules we've learnt, you would assume that its configuration was [Kr]5s2 4d4. I understand that for atoms (such as Cr), a more stable configuration results when a d orbital is half filled (or completely filled), therefore yielding [Kr]5s1 4d5, however, we were only told to look out for Cr and Cu.

I feel like we shouldn't really be expected to know electron configuration anomalies other than the ones taught in class or in the text.

Yes, that was slightly tricky. But it's a open book exam - if you don't know the answer, just look it up.

Two questions

1.Is there a way to relate the number of maxima to each orbital such as the nodes relate to each orbital (n-1)? Eg( how many maxima will a 4s orbital have? Or 1s?)

2.I got a different answer for this question because I used nfinal = 4 and ninitial = 2:

The electron residing in the 2p orbital of an electronically excited hydrogen atom is promoted to the 4dxy orbital by absorption of a photon light. The longest wavelength of light that can be emitted by the resulting electronically excited hydrogen atom is:

In the solutions they used nfinal as 3 and ninitial as 4…Why?

1. Yes. Orbitals have (n-1) nodes, so for example 3s, 3p and 3d orbitals all have 2 nodes (2 radial, 1 radial 1 planar, and 2 planar respectively)

2. You found a shorter wavelength. The longest wavelength will have the least energetic transition, because E = hc/lambda

But is there a way to relate the number of maxima? like in an example it said 4s level will have 4 maxima..is it just n = number of maxima?

No; the number of maxima is given by the number of radial nodes +1. The number of radial nodes is given by (n-l-1), so the number of maxima is (n-l) (i.e. en - el).

When you say "Orbitals have (n-1) nodes" and also "the number of maxima is given by the number of radial nodes +1. The number of radial nodes is given by (n-l-1)" what is the difference between those two things?

Probably best explained with an example. Take the 5d orbital. It has 5-1 = 4 nodes. It has 5-2-1 = 2 radial nodes (the other two nodes are the nodal planes that run through the nucleus). It has 2+1 = 3 maxima for each lobe of the orbital.

On our first midterm you asked as for the three sets of quantum numbers. Could you explain how Gallium has a 0 for the angular momentum number?

The question asked for the quantum numbers of the valence electrons of Ga, which are the 4s and 4p electrons. So the 0 value comes about for the 2 4s electrons.

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