Chem question- in which subshell are the valence electrons found?

[diene]

As I was doing Chad's Chemistry quizzes, I came across this question:
"Which of the following is a possible set of quantum numbers [n,l,ml,ms] for a valence electron in bromine?

I don't have a problem with doing question, but in the explanation it stated this: "The 4s and 4p electrons are considered the 7 valence electrons of Br."
Why is it not 4p and 3d? What's the general rule for determining which subshell the valence electrons are located for each element?
Thanks!

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[rockclock]

As I was doing Chad's Chemistry quizzes, I came across this question:
"Which of the following is a possible set of quantum numbers [n,l,ml,ms] for a valence electron in bromine?

I don't have a problem with doing question, but in the explanation it stated this: "The 4s and 4p electrons are considered the 7 valence electrons of Br."
Why is it not 4p and 3d? What's the general rule for determining which subshell the valence electrons are located for each element?
Thanks!

everything with the highest n (at least for main group elements...transition metals are trickier)

 

[needzmoar]

As I was doing Chad's Chemistry quizzes, I came across this question:
"Which of the following is a possible set of quantum numbers [n,l,ml,ms] for a valence electron in bromine?

I don't have a problem with doing question, but in the explanation it stated this: "The 4s and 4p electrons are considered the 7 valence electrons of Br."
Why is it not 4p and 3d? What's the general rule for determining which subshell the valence electrons are located for each element?
Thanks!

Well if you're dealing with complexes involving transition metals, then D shell electrons (of the metal) are considered valence electrons too. For main group representative elements (elements of S and P blocks) the S and P orbitals.

 

[needzmoar]

everything with the highest n (at least for main group elements...transition metals are trickier)

you beat me to it >O

 

[mh0000]

everything with the highest n (at least for main group elements...transition metals are trickier)

^^ What this genius said. Valence electrons are those accessible and participate in chemical reactions. For Br, the 3d shell is full, so will not usually participate. This is generally true for main-group elements, that is the inner d subshell is not usually included as a valent shell. Like rockclock said, transition elements are different because the d subshell electrons usually do participate in bonding and chemical reactions.

 

[rockclock]

mh and needz have pretty much already filled in the details, but this is a nice little paragraph if you want it all in one package:

http://en.wikipedia.org/wiki/Valence_electron#Valence_electrons_and_electron_configuration

 

[diene]

You guys are fast! Thank you soo much!

So based one what you guys mentioned, if I wanted to figure out the location of valence electrons for Cr, would it be 3d and 4s? and for Zn? would it be 3p and 4s, since 3d is full?

 

[needzmoar]

You guys are fast! Thank you soo much!

So based one what you guys mentioned, if I wanted to figure out the location of valence electrons for Cr, would it be 3d and 4s? and for Zn? would it be 3p and 4s, since 3d is full?

Yes and sorta yes. Zinc does not have any P electrons

I'm actually glad you mentioned chromium. Make sure you know the exception to chromium group atoms and copper group atoms.

example: the valence electron configuration for Cr would be
4s1 3d5

NOT
4S2 3d4

this is to minimize repulsion between electrons

 

[rockclock]

You guys are fast! Thank you soo much!

So based one what you guys mentioned, if I wanted to figure out the location of valence electrons for Cr, would it be 3d and 4s? and for Zn? would it be 3p and 4s, since 3d is full?

the easiest thing to do is:
1) for main group elements, count the the s-block and p-block past the last noble gas
2) for transition metals, count everything past the last noble gas

 

[diene]

Yes and sorta yes. Zinc does not have any P electrons

I'm actually glad you mentioned chromium. Make sure you know the exception to chromium group atoms and copper group atoms.

example: the valence electron configuration for Cr would be
4s1 3d5

NOT
4S2 3d4

this is to minimize repulsion between electrons

The electron configuration of Zn is: 1s22s22p63s23p64s23d10... so it does have p electrons? but they are just not valence? and thanks for the reminded about the exception😀

the easiest thing to do is:
1) for main group elements, count the the s-block and p-block past the last noble gas
2) for transition metals, count everything past the last noble gas

gotcha, but what if d is full? then the valence electrons cannot be found there correct?

 

[needzmoar]

The electron configuration of Zn is: 1s22s22p63s23p64s23d10... so it does have p electrons? but they are just not valence? and thanks for the reminded about the exception😀
sorry, I meant no P valence electrons.

 

[rockclock]

The electron configuration of Zn is: 1s2 2s2 2p6 3s2 3p6 4s2 3d10... so it does have p electrons? but they are just not valence? and thanks for the reminded about the exception😀


gotcha, but what if d is full? then the valence electrons cannot be found there correct?

for the love of god, use spaces man!

correct. e.g. zinc has two valence electrons because a complete 3d10 is considered part of the core. haha I guess it's not as straightforward as it sounds...honestly, after a while you just get used to finding an element on the periodic table and knowing how many valence it has. spelling it out in all these rules makes it sound more complicated than it really is...

 

[diene]

for the love of god, use spaces man!

correct. e.g. zinc has two valence electrons because a complete 3d10 is considered part of the core. haha I guess it's not as straightforward as it sounds...honestly, after a while you just get used to finding an element on the periodic table and knowing how many valence it has. spelling it out in all these rules makes it sound more complicated than it really is...

lol sorry about that. Thanks for all your help!