gchem/math q's

[113zami]

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1) According to Aufbau, the lowest energy orbitals fill first, that's why 4s fills before 3d because when you apply the n+L rule to both , for 4s you get 4 and for 3d you get 6, which implies that 4s has lower energy than 3d.

but there is also a rule that says the energy of the electron is directly proportional to the principle energy level 👎 so the higher the n the higher the energy of the electron, so shouldn't 4s have higher energy the 3d? and to prove it, for example, if you want to ionize Ti you start by removing the high energy electrons first, that is, you start removing electrons from the 4s orbital first before the 3d which implies that 4s has higher enegy than 3d,
so can anyone please clarify which has higher energy 4s or 3d, because it seems like the two rules contradict eachother.


2) What's the wavelength (in nm) if the energy of the electron is 3.03x10^(-19)J ? Ansr: 656nm
Using this equation E=(hc)/wavelength which rearranges to

Wavelength =(hc)/E

=((6.626x10^(-34) J.s)(3x10^(8)m/s))/ 3.03x10^(-19)J
=6.56x10^(-7)m
Converting that to nm:
6.56x10^(-7)m(10^(-9)nm/1m)= 6.56x10^(-16)nm……..which is not the correct ansr what am I doing wrong???

3) This is a math question but I need it for a pH problem, how can you do it without a calculator?
10^(.65)=?
Ansr=4.46

appreciate any help😳

 

[Streetwolf]

3) This is a math question but I need it for a pH problem, how can you do it without a calculator?
10^(.65)=?
Ansr=4.46

That's about 10^(2/3) which is the cube root of 100 which is between 4 and 5 (between cube root of 64 and cube root of 125).

Yeah you'll just have to guess at that point. I'd just go around 4.5. I'm sure if you had some answer choices that they wouldn't be close. You might have choices like:

A. 3.25
B. 4.46
C. 5.88
D. 7.02
E. 8.39

You get the picture. They'll spread them out. If you think about it the way I did, you'll narrow it down significantly and almost certainly to one answer. In this case it's highly unlikely that it's anything NOT in the 4.00-4.99 range.

 

[113zami]

thanks streetwolf,
can someone please help me with the other questions, its bothering me so much cuz its basic stuff and i am still having confusions

 

[Streetwolf]

1. I may be wrong but I think the 2nd rule applies to cases where the 1st rule needs a 'tie breaker'. Actually 3d = 5 because s = 0, p = 1, and d = 2. If you looked at 4p you'd also get 5 (4 + 1) so which one is higher? Well, 4 > 3 so 4p > 3d.

3d > 4s but 4s is taken off first I *think* because it is farther from the nucleus.

Again it's been a while so someone correct me if I'm wrong.

2. There are 10^9 nm / 1 m, not -9.

 

[113zami]

Ok sw, so if for example a question says, which has higher energy, an electron near the nucleus or an electron farther away from the nucleus? if the n and L are not given, which answer would you choose? or is it impossible to tell without the n and L values?
unless n and L are given, I would just go by the 2nd rule and say the farther the higher the energy, then if n and L are given the ansr might change accordingly, am I right??