# periodic table question

I swear!Registered User regular
I've been trying to help my daughter study for her chemistry test tomorrow and she was reviewing a quiz from earlier this year where she got this question wrong:

(I'm paraphrasing based on my poor memory) The third principal energy level of an atom can contain...
a. The s and p orbitals only
b. The s, p, and d orbitals only

My daughter chose a. but the teacher said it was b.

She says the reason she chose a. was because she looked at the third period of the table and saw that the elements there are still only using the s and p orbitals.

I explained that I think she got it wrong because she confused the period with the energy level. The third energy level starts in the third period, but doesn't take on electrons in the d orbital until you get past calcium which is in the forth period.

Is my assessment correct?

@3cl1ps3 you know chemistry, right?

"Simple, real stupidity beats artificial intelligence every time." -Mustrum Ridcully in Terry Pratchett's Hogfather p. 142 (HarperPrism 1996)

## Posts

• I will build a labyrinth to house the cheese Registered User regular
edited December 2023
I've been trying to help my daughter study for her chemistry test tomorrow and she was reviewing a quiz from earlier this year where she got this question wrong:

(I'm paraphrasing based on my poor memory) The third principal energy level of an atom can contain...
a. The s and p orbitals only
b. The s, p, and d orbitals only

My daughter chose a. but the teacher said it was b.

She says the reason she chose a. was because she looked at the third period of the table and saw that the elements there are still only using the s and p orbitals.

I explained that I think she got it wrong because she confused the period with the energy level. The third energy level starts in the third period, but doesn't take on electrons in the d orbital until you get past calcium which is in the forth period.

Is my assessment correct?

@3cl1ps3 you know chemistry, right?

Your explanation is more or less correct, certainly for the level your daughter needs to know it at. Principal energy level and period aren't the same. Principal energy level is referring to which level of the electron shell you're considering, period is thinking about how many electrons are in the outermost level i.e. valence number (more or less - it gets more nuanced once you get into d and f elements). So the answer is indeed b as the third principal energy level is when you start to see d-orbitals forming.

3cl1ps3 on
• I swear! Registered User regular
Phew! I really started doubting myself because I didn't even remember the period numbers from when I took chemistry years ago.

"Simple, real stupidity beats artificial intelligence every time." -Mustrum Ridcully in Terry Pratchett's Hogfather p. 142 (HarperPrism 1996)
• DelawareRegistered User regular
The way I remembered it was that you could have the d-orbital shell but it can be empty because you have to fill up s and p first. I like her deductive reasoning though.

• I swear! Registered User regular
Good news! She got an A on her exam! Thanks for the help.

"Simple, real stupidity beats artificial intelligence every time." -Mustrum Ridcully in Terry Pratchett's Hogfather p. 142 (HarperPrism 1996)