[Watermelon]

Valence electrons are apparently the electrons in the outermost shell.
Maximum number of valence electron in shells:
K - 2
L - 8
M - 18
N - 32

Neutral calcium atom has 20 electrons.
2 in the K shell. (2)
8 in the L shell. (10)
10 in the M shell. (20)

Therefore, Calcium should have 10 valence electrons. But it has 2. Why. Can anyone please help?

Well, if I look at subshells, it would explain it... because there would be 2 electrons in the outermost subshell.
But I don't think valence electrons are the electrons in the outermost subshell.. I don't know

If I look at Chlorine with 17 electrons..

1s² 2s² 2p⁶ 3s² 3p⁵ which is 17 electrons.. then it should have 5 valence electrons since theres 5 in the outermost subshell, but it has 7 according to the entire internet, which would mean valence electrons are the ones in the outermost shell.

But my two findings contradict each other. Somethings wrong..

Can anyone please help me out?

[ramboacid]

Valence electrons are electrons in the outermost energy level, which is also the outermost shell.

When you are looking at an electron configuration, let's say the one for chlorine, the letters represent the subshell, or the shape of the orbitals. The numbers in front of the letters represent the energy level of the subshell. So for chlorine, we can see that it has electrons in three energy levels by looking at its electron configuration.

Since valence electrons are electrons in the outermost energy level, all you have to do is determine the outermost energy level and then count the number of electrons in it.

For chlorine, the outermost energy level is 3, so we just count the electrons in all the orbitals preceded by the number 3. There are 2 in the 3s orbital and 5 in the 3p orbitals, giving a total of 7 valence electrons.

For calcium, if you wrote out the electron configuration, the highest energy level would be 4, and the only occupied orbital in the 4th energy level would be the 4s orbital. Since there are 2 electrons in the 4s orbital and none in the 4p orbitals, there are only 2 electrons in the entire 4th energy level. Therefore, there are 2 valence electrons in calcium.

[Watermelon]

Valence electrons are electrons in the outermost energy level, which is also the outermost shell.

When you are looking at an electron configuration, let's say the one for chlorine, the letters represent the subshell, or the shape of the orbitals. The numbers in front of the letters represent the energy level of the subshell. So for chlorine, we can see that it has electrons in three energy levels by looking at its electron configuration.

Since valence electrons are electrons in the outermost energy level, all you have to do is determine the outermost energy level and then count the number of electrons in it.

For chlorine, the outermost energy level is 3, so we just count the electrons in all the orbitals preceded by the number 3. There are 2 in the 3s orbital and 5 in the 3p orbitals, giving a total of 7 valence electrons.

For calcium, if you wrote out the electron configuration, the highest energy level would be 4, and the only occupied orbital in the 4th energy level would be the 4s orbital. Since there are 2 electrons in the 4s orbital and none in the 4p orbitals, there are only 2 electrons in the entire 4th energy level. Therefore, there are 2 valence electrons in calcium.

thank you so much

[Clovermite]

I apologize for resurrecting such an old thread, but my question is exactly the same as the OP, and I still feel like I need further clarification. I figured it would be better than posting the exact same question in a new thread.

How does Calcium end up with electrons in the 4s orbital? Every time I try to write it out, I end up with 2 electrons in the 3d orbital instead.

As I understand it, the first energy level has only the s subshell (with 2 electrons). The second energy level has the s subshell, and the p subshell (with 6 electrons). Together, that's eight electrons in the second shell, and a total of 10 when you combine with the first energy level. Unless I'm misunderstanding something, the third energy level has the s subshell, p subshell, and the d subshell (with 10 electrons). Togeterh that would make for 18 electrons in the third leven, and a total of 28 electrons in the first three shells.

Therefore, with twenty electrons, I would expect:

1s - 2 electrons (total of 2)
2s - 2 electrons (total of 4)
2p - 6 electrons (total of 10)
3s - 2 electrons (total of 12)
3p - 6 electrons (total of 18)
3d - 2 electrons (total of 20)

It seems like we would need 10 more electrons to complete the third energy level and leave two remaining electrons in the fourth energy level.

Googling around, I can see that for Strontium (the next element in the same column) the third energy level DOES have a d subshell capable of holding 10 electrons. But then we see the same skipping of the d subshell in the 4th level to deposit 2 electrons in the 5th level. (https://answers.yahoo.com/question/index?qid=20080528083940AAmc0Q0)

Why do we skip the d subshell to deposit electrons on the next level's s subshell? At what point do we start filling up the d subshell for a level?

[dk_ch]

I apologize for resurrecting such an old thread, but my question is exactly the same as the OP, and I still feel like I need further clarification. I figured it would be better than posting the exact same question in a new thread.

How does Calcium end up with electrons in the 4s orbital? Every time I try to write it out, I end up with 2 electrons in the 3d orbital instead.

As I understand it, the first energy level has only the s subshell (with 2 electrons). The second energy level has the s subshell, and the p subshell (with 6 electrons). Together, that's eight electrons in the second shell, and a total of 10 when you combine with the first energy level. Unless I'm misunderstanding something, the third energy level has the s subshell, p subshell, and the d subshell (with 10 electrons). Togeterh that would make for 18 electrons in the third leven, and a total of 28 electrons in the first three shells.

Therefore, with twenty electrons, I would expect:

1s - 2 electrons (total of 2)
2s - 2 electrons (total of 4)
2p - 6 electrons (total of 10)
3s - 2 electrons (total of 12)
3p - 6 electrons (total of 18)
3d - 2 electrons (total of 20)

It seems like we would need 10 more electrons to complete the third energy level and leave two remaining electrons in the fourth energy level.

Googling around, I can see that for Strontium (the next element in the same column) the third energy level DOES have a d subshell capable of holding 10 electrons. But then we see the same skipping of the d subshell in the 4th level to deposit 2 electrons in the 5th level. (https://answers.yahoo.com/question/index?qid=20080528083940AAmc0Q0)

Why do we skip the d subshell to deposit electrons on the next level's s subshell? At what point do we start filling up the d subshell for a level?

The last sub shell would be 4s instead of 3d as the former has less energy than the later. 4s has got n+l value 4+0=4 and 3d has n+l value 3+2 =5.

[Borek]

Why do we skip the d subshell to deposit electrons on the next level's s subshell?

http://en.wikipedia.org/wiki/Aufbau_principle

[Clovermite]

Thank you Borek.

Sorry I meant to respond earlier, I just felt really embarassed. When I read your post, I remembered seeing the principle named in my textbook, but I'd thought that it hadn't explained. When I looked more carefully, I saw that it did detail the answers to my questions, it had just done so with a long string of "less than" symbols that I had been inadvertently skipping over because I assumed that they would also explain in text rather than just via formula.

I will be more thorough in reading through my text book from now on.