## Tips for Subshells

alex_4l
Posts: 109
Joined: Thu Sep 26, 2019 12:18 am

### Tips for Subshells

In class, we had a problem where wrote out the electron configuration for Calcium. Instead of doing the whole electron configuration, we wrote
[Ar] 4s^2. A few people next to me were confused about this so I thought I'd explain why. This method is a sort of shortcut for writing out electron configurations, our professor might specify when to use this method and when he wants the whole thing written out, but it's helpful to know both ways just in case. Looking at Calcium, it's in the 4th period of the periodic table. In order to use the shortcut, you would jump up to the 3rd period which is one above it and look at the noble gas that comes right before it, in this case it would be Argon. With the shortcut, you HAVE to use a noble gas, this is the only way it works. After stating argon, you would write the next few configurations to get to Calcium, which would be 4s^2. Basically, you have to state the core electron first (a noble gas since it has 8 electrons and no valence ones), then the valence electrons after that. By stating Argon first, you're basically saying that this element has the configuration leading up to Argon and stating the 4s^2 is depicting Calcium's placement.
Hope this helps anyone!

Amina Durrani 3G
Posts: 52
Joined: Sat Jul 20, 2019 12:16 am

### Re: Tips for Subshells

Wait, why can you only use a noble gas again? I’m little confused.

alex_4l
Posts: 109
Joined: Thu Sep 26, 2019 12:18 am

### Re: Tips for Subshells

This is a table I've used in the past that sort of explains subshell letters in correlation to electron shells, it's super simple but I hope this helps!

Shell # of Subshells Letters Specifying Subshells

n=4 4 s, p, d, f
n=3 3 s, p , d
n=2 2 s, p
n=1 1 s

alex_4l
Posts: 109
Joined: Thu Sep 26, 2019 12:18 am

### Re: Tips for Subshells

Amina Durrani 3G wrote:Wait, why can you only use a noble gas again? I’m little confused.

It's because those are the only elements on the periodic table that have a complete shell with no valence electrons on the end, so they are the core electron used!

preyasikumar_2L
Posts: 101
Joined: Fri Aug 09, 2019 12:17 am

### Re: Tips for Subshells

You use the noble gas from the period above the element you're writing the electron configuration for because noble gases have a full octet of electrons, and so the remaining electrons of the element you're configuring would be valence electrons. Noble gases have a full octet of electrons, so the noble gas configuration condenses the full electron configuration such that the most relevant information about the valence electrons of that element is provided. The noble gas is substituted to represent all of the electrons that aren't valence electrons.