Octet Rule: Why the Confusion?

  • Thread starter repugno
  • Start date
  • Tags
    Confusion
In summary, the conversation discusses the confusion surrounding the number of electrons allowed in a shell and how it relates to the Octet rule. The conversation also delves into the aufbau process and how electrons fill up subshells in a specific order. The element Copper is used as an example to illustrate the concept of the Hund's rule, which states that half-filled and filled sub-levels have unusual stability. Examples of electron configurations for different elements are also provided to further explain these principles.
  • #1
repugno
78
0
Something is confusing me again. In one of my textbooks it clearly states that: generally there are only a certain number of electrons which are allowed in a shell.

1st:2 2nd:8 3rd:8 etc …

I believe this is known as the octet rule.

If I move on to my other textbook it states that the 3rd shell can now hold 18 electrons.
Are they trying to confuse me or is there a reasonable explanation to this?
 
Chemistry news on Phys.org
  • #2
:) here is the explanation::

Subshell electron capacities:

Code:
s  2
p  6
d  10
f  14

s+p+d = 18
 
  • #3
Just remember the aufbau process, the way the electron shells are actually filled up:

Code:
1s  
2s  2p  
3s  3p  3d
4s  4p  4d  4f
5s  5p  5d  5f
6s  6p  6d
7s  7p
Draw a 45° angle from NE to SW, so that the shells are filled: 1s, 2s, 2p, 3s, 3p, 4s etc.
 
  • #4
Thanks for the reply. :)
It makes a bit more sense now, so when 4s is filled, 3d starts filling. Another problem, why is it that Cu has only one electron in 4s but a full shell of 3d?
 
  • #5
Originally posted by repugno
Thanks for the reply. :)
It makes a bit more sense now, so when 4s is filled, 3d starts filling.
No, I don't think so. The second textbook example you gave just says that the first three subshells can hold 18 electrons. But when you look at the aufbau process that I posted, you will see that that an electron will go to 4s before it goes to 3d.


Another problem, why is it that Cu has only one electron in 4s but a full shell of 3d?
Like I just said , again look at the aufbau process, this is how the subshells are filled::

1s, 2s, 2p, 3s, 3p, 4s, 3d that helps?
 
  • #6
Originally posted by Monique


Like I just said , again look at the aufbau process, this is how the subshells are filled::

1s, 2s, 2p, 3s, 3p, 4s, 3d that helps? [/B]

You have successfully made me understand the aufbau principle, thank you very much.:smile:
Now, when I look at my textbook it shows a table with the electron configurations of the first 36 elements in terms of the subshells. If I look at copper there is inconsistency.

Cu

1s22s22p63s23p64s13d10

If 4s fills before 3d, then why has 4s only got one electron given that, to fill an “s” subshell there must be two electrons in it?, and here the 3d subshell is completely filled.
 
  • #7
Very interesting and well noted!

There is actually something called the Hund's rule: half filled and filled sub-levels have unusual stability.

In fact, the 4s subshell is only slightly lower in energy than the 3d one. So the stabilization that it gets by either half filling or filling the higher subshell is greater than the energy necessary to take the electron out of 4s..

Here are a few other examples::

Code:
Cr = 1s2   2s2   2p6 3s2   3p6   4s1 3d5
Cu = 1s2   2s2   2p6 3s2   3p6   4s1 3d10 
Ta = 1s2   2s2   2p6 3s2   3p6   4s2 3d10 4p6   5s1 4d4 
Pd = 1s2   2s2   2p6 3s2   3p6   4s2 3d10 4p6   5s0 4d10
 
Last edited:

1. What is the octet rule?

The octet rule is a basic principle in chemistry that states that atoms tend to gain, lose, or share electrons in order to achieve a stable electron configuration with 8 valence electrons, similar to that of noble gases.

2. Why is there confusion surrounding the octet rule?

There is confusion surrounding the octet rule because it is a simplified model that does not always accurately describe the behavior of atoms in molecules. Some atoms, such as those in the third period or beyond, can have more than 8 valence electrons and still be stable.

3. How does the octet rule apply to covalent bonding?

In covalent bonding, atoms share electrons in order to achieve a stable electron configuration. The octet rule can help predict the number of bonds an atom will form based on how many valence electrons it needs to gain or lose to reach 8.

4. What is the difference between the octet rule and the duet rule?

The octet rule applies to atoms in the second period or beyond, while the duet rule applies to atoms in the first period. The duet rule states that these atoms tend to gain, lose, or share electrons in order to achieve a stable electron configuration with 2 valence electrons.

5. Can the octet rule be broken?

Yes, the octet rule can be broken in some cases. For example, atoms with an odd number of valence electrons or atoms with more than 8 valence electrons can still form stable compounds through the sharing or transfer of electrons. Additionally, atoms in certain compounds may have incomplete octets and still be stable.

Similar threads

Replies
7
Views
3K
Replies
5
Views
2K
Replies
13
Views
10K
  • Introductory Physics Homework Help
Replies
23
Views
286
  • Feedback and Announcements
Replies
25
Views
2K
Replies
9
Views
4K
Replies
10
Views
937
  • Thermodynamics
Replies
7
Views
1K
  • Atomic and Condensed Matter
Replies
5
Views
4K
Back
Top