Which of these elements can't have an expanded octet in a Lewis structure?

P,O,Br,N,S,C,B,Si

I think its O,C,B,N. Are elements that don't have a d oribial arent supposed to be included?

We usually count those element that don't have d orbitals as not being able to expand the octet.

So then it would be all of them except Br right?

Don't P and S have expanded octets?

For example SF6 and PF5.

Here is something I found that may prove useful.

http://72.14.205.104/search?q=cache:eeDUwaZtsE8J:student.ccbcmd.edu/~cyau1/ExpandedOctet.pdf+expanded+octet&hl=en&ct=clnk&cd=1&gl=us&ie=UTF-8

In my first response, I believe I was thinking of hybridization. Atoms with no d orbitals can form s and p hybrids but not s, p, and d hybrids (since no d orbitals are there.)

I know I was and that is correct. An expanded octet cannot occur with atoms less than atomic number 10 (neon) because there are no d orbitals. So you are correct; I believe Br is the only one with an atomic number larger than 10. I brought up P and S but those elements ARE greater than 10 AND since they are in the third period, they contain 3d orbitals and extra electrons can fit around them. Therefore, my first response was ok; d orbitals are necessary for hybridization to take place (involving d, s, and p orbitals) AND d orbitals are necessary to accommodate and expanded octet. I hope this helps.

To determine which elements can't have an expanded octet in a Lewis structure, we need to consider a few factors.

1. Elements with an "s" or "p" block electron configuration can form expanded octets, whereas elements with a "d" or "f" block electron configuration typically do not.

2. The octet rule states that most atoms tend to gain, lose, or share electrons in order to achieve a stable configuration with eight valence electrons. However, there are exceptions to the octet rule when forming molecules involving elements from the third period and beyond in the periodic table. These exceptions allow atoms to have more than eight electrons in their valence shell.

Now, let's analyze the elements you mentioned:

- Oxygen (O): Oxygen typically obeys the octet rule and forms two single bonds to achieve a stable configuration with eight valence electrons. Oxygen usually doesn't form an expanded octet in a Lewis structure.
- Carbon (C): Carbon typically obeys the octet rule and forms four single bonds to achieve a stable configuration with eight valence electrons. Carbon usually doesn't form an expanded octet in a Lewis structure.
- Boron (B): Boron usually undergoes incomplete octets, meaning it typically forms less than eight valence electrons. Therefore, it doesn't typically have an expanded octet.
- Nitrogen (N): Nitrogen typically obeys the octet rule and forms three single bonds (or a triple bond) to achieve a stable configuration with eight valence electrons. Nitrogen typically doesn't form an expanded octet in a Lewis structure.
- Phosphorus (P): Phosphorus is an example of an element that can form an expanded octet. It is in the third period and can accommodate additional electrons in its valence shell beyond the octet.
- Sulfur (S) and Silicon (Si): Both sulfur and silicon can form expanded octets. They are also in the third period and can accommodate more than eight electrons in their valence shells.

So, based on this analysis, the elements that cannot have an expanded octet in a Lewis structure are Oxygen (O), Carbon (C), Boron (B), and Nitrogen (N).