Comments on: How Do We Know Methane (CH4) Is Tetrahedral?

By: James Ashenhurst

James Ashenhurst — Tue, 21 Oct 2025 15:56:30 +0000

In reply to Dejan Jasovic. Yes, that's what's in the diagram under 2)

By: James Ashenhurst

James Ashenhurst — Tue, 21 Oct 2025 15:55:57 +0000

In reply to amalie. Great point. I changed the image and renamed them as "inner shell" electrons.

By: James Ashenhurst

James Ashenhurst — Tue, 19 Dec 2023 12:32:17 +0000

In reply to Anonymous. Thank you for the helpful comment!

By: Anonymous

Anonymous — Wed, 13 Dec 2023 20:39:31 +0000

Just a small nitpicking point: I believe that in the first (incorrect) model of methane with the 3 “p orbital bonds” along the x, y, z axes, in order to minimize repulsion the remaining “s orbital bond” should really be pointing in the (-1, -1, -1) direction as opposed to the (-1, -1, 0) direction, in which case the H-C-H bond angle would actually be about 125.3 degrees, or 180 degrees minus the magic angle: https://en.wikipedia.org/wiki/Magic_angle.

By: amalie

amalie — Tue, 31 May 2022 06:47:19 +0000

In the first figure under 1. , how come the two 1s electrons are called “1s valence shell electrons” if they are in the inner shell and are not available for bonding? Does valence shell electron = outer shell electron that is available for bonding?

By: James Ashenhurst

James Ashenhurst — Wed, 26 Jan 2022 04:04:20 +0000

In reply to F. E. Ziegler. Thank you very much. I have benefitted from your site for years.

By: F. E. Ziegler

F. E. Ziegler — Fri, 07 Jan 2022 15:27:23 +0000

See a Brief History of Organic Chemistry here (slides 35 and 36): http://ursula.chem.yale.edu/~chem220/chem220js/StudyAids.html#History
If memory serves me correctly, A. W. Hofmann was giving this lecture about the time that Lee was surrendering to Grant in 1865.

By: Dejan Jasovic

Dejan Jasovic — Tue, 28 Sep 2021 04:07:30 +0000

In 2. where we try to figure out the structure of methane, it is said that the 2 electrons in 1s^2 are not available for bonding. So then how did we come up with the assumption that there would be 3p shells with 1 electron in each and 1 S shell? Shouldn’t we expect to see 2s^2 shell with 2 electrons and 2p shells with 1 electron in each? Where did the extra electron come from?

By: James Ashenhurst

James Ashenhurst — Mon, 01 Jul 2019 12:16:23 +0000

In reply to Rafael. This is a very good point. A square planar carbon with 4 different substituents can actually have *three* isomers (try it), all stereoisomers but none of them enantiomers.

By: Rafael

Rafael — Fri, 21 Jun 2019 23:18:29 +0000

I believe that the idea of a square planar carbon with 4 different substiuents having only one isomer is not accurate. Yes, the mirror image is the same as the original, but switching two substituents would provide a different isomer.
A square planar geometry, however, would make dichloromethane and similar molecules exist as 2 isomers (cis and trans), and would also increase the number of possible isomers for molecules with more than 1 stereochemical centers, breaking the 2^n rule.
As a sidenote, I want to say that I’ve been using this website since 2014 and I think it’s amazing, so thank you for the dedication.