Unintuituve naming convention: para- denotes antiparallell?

In summary, the naming convention for orthohelium and parahelium, which refer to the spin of the electrons in a helium atom, is unintuitive as "para-" denotes antiparallel instead of parallel. This convention is based on historical reasons, as "para" means "next to" or "beyond" in Latin, but it has caused confusion and is not commonly used in the scientific community. The general terms for this concept are singlet and triplet.
  • #1
phz
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Unintuituve naming convention: "para-" denotes antiparallell?

I did a project a week ago that required studies of the helium atom. Depending on if the two electrons spin are parallell or anti-parallell it is referred to as orthohelium (parallell) or parahelium (antiparallell).

Intuitively I would have imagined the naming convention the other way round: parahelium for parallell spins.

Today I "corrected" a professor in subatomic physics when positronium came up which apparently has the same naming convention. My thoughts are along the line: "if even HE finds it unintuitive, why is it so?" :-) Is it something else that is parallell/orthogonal, or is it just historic reasons?

Google didn't help me.
 
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  • #2


It is for historical reasons. Para means "next to" or "beyond" in latin (and ortho means straight), as in paranormal.
It is presumably because this was orignally the names of lines in the spectrum of helium There are lots of other examples of this, the "d" in e.g. 2d orbitals is short for "diffuse" (as in a diffuse line on the photographic plate used to capture the spectrum).
 
  • #3


It's also just a historic thing for helium. The general terms are singlet/triplet.
In fact, I'd recommend against using the 'ortho/para helium' terminology; it can only cause confusion really.
 

1. What does "para-" mean in this naming convention?

In this context, "para-" is a prefix that indicates "antiparallel." This means that the object or concept being described is in the opposite direction or orientation to something else.

2. Why is "para-" used instead of a more intuitive term?

The use of "para-" in this naming convention is to maintain consistency with other scientific terms and notations. It is also used to avoid confusion with similar terms that may have different meanings in other scientific fields.

3. Does this naming convention have any historical significance?

Yes, the use of "para-" to indicate antiparallel is derived from the Greek prefix "para-" which means "beside" or "alongside." This prefix has been widely used in scientific literature for many years.

4. How does this naming convention apply to scientific research?

This naming convention is commonly used in fields such as physics, biology, and chemistry to describe the orientation or direction of objects or molecules. It allows for clear and concise communication among scientists and helps to avoid confusion when discussing complex concepts.

5. Are there any exceptions to this naming convention?

While "para-" typically denotes antiparallel, there may be instances where it is used to indicate a different concept, depending on the specific field of study. It is important to always consider the context and consult with other scientists to ensure accurate understanding and usage of this naming convention.

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