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I am a 11th/12th grade student studying orbital configurations. I have gone over this lesson and it says to always draw spin up first. However, it never says why. Is drawing down spins first incorrect?

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    $\begingroup$ There is definitely no physical reason behind this. Or, for that matter, behind the very idea of drawing spins up/down, rather than left/right. $\endgroup$ – Ivan Neretin Aug 21 '19 at 15:53
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    $\begingroup$ By doing it consistently, you are sort-of automatically following Hund's Rule. But it makes more sense to learn the rule itself and follow it consciously. $\endgroup$ – TAR86 Aug 21 '19 at 19:34
  • $\begingroup$ Consistency is just a good habit to get into so that you don't forget to follow Hund's Rule. I would gather that up is typically drawn first because it's easier to draw an up arrow vs a down arrow. If a down arrow is faster/easier for you, go for it. $\endgroup$ – Melanie Shebel Aug 21 '19 at 19:43
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    $\begingroup$ And there was at least 2 more already - one of them also in "related" , just right from my comments... $\endgroup$ – Mithoron Aug 21 '19 at 22:34
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There is no real reason about that and drawing them "down" would be exactly the same as long as you draw them always in the same direction (it needs to be consistent).

The same applies to orbital lobes which can be hollow (white) or plain black depending on their relative sign. When two molecules' orbitals interact, you just consider they have the right sign for an interaction.

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