Per Business Insider[0], Argon and Carbon were part of an alphabetical lineup:

> An internal document shows that Google has tested a series of Gemini 4 models, internally named Argon, Barium, and Carbon.

Then I suppose they tacked on Hydrogen since it's supposed to be a "light" model and hydrogen is the lightest element. I agree that it's super confusing though.

[0] https://www.businessinsider.com/google-employees-test-new-ge...