1
An electron has a negative charge.
To express this scientific fact, start by signing 'electron' to establish the subject. Then, follow up with the signs for 'negative' and 'charge' to describe the particle's fundamental property.
2
The atom has one electron.
Begin by signing 'atom' to set the context, then sign 'have' and 'one'. Finish with the sign for 'electron' to clearly state the composition of the atom.
3
Electrons orbit the nucleus.
You can sign 'electron' and emphasize the circular orbiting motion around your stationary non-dominant hand. The movement itself naturally conveys the concept of orbiting the nucleus.