If your employer sends you home due to circumstances outside of your control such as due to weather, does your employer have to pay you for the time you are lacking?

It depends. Are you an exempt employee or a nonexempt employee? If you don't know, what exactly are your job duties? And it may also depend on the reason. I could see where possibly "weather" could be different from "the electricity went out". Need more details.

Non-exempt. The electricity went out due to the weather. We were told that another storm front was going to come through that was stronger, so we were told that due the electricity being out and another front coming through we were being sent home.

The weather was outside your employer's control as well. No, they do not have to pay you for the balance of the day.

Electricity was still on in other parts of the building, so the entire building was not sent home. Even in this case they do not have to pay?

No, they don't. Legally, they wouldn't have to pay nonexempt employees if they sent you home because they didn't like the color of your socks. Plus, if the electricity was off in your part of the building, then you couldn't work, right? The people in the part of the building whose electricity was still on could work.