How do you add more than one name tag for a Radio button?

I have the following code.

10:00 - 10:30:  <input type="radio" name="group1" value="Science"> Science <input type="radio" name="group1" value="Math"> Math<br>
10:30 - 11:00:  <input type="radio" name="group2" value="Science"> Science <input type="radio" name="group2" value="Math"> Math<br>

So how can I make it where if someone presses Science for the first time then they can't click it again for the second?