So... for the element of CHLORINE, you already know that the atomic number tells you the number of electrons. That means there are 17 electrons in a chlorine atom. Looking at the picture, you can see there are two electrons in shell one, eight in shell two, and seven in shell three.
If 1/2 an hour only used up 1/9 of her battery, 9, 1/2 would give us 9/2, which if you simplified it gets you 8 1/2 hours. Hope this helps! Have a great day!
