Principal quantum number

The principal quantum number is a number that tells scientists how energy levels are arranged in an atom. It's kind of like how a group of people get in line when they're at school. The principal quantum number is like the person at the front of the line who decides who goes first. When scientists are looking at an atom's energy levels, the principal quantum number tells them which electrons are closer to the nucleus, or middle part, of the atom. This is why it's so important for scientists to know about the principal quantum number.