Biology/Chemistry: Atoms and isotopes?

Question

I have several questions but first I will give the background then ask the questions. I'm studying my biology book before college starts so I can try to get a better grasp on the concepts, so I don't have a teacher at the moment. Maybe you guys can help. I understand that the atomic mass is the number of neutrons and protons collectively. I also understand that the atomic number represents the number of protons (also the number of electrons if the atom is electrically neutral). So here are the questions.

1.) Are atoms usually always electrically neutral?

b. If not- how do you tell how many electrons there are. I understand that there are usually 8 for an atom to be stable but obviously there are variables.

2.) How can you tell if an atom is electrically neutral? In the example below I see same amount ne/pro

3.)Also why is:

Carbon Atomic Number: 6 and Atomic Mass: 12 (and the books says it's electrically neutral) so 6 electrons as well~~ Why is that considered an isotope

Answer 1

1. For an atom to be atomically neutral, its number of electrons has to be equal to its number of protons. However, atoms, particularly those of elements on the ends of the atomic table,  have a tendency to prefer the 8 electrons in the valence shell. An atom has more electrons than that, but the eight surface ones are used in bonding. If an atom is not atomically neutral, its charge is written in the same location an exponent would be in standard math. If there is no charge written, you can assume an atom is neutral.

2. If the number of electrons (- particles) equals the number of protons (+ particles), the atom is neutral

3. Isotopes are the varying numbers of neutrons an element can have. A carbon with six neutrons is still a carbon, so it is an isotope, as would be a carbon with five or seven neutrons. Any atom with some number of protons or neutrons is technically an isotope