How many valence electrons does an atom with five total electrons have?

An atom of the element calcium has 20 protons and 20 neutrons. Determine the following information about calcium:

(a) Number of electrons

(b) Atomic number

(c) Atomic weight

(d) Number of electrons in each energy level

A proton ___________:

The average oxygen atom has a mass number of 16 and an atomic number of 8. This means that the number of neutrons in this oxygen atom is:

Which of the following is true about electron energy shells?

A neon atom (Ne) is unreactive for which of the following reasons?

How many electrons does an Oxygen atom need to fulfill the octet rule by filling its valence shell?