Refer to the figure above and then answer the question that follows.
-If an atom has an atomic number of 11, which of the electron shells are filled?

Question

Quizplus · Accepted Answer

The atomic number of an atom indicates the number of protons and, in a neutral atom, the number of electrons it has. An atom with an atomic number of 11 (sodium) has 11 electrons. The first shell can hold up to 2 electrons, and the second shell can hold up to 8 electrons. This fills the first shell (2 electrons) and the second shell (8 electrons), leaving 1 electron to start filling the third shell. Therefore, the first and second shells are filled.

Refer to the Figure Above and Then Answer the Question