The outermost shell stops at eight

The idea

The outermost shell of an atom can hold at most 8 electrons; the first shell can hold at most 2.

A limit at the edge

The M shell can hold up to 18 electrons by the 2n² rule. But there is another rule for the outermost shell.

When the M shell is the outermost shell of an atom, what is the most it can hold?

• 8
• 18
• 2

Three outermost shells

Press Next step to look at three atoms.

Eight and two

The 2n² rule gives the most a shell can hold. For the outermost shell there is a smaller limit: 8 electrons. If the first shell is the outermost, it holds at most 2.

The outermost shell of an atom can hold at most 8 electrons. The first shell can hold at most 2.

Notes

The outermost shell holds at most 8 electrons; the first shell holds at most 2.

Check yourself

What is the most electrons the outermost shell of an atom can hold?

What is the most the first shell can hold?

Which statement is correct?

• 18. The M shell can hold up to 18 by the 2n² rule, but the outermost shell can hold at most 8.
• 8 — correct. Yes!
• 2. Two is the most for the first shell.
• 8. Eight is the most for an outermost shell, but the first shell holds at most 2.
• 1. The first shell can hold 2 electrons, as 2 × 1² = 2.
• 2 — correct. Yes!
• The outermost shell holds at most 8 electrons, and the first shell at most 2 — correct. Yes!
• Every outermost shell holds exactly 8 electrons. The rule says at most 8. Hydrogen has just one electron, in its first shell.
• An outermost M shell can hold up to 18 electrons. The outermost shell holds at most 8, even when it is the M shell.