The Noble Gas Goal
Why atoms want stable electron shells
What this lesson covers
Why it matters
Sodium is a violent metal; chlorine is a toxic gas. Together, they form the calm, stable salt on your dinner table.
Predict first
Why does sodium give up an electron to chlorine?
Atoms react to fill their outer shells, mimicking the stable octet or duplet of noble gases.
- To achieve a stable noble gas electron configuration — correct
- Because chlorine is physically larger than sodium
- To become positively charged for no reason
- Because electrons are heavy and fall into chlorine
What you do
Build a sodium atom — 11 protons, 12 neutrons and 11 electrons (mass number 23). Remove one electron. Now build chlorine (17 protons) and add one electron. Observe the new shell structures.
Check yourself
What is the electron configuration of the sodium ion (Na⁺)?
Na (2,8,1) loses 1 electron to become Na⁺ (2,8), matching the noble gas Neon.
Why does chlorine gain an electron?
Cl (2,8,7) gains 1 electron to become Cl⁻ (2,8,8), matching the noble gas Argon.
Which noble gas configuration does a helium atom represent?
Helium has only the first shell, which is full with 2 electrons (duplet).
- 2, 8, 1
- 2, 8 — correct
- 2, 8, 8
- 2, 7
- To complete its octet and match Argon's configuration — correct
- To become neutral
- Because it is greedy
- To match Sodium's configuration
- Octet (8 electrons)
- Duplet (2 electrons) — correct
- Zero electrons
- 4 electrons