Question

which is the electron configuration for an oxygen atom?
$1s^2 2s^2 2p^4$
$1s^2 2s^2 2p^6 3s^2 3p^6$
$1s^2 2s^2 2p^6$
$1s^2 2s^2 2p^6 3s^2 3p^6 4s^2$

Explanation:

Step1: Recall oxygen's atomic number

Oxygen has an atomic number of 8, so it has 8 electrons.

Step2: Apply electron configuration rules

Electrons fill orbitals in order: 1s, 2s, 2p, 3s, etc. The 1s orbital holds 2, 2s holds 2, then 2p. For 8 electrons: \(1s^2 2s^2 2p^4\) (2 + 2 + 4 = 8).

Step3: Analyze options

• First option: \(1s^2 2s^2 2p^4\) (sum 8, correct for O).
• Second: \(1s^2 2s^2 2p^6 3s^2 3p^6\) (sum 18, Ar or K⁺/Ca²⁺).
• Third: \(1s^2 2s^2 2p^6\) (sum 10, Ne or Na⁺/Mg²⁺).
• Fourth: \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^2\) (sum 20, Ca).

Answer:

The first option: \(1s^2 2s^2 2p^4\)