Question

which electron configuration shows the arrangement of electrons in an atom of bromine?
○ k $4s^2 3d^{10} 4p^5$
○ ar $4s^2 3d^{10} 4p^5$
○ $1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 4d^{10} 4p^5$
○ $1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 2p^6 3p^6 4p^5 4d^{10}$

Explanation:

Step 1: Recall the atomic number of bromine

Bromine (Br) has an atomic number of 35, meaning it has 35 electrons.

Step 2: Analyze the electron configuration options

• First option: \([K]4s^2 3d^{10} 4p^5\) – Potassium (K) has 19 electrons. \(19 + 2 + 10 + 5 = 36\) electrons (too many, since Br has 35).
• Second option: \([Ar]4s^2 3d^{10} 4p^5\) – Argon (Ar) has 18 electrons. \(18 + 2 + 10 + 5 = 35\) electrons (matches Br's electron count).
• Third option: \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 4d^{10} 4p^5\) – Let's count: \(2 + 2 + 6 + 2 + 6 + 2 + 10 + 5 = 35\)? Wait, no, the order of filling is wrong. 4d orbitals fill after 5s, but here 4d is filled before 4p? No, the correct order is \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^5\) (which is the same as \([Ar]4s^2 3d^{10} 4p^5\) since Ar is \(1s^2 2s^2 2p^6 3s^2 3p^6\)). The third option has \(4d^{10}\) before \(4p^5\), which is incorrect orbital filling order (4p fills before 4d).
• Fourth option: \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 2p^6 3p^6 4p^5 4d^{10}\) – This has duplicate and incorrect orbitals (2p and 3p repeated, wrong filling order), and the electron count is way off.

Step 3: Confirm the correct configuration

The correct electron configuration for Br (35 electrons) is \([Ar]4s^2 3d^{10} 4p^5\) because Ar (18 e⁻) + \(4s^2\) (2) + \(3d^{10}\) (10) + \(4p^5\) (5) = \(18 + 2 + 10 + 5 = 35\) electrons, and the orbital filling order is correct (4s, then 3d, then 4p).

Answer:

\([Ar]4s^2 3d^{10} 4p^5\) (the second option in the provided choices)