Question

which is the electron configuration for bromine?
○ ( 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^5 )
○ ( 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 )
○ ( 1s^2 2s^2 2p^6 3s^2 3p^4 4s^2 3d^{10} 4p^5 )
○ ( 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^9 4p^5 )

Explanation:

Step1: Recall bromine's atomic number

Bromine (Br) has an atomic number of 35, meaning it has 35 electrons. We need to build the electron configuration by filling orbitals following the Aufbau principle, Pauli exclusion principle, and Hund's rule.

Step2: Fill orbitals in order

The order of filling orbitals is \(1s\), \(2s\), \(2p\), \(3s\), \(3p\), \(4s\), \(3d\), \(4p\), etc.

• \(1s\) can hold 2 electrons: \(1s^2\) (2 electrons used)
• \(2s\) can hold 2 electrons: \(2s^2\) (total 4)
• \(2p\) can hold 6 electrons: \(2p^6\) (total 10)
• \(3s\) can hold 2 electrons: \(3s^2\) (total 12)
• \(3p\) can hold 6 electrons: \(3p^6\) (total 18)
• \(4s\) can hold 2 electrons: \(4s^2\) (total 20)
• \(3d\) can hold 10 electrons: \(3d^{10}\) (total 30)
• Now we have 35 - 30 = 5 electrons left for the \(4p\) orbital: \(4p^5\)

Putting it all together: \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^5\)

Let's check the other options:

• Second option: \(4p^6\) would mean 36 electrons (bromine has 35), so incorrect.
• Third option: The order of \(3p\) and \(4s\) is wrong (should fill \(4s\) before \(3d\), but also the \(3p\) and \(4s\) order here is messed up; correct order after \(3p\) is \(4s\), not \(4s\) after \(3p\) in a wrong sequence. Wait, no, the third option has \(3s^2 3p^4\) which is incorrect (3p should have 6 electrons for atomic number up to here), so wrong.
• Fourth option: \(3d^9\) is incorrect, \(3d\) should have 10 electrons after filling \(4s^2\) (since \(d\) orbitals can hold 10, and we fill \(4s\) before \(3d\), then \(3d\) gets 10 electrons for elements after calcium).

Answer:

\(1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^5\) (the first option)