What is the ground-state electron configuration (noble-gas shorthand) for arsenic (As), atomic number 33?

• A. [Ar] 4s2 3d10 4p5
• B. [Ar] 4s2 3d10 4p3
• C. [Kr] 5s2 4d10 5p3
• D. [Ne] 3s2 3p6 4s2 3d10 4p3

Answer: (B)

Verified step by step guidance

1. Identify the atomic number of arsenic (As), which is 33. This tells us that arsenic has 33 electrons in its neutral ground state.
2. Recall that the noble-gas shorthand electron configuration uses the electron configuration of the previous noble gas as a starting point. Find the noble gas with an atomic number less than 33 but closest to it. In this case, it is argon (Ar) with atomic number 18.
3. Write the electron configuration of argon as the core: \([\text{Ar}]\). This accounts for the first 18 electrons.
4. Determine how many electrons remain to be placed after argon: \$33 - 18 = 15$ electrons. These electrons will fill the orbitals beyond argon in the order of increasing energy levels: 4s, 3d, and then 4p.
5. Fill the orbitals with the remaining 15 electrons following the Aufbau principle: 4s orbital gets 2 electrons, 3d orbital gets 10 electrons, and the remaining 3 electrons go into the 4p orbital. This gives the shorthand configuration: \([\text{Ar}] 4s^2 3d^{10} 4p^3\).