Give the ground state electron configuration for Se

Give the ground state electron configuration for Se. [Ar]4s²3d¹⁰4p⁴ [Ar]4s²4d¹⁰4p⁴ [Ar]4s²3d¹⁰4p⁶ [Ar]4s²3d¹⁰ [Ar]3d¹⁰4p^4</sup

The Correct Answer and Explanation is:

Correct Answer: [Ar]4s²3d¹⁰4p⁴

Explanation

The electron configuration of an element describes the arrangement of its electrons in atomic orbitals in its ground state, which is the most stable, lowest-energy state. To determine the ground state electron configuration for Selenium (Se), we follow the Aufbau principle, which dictates that electrons fill orbitals starting from the lowest energy level and moving upwards.

1. Identify the Atomic Number: First, locate Selenium (Se) on the periodic table. It is in Group 16 and Period 4, with an atomic number (Z) of 34. This means a neutral selenium atom contains 34 protons and 34 electrons.
2. Use Noble Gas Notation: For convenience, we can use noble gas notation to abbreviate the configuration. We find the noble gas that precedes selenium in the periodic table, which is Argon (Ar). Argon has an atomic number of 18, so its electron configuration (1s²2s²2p⁶3s²3p⁶) can be represented as [Ar]. This accounts for the first 18 electrons of selenium.
3. Fill the Remaining Orbitals: We need to place the remaining 34 – 18 = 16 electrons into the orbitals of the next energy level, which corresponds to the fourth period (n=4).
   • Following the order of orbital filling, the two electrons after the argon core enter the 4s orbital. This gives us [Ar]4s². We have now placed 18 + 2 = 20 electrons.
   • Next, we fill the 3d orbitals. Although the principal quantum number is 3, the 3d subshell is higher in energy than the 4s subshell but lower than the 4p. The 3d subshell can hold a maximum of 10 electrons. Filling this completely gives us [Ar]4s²3d¹⁰. This accounts for 20 + 10 = 30 electrons.
   • Finally, we must place the remaining 34 – 30 = 4 electrons. These electrons go into the next available subshell, which is the 4p subshell. This results in the configuration [Ar]4s²3d¹⁰4p⁴.

The final electron count is 18 (from [Ar]) + 2 (in 4s) + 10 (in 3d) + 4 (in 4p) = 34, which correctly matches the atomic number of Selenium.