Question

Which orbital is the first to be filled in any atom? Why?

Short answer

The first orbital to be filled in any atom is the 1s orbital. This is because it has the lowest energy level and is closest to the nucleus. According to the Aufbau principle, electrons fill orbitals from lower energy levels to higher energy levels to ensure the most stable electron configuration.

Step-by-step solution

Understanding Atomic Structure

Every atom consists of protons, neutrons, and electrons. Protons and neutrons form the nucleus, while electrons occupy various energy levels around the nucleus called shells.

Organizing Electrons in Shells and Subshells

Electrons occupy shells (n=1,2,3...) and subshells (s, p, d, f). Each shell can have different types of subshells, and each type of subshell can accommodate a specific number of electrons. The s subshell can hold 2 electrons, p subshell 6, d subshell 10, and f subshell 14 electrons.

Notation for Subshells in Relation to Principal Quantum Number

The notation for subshells is given by combining the principal quantum number (n) with the type of the subshell (s, p, d, or f). For example, the s subshell in the first shell is represented as "1s".

Understanding the Aufbau Principle

The Aufbau principle states that electrons fill atomic orbitals according to increasing energy levels. The order in which electrons fill orbitals is given by the diagonal rule (based on the Madelung rule).

Identify the First Orbital to be Filled

Based on the Aufbau principle, the electrons in an atom fill the orbitals starting at the lowest energy level. The lowest energy level is the 1s subshell (n=1, s subshell). The 1s orbital will be filled first because it is closest to the nucleus and has the lowest energy level.

Explain Why the 1s Orbital is Filled First

The 1s orbital is filled first because it has the lowest energy level and is closest to the nucleus. According to the Aufbau principle, electrons fill orbitals from lower energy levels to higher energy levels to ensure the most stable electron configuration. So, the first orbital to be filled in any atom is the 1s orbital because it is the lowest energy level and the Aufbau principle states that this is how electrons fill orbitals in atoms to achieve the most stable configuration.