Question

Why do we believe that the valence electrons of calcium and potassium reside in the \(4 s\) orbital rather than in the \(3 d\) orbital?

Short answer

The valence electrons of calcium (Ca) and potassium (K) reside in the 4s orbital rather than the 3d orbital due to the energy levels and the Aufbau principle. The 4s orbital has a lower energy than the 3d orbital, making electrons fill the 4s orbitals first according to the Aufbau principle. As valence electrons are the outermost electrons available for chemical bonding, the electron configurations show that calcium and potassium have their valence electrons in the 4s orbitals.

Step-by-step solution

Recall the electron configurations of calcium and potassium

Before determining the valence electrons of calcium and potassium, let's recall their electron configurations. Calcium has an atomic number of 20, and potassium has an atomic number of 19. The electron configurations for these elements are: - Calcium (Ca): 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² - Potassium (K): 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹

Identify the valence electrons

We know that the valence electrons are the outermost electrons in an atom that are available for chemical bonding. In the electron configurations of calcium and potassium, we can see that their outermost electrons are located in the 4s orbital: - Calcium (Ca): 1s² 2s² 2p⁶ 3s² 3p⁶ \(\underline{4s^2}\) - Potassium (K): 1s² 2s² 2p⁶ 3s² 3p⁶ \(\underline{4s^1}\) The valence electrons for Ca and K reside in the 4s orbitals.

Understand energy levels and the Aufbau principle

Atomic orbitals have different energy levels, with 1s being the lowest and energy levels increasing from there. Electrons fill in the atomic orbitals following the Aufbau principle, which states that electrons will fill the lowest available energy level before filling higher energy levels. The 4s orbital has a lower energy than the 3d orbital, so the electrons will fill it first.

Explain why valence electrons are in the 4s orbital

Based on the energy levels, Aufbau principle, and electron configurations, we can conclude that the valence electrons of calcium and potassium reside in the 4s orbital rather than the 3d orbital. According to the Aufbau principle, electrons fill the lower energy level 4s orbitals before moving to the higher energy level 3d orbitals. Since the element's outermost electrons are responsible for chemical bonding and reactions, the valence electrons of both calcium and potassium are found in the 4s orbitals.