Understanding Holmium (Ho)
Holmium (Ho) is a chemical element with atomic number 67. It belongs to the lanthanide series, a group of rare-earth elements known for their distinctive electronic structures and magnetic properties. These elements are found in various minerals worldwide, with significant mining operations in regions such as China, Australia, and the United States.
Atomic Number and Mass Number
The atomic number (Z) of an element defines the number of protons in the nucleus of an atom and uniquely identifies the element. For Holmium, the atomic number is 67. The most common isotope of Holmium has a mass number (A) of 165. The mass number represents the total count of protons and neutrons in the nucleus.
Protons, Neutrons, and Electrons
- Protons: The number of protons in a neutral Holmium atom is equal to its atomic number. Therefore, a Holmium atom contains 67 protons.
- Electrons: In a neutral atom, the number of electrons orbiting the nucleus is equal to the number of protons to balance the positive charge. Thus, a neutral Holmium atom contains 67 electrons.
- Neutrons: The number of neutrons can be determined by subtracting the atomic number from the mass number. For the most common isotope of Holmium ($^{165}$Ho), the number of neutrons is 165 (mass number) - 67 (atomic number) = 98 neutrons.
Electron Configuration
The electron configuration describes the arrangement of electrons in an atom’s orbitals. For Holmium, with 67 electrons, its electron configuration follows the Aufbau principle, Hund’s rule, and the Pauli exclusion principle.
The electron configuration of a neutral Holmium atom is: $$1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^2 4d^{10} 5p^6 6s^2 4f^{11}$$
This configuration can be condensed using the noble gas notation, referencing the electron configuration of Xenon (Xe), which is the noble gas preceding Holmium. Xenon has 54 electrons. The condensed electron configuration for Holmium is: $$[Xe] 4f^{11} 6s^2$$
This notation indicates that the first 54 electrons are arranged like those in a Xenon atom, followed by 11 electrons in the 4f subshell and 2 electrons in the 6s subshell. The 4f subshell is being filled for elements in the lanthanide series.
Explaining Valence Electrons
Valence electrons are the electrons located in the outermost electron shell of an atom. These electrons are primarily involved in chemical bonding and determine an element’s chemical properties.
For Holmium, the highest principal energy level (n) is 6, which contains the $6s^2$ electrons. These two electrons are considered the primary valence electrons and are typically the first to be involved in chemical reactions. While the 4f subshell is an inner shell, the electrons within it can also participate in bonding due to their relatively close energy levels to the outermost electrons and the unique characteristics of rare-earth elements. However, for many high school level discussions, the outermost $6s^2$ electrons are the most straightforward representation of valence electrons.