Holmium is a rare earth metal with the chemical symbol Ho, and it belongs to the lanthanide series on the periodic table. It is a soft, silvery metal, and like other elements in its group, it is highly reactive, slowly forming a yellowish oxide coating when exposed to air. The element was discovered in 1878 and was named after “Holmia,” the Latinized name for Stockholm, Sweden.
Defining Atomic Structure Variables
Understanding the number of neutrons in any element requires familiarity with the fundamental components that define an atom’s structure. The Atomic Number (\(Z\)) specifies the number of protons contained within an atom’s nucleus. This number is unique to each element and determines its identity; for instance, any atom with 67 protons is, by definition, Holmium.
The second concept is the Mass Number (\(A\)), which represents the total count of particles found in the nucleus: the protons and the neutrons. Since electrons have negligible mass, the mass number essentially gives the total weight of the atom’s core. This number is always a whole number and is used to label specific versions of an element.
The relationship between these two numbers provides the key to finding the neutron count. To determine the number of neutrons, subtract the atomic number (protons) from the mass number (protons plus neutrons). The equation for finding the neutron count is \(Neutrons = Mass Number (A) – Atomic Number (Z)\).
Determining Holmium’s Neutron Count
Applying these principles directly to Holmium allows for the calculation of its neutron count. Holmium’s atomic number (\(Z\)) is 67, which means every Holmium atom contains exactly 67 protons in its nucleus. This fixed number of protons is what gives Holmium its chemical properties.
Natural Holmium is considered a monoisotopic element, meaning it exists naturally as only one stable form, which is Holmium-165 (\(\text{}^{165}\text{Ho}\)). The number 165 is the mass number (\(A\)) of this stable isotope, representing the total count of protons and neutrons in its nucleus.
To find the number of neutrons in this stable form, the calculation is performed using the formula \(Neutrons = A – Z\). Subtracting the atomic number (67 protons) from the mass number (165 total particles) yields the neutron count. The result is \(165 – 67 = 98\), meaning the most common and naturally occurring form of Holmium has 98 neutrons.
The Concept of Holmium Isotopes
While 98 neutrons is the count for the stable, naturally occurring form, the neutron count can vary depending on the specific atom. Atoms of the same element with the same number of protons but a different number of neutrons are called isotopes. Holmium is unique because 100% of the Holmium found in nature is the \(\text{}^{165}\text{Ho}\) isotope.
However, scientists have synthesized many other non-naturally occurring isotopes of Holmium in laboratories. The known isotopes of Holmium range widely, from Holmium-140 (\(\text{}^{140}\text{Ho}\)) to Holmium-175 (\(\text{}^{175}\text{Ho}\)). Each of these different versions has a unique neutron count, although they all retain 67 protons.
For instance, the lightest known isotope, Holmium-140, has 73 neutrons (\(140 – 67 = 73\)), while the heaviest, Holmium-175, contains 108 neutrons (\(175 – 67 = 108\)). These synthetic isotopes are unstable and undergo radioactive decay. Holmium-163 (\(\text{}^{163}\text{Ho}\)), the most stable radioactive form, has a half-life of 4,570 years. While 98 neutrons is the standard answer for natural Holmium, other isotopes can vary significantly.
Applications of Holmium in Science and Industry
Holmium’s unique properties, particularly its strong interaction with magnetic fields and light, have led to several specialized applications. Holmium possesses the highest magnetic permeability and magnetic saturation of any element, making it useful in creating pole pieces for the strongest static magnets. These materials are utilized in research and in devices requiring intense magnetic fields.
Holmium-doped materials are used to create specialized solid-state lasers that emit light at a wavelength of 2.1 micrometres. These lasers are valued in medicine for procedures like breaking up kidney stones and for various dental and surgical applications because the laser light is readily absorbed by water in soft tissues.
Holmium oxide is employed as a coloring agent to impart a yellow or reddish tint to cubic zirconia and certain types of glass. Because it readily absorbs neutrons, the element is sometimes used in nuclear reactors as a “burnable poison” to help regulate the chain reaction.