The element defined by the presence of 67 protons in its nucleus is Holmium (Ho). This specific count establishes the element’s atomic number (Z=67), which dictates its fundamental chemical identity. When Holmium combines 67 protons with exactly 67 neutrons, the resulting atom is a synthetic form known as the isotope Holmium-134 (\(\text{Ho}^{134}\)). The mass number, calculated by summing the protons and neutrons, is 134, identifying this particular, highly unstable nuclear species.
The Defining Role of Protons
The organization of the periodic table rests upon the number of protons contained within an atom’s nucleus, known as the atomic number. This count is the single determinant of an element’s chemical nature. Every atom of Holmium must contain precisely 67 protons; any deviation results in an entirely different element.
In a neutral atom, the number of electrons equals the number of protons, which governs how the atom interacts with others to form molecules and compounds. The 67 electrons of Holmium arrange themselves in a configuration that places it within the lanthanide series.
This placement is due to the element’s unique electron configuration, specifically the filling of the \(4f\) electron shell, which is characteristic of the rare earth elements. The chemical behavior of Holmium, such as its tendency to form a trivalent ion (\(\text{Ho}^{3+}\)), is a direct consequence of the 67 protons balancing 67 electrons. The attraction between the 67 protons and the orbiting electrons defines the atomic radius, the ionization energy, and the specific chemical bonds that Holmium can form.
An atom with 66 protons is Dysprosium, and one with 68 protons is Erbium; the chemical properties of these elements are measurably distinct from Holmium. The count of 67 protons is a physical constant that locks the atom into its identity as Holmium.
Understanding the Resulting Isotope
The presence of 67 neutrons alongside 67 protons results in an atomic mass number of 134, creating the specific nuclide Holmium-134 (\(\text{Ho}^{134}\)). This combination classifies it as an isotope, an atom of an element that possesses an atypical number of neutrons. While the proton count defines the element, the neutron count dictates the specific isotope and strongly influences its nuclear stability.
The naturally occurring, stable isotope is Holmium-165, which contains 98 neutrons. The \(\text{Ho}^{134}\) isotope is extremely proton-rich and lies far outside the nuclear band of stability. This severe proton-neutron imbalance means that Holmium-134 is a synthetic radioisotope that can only be created in a laboratory, such as in a particle accelerator.
To achieve stability, this isotope must rapidly undergo radioactive decay to reach a more favorable proton-to-neutron ratio. Due to its proton excess, \(\text{Ho}^{134}\) is expected to decay almost instantaneously via either proton emission or beta-plus decay (positron emission), transforming into an isotope of Dysprosium (Z=66).
Based on the measured half-lives of other extremely light Holmium isotopes, the half-life of \(\text{Ho}^{134}\) is estimated to be incredibly short, likely in the microsecond or nanosecond range. This rapid decay means that Holmium-134 cannot be isolated or studied for any extended period of time. For heavier elements like Holmium, a significant surplus of neutrons is required to counteract the repulsive electrical forces between the numerous protons.
Properties and Applications of Holmium
Holmium is a soft, silvery-white metal and a member of the lanthanide series (rare earth elements). While the \(\text{Ho}^{134}\) isotope is unstable, the stable \(\text{Ho}^{165}\) isotope exhibits specialized physical properties. Holmium possesses the highest magnetic moment among all naturally occurring elements, a measure of its magnetic strength, making it an object of study in low-temperature physics.
This intense magnetic capability is exploited in creating the strongest artificially generated magnetic fields, where Holmium is used as a magnetic pole piece. Holmium is also a strong absorber of neutrons, a property useful in the nuclear industry. It is incorporated into control rods in nuclear reactors to regulate the fission chain reaction by capturing excess neutrons.
In the medical field, Holmium-doped materials are utilized in advanced laser technology, such as the Holmium-YAG laser. This solid-state laser emits infrared light highly absorbed by water and biological tissue. The precise energy delivery allows for minimally invasive surgical procedures, including breaking up kidney stones (lithotripsy) and removing soft tissue tumors.
Holmium oxide (\(\text{Ho}_{2}\text{O}_{3}\)) imparts a yellow or reddish-yellow color to specialized glass and cubic zirconia. These compounds are used as color standards for calibrating spectrophotometers, instruments that measure the intensity of light at different wavelengths. The combination of superior magnetic properties, neutron absorption, and specific optical characteristics solidifies Holmium’s role in high-technology and medical applications.