The element with exactly 37 electrons in a neutral atom is Rubidium (Rb). An atom’s identity is defined by its atomic number (Z), which is the number of protons in its nucleus. Since the atom is electrically neutral, the number of electrons must match the number of protons. Therefore, Rubidium has 37 protons, placing its atomic number at Z=37.
The Element with 37 Electrons
Rubidium is positioned in Group 1 and Period 5 of the periodic table, classifying it as an alkali metal. It shares similar properties with elements like lithium, sodium, and potassium because they all possess a single electron in their outermost shell. Rubidium is a soft, silvery-white metal with a low melting point, characteristic of the alkali metal group. Its melting point is about \(39.3^\circ\)C (\(102.7^\circ\)F), low enough that it can liquefy on a warm day.
German chemists Robert Bunsen and Gustav Kirchhoff discovered Rubidium in 1861 by analyzing the mineral lepidolite using flame spectroscopy. They observed bright red spectral lines, which inspired them to name the element after the Latin word rubidus, meaning “deepest red”. Although Rubidium is relatively abundant in the Earth’s crust, it is found in low concentrations within other minerals, making its extraction complex.
How 37 Electrons Dictate Chemical Identity
The 37 electrons determine the element’s identity, while their specific arrangement governs its chemical behavior. Rubidium’s electrons are organized into distinct energy levels or shells. The electron shell configuration for Rubidium is \(2, 8, 18, 8, 1\), meaning the electrons are distributed across five main shells.
The single electron in the fifth and outermost shell is known as the valence electron. This electron is relatively far from the positively charged nucleus, resulting in a weak attractive force holding it in place. Because of this weak attraction, Rubidium has a low first ionization energy, meaning it requires little energy to remove this outermost electron.
This tendency to lose one electron dictates Rubidium’s high reactivity and its role in forming chemical compounds. By shedding this single valence electron, the atom achieves a stable electron configuration, resembling that of the noble gas Krypton. When this occurs, the atom transforms into a positively charged ion, Rb+, which readily forms ionic bonds with other elements. All alkali metals in Group 1 share this characteristic of easily forming a positive ion with a charge of +1.
Rubidium’s High Reactivity and Practical Uses
The presence of a single, easily lost valence electron results in Rubidium being a highly reactive metal. It reacts violently with water, producing rubidium hydroxide and hydrogen gas. This reaction is highly energetic, often releasing enough heat to ignite the hydrogen gas and cause an explosion.
Due to its high reactivity, elemental Rubidium must be stored in inert conditions, typically under mineral oil or in an atmosphere of an inert gas like argon. This prevents it from reacting spontaneously with oxygen or moisture in the air. Consequently, Rubidium is never found naturally in its pure metallic form.
A primary application of Rubidium is in atomic clocks, utilizing the slightly radioactive isotope Rubidium-87. The electrons in Rubidium-87 atoms have a specific energy transition frequency of approximately 6.8 billion cycles per second, providing a stable and accurate reference signal. These compact and affordable Rubidium standards are used extensively in global navigation satellite systems (GPS), telecommunications, and cell phone base stations.
Beyond timekeeping, Rubidium compounds find use in specialized glass manufacturing and in photocells, devices that generate electric current upon exposure to light. In medicine, the short-lived radioactive isotope Rubidium-82 is used in positron emission tomography (PET) scans for myocardial perfusion imaging. Because Rb+ ions behave similarly to potassium ions (K+) in the body, this isotope can help evaluate blood flow to the heart muscle.