The element with thirty-six protons in its nucleus is Krypton (Kr). The number 36 is uniquely tied to this specific element. Krypton is a rare, gaseous element discovered in 1898 by British chemists Sir William Ramsay and Morris W. Travers. Its name comes from the Greek word kryptos, meaning “the hidden one,” reflecting the difficulty in isolating it from liquid air.
The Significance of the Atomic Number
The identity of a chemical element is determined by the number of protons in its atomic nucleus, known as the atomic number. For Krypton, this number is 36. The nucleus also contains neutrons, which contribute to the atom’s mass, but their quantity can vary without changing the element’s identity.
Atoms of the same element with differing numbers of neutrons are called isotopes. For example, the most abundant naturally occurring isotope, Krypton-84, contains 48 neutrons and 36 protons, totaling a mass number of 84. In a neutral Krypton atom, the number of orbiting electrons equals the proton count (36), balancing the positive charge of the nucleus.
Krypton’s Distinctive Characteristics
Krypton is classified by its stable electronic structure, possessing a complete outer shell of eight valence electrons. This arrangement results in Krypton being a non-reactive, colorless, and odorless gas at standard temperature and pressure. It is largely unable to bond with other atoms under normal conditions.
Although generally considered inert, Krypton can be forced to react with highly electronegative elements like fluorine under extreme laboratory conditions. The compound Krypton difluoride (\(\text{KrF}_2\)) is the most commonly synthesized example. Krypton is also about three times heavier than air. Its boiling point is approximately \(-153.4^\circ\text{C}\), and its melting point is slightly lower at about \(-157.4^\circ\text{C}\).
Practical Applications and Natural Occurrence
Krypton is extremely rare in Earth’s atmosphere, making up only about one part per million by volume. Isolating Krypton for commercial use is a demanding process. This involves the fractional distillation of cooled and compressed liquid air, which separates atmospheric components based on their distinct boiling points.
The high cost of extraction is justified by the element’s specialized applications, primarily in lighting and advanced technology. Krypton’s heavier mass and low thermal conductivity improve efficiency when used as a filling gas in high-performance lighting.
Applications include:
- Incandescent and fluorescent lamps.
- High-speed photographic flashes and airport runway lights, due to its ability to emit a bright, whitish light when ionized.
- Excimer lasers used in applications like eye surgery.
- Energy-efficient, multi-pane window units, where its inert nature makes it an excellent insulator to reduce heat transfer.
Krypton plays a role in advanced technology. Historically, the isotope Krypton-86 was used to define the meter as a standard unit of length, based on the wavelength of its emitted light.