The identity of any chemical element is determined by the atomic number (Z), which is the number of protons in the nucleus. In a neutral atom, the number of negatively charged electrons must precisely match the number of positively charged protons. Therefore, an atom possessing exactly 50 electrons must also contain 50 protons, establishing its atomic identity. This fixed relationship allows for the precise identification of this element.
Identifying the Element with 50 Electrons
The element defined by an atomic number of 50 is Tin (Sn), derived from the Latin stannum. Tin is a post-transition metal situated in Group 14 and Period 5 of the periodic table, with a standard atomic weight of approximately 118.71 atomic mass units.
Its position in Group 14 places it in the same chemical family as carbon, silicon, and lead. The 50 electrons in a neutral Tin atom are arranged in the configuration 2, 8, 18, 18, and 4. The outermost valence shell contains four electrons, which dictates its chemical behavior. This structure allows Tin to exhibit two common oxidation states, losing either two or four electrons when forming compounds.
Key Physical and Chemical Characteristics of Tin
Tin is a silvery-white metal that is soft, pliable, and ductile at room temperature. It is malleable, meaning it can be easily hammered into thin sheets.
One of its characteristics is its low melting point of 231.9°C, the lowest among the elements in its group. Bending a bar of the metal produces a distinctive crackling noise called the “tin cry,” caused by the friction of slipping crystals.
Chemically, pure Tin is relatively unreactive and highly resistant to corrosion from water and air. It readily forms a thin, protective layer of stannic oxide on its surface. This layer prevents further oxidation of the underlying metal, allowing it to maintain its metallic appearance.
Common Uses and Practical Applications
The most recognizable application of Tin is its use in corrosion-resistant coatings, particularly for food storage containers. “Tin cans” are steel coated with a thin layer of Tin to prevent rusting and contamination. This use is possible because inorganic Tin compounds are considered non-toxic to humans.
Tin’s low melting point makes it a component in various alloys. Most notably, it is used in solder, which joins metals in plumbing and electronics. Historically, Tin was alloyed with copper to create bronze, dating back to 3000 BC.
Other Applications
Pewter is another common alloy, typically containing 85% to 99% Tin mixed with copper, antimony, or bismuth. Tin is also used in the float glass process, where molten glass is poured onto a bath of molten Tin to create a perfectly flat surface for window panes. Additionally, organic compounds containing Tin, known as organotin compounds, are employed as fungicides and antifouling agents for ships, though these compounds can be highly toxic.
The Different Structural Forms of Tin
Tin is an allotropic element, meaning it can exist in multiple distinct physical forms with different crystal structures under varying conditions. The two most common allotropes are beta-tin (β-Sn) and alpha-tin (α-Sn).
Beta-tin, or white tin, is the metallic, silvery, and malleable form that is stable at and above ordinary room temperature. It has a body-centered tetragonal crystal structure, which provides its metallic properties.
The structural shift occurs at a specific temperature of 13.2°C, below which alpha-tin, or gray tin, becomes the thermodynamically stable form. Alpha-tin has a diamond cubic crystal structure, making it a nonmetallic, brittle material.
This transformation from metallic white tin to nonmetallic gray tin is accompanied by a significant volume increase of approximately 27%. This expansion causes the metal object to crumble into a dull, gray powder, a phenomenon historically known as “tin pest” or “tin disease.” Although the transformation begins below 13.2°C, the process is notoriously slow to start, with the maximum rate of deterioration typically occurring at much colder temperatures, around -30°C to -40°C.