Tin is a soft, silvery post-transition metal used mainly in solders and protective tinplate. It has two allotropes: metallic β-tin (stable above 13.2 °C) and brittle α-tin (stable below 13.2 °C), a transition known as “tin pest.”
The ground-state configuration is [Kr] 4d10 5s2 5p2. With four valence electrons (5s25p2), tin can exhibit both +2 and +4 oxidation states depending on conditions and ligand environment.
Tin most commonly shows +2 (stannous) and +4 (stannic) states:
Tin pest is the allotropic transformation of metallic, ductile β-Sn (tetragonal) into brittle, gray α-Sn (diamond-cubic) below 13.2 °C. The lower-temperature phase has a more open structure and larger specific volume, causing disintegration of parts over time in cold conditions.
The tin cry is a crackling sound produced when bars or foils of β-Sn are bent. It arises from deformation twinning and the breaking/reforming of metallic bonds along crystal planes—audible because tin is soft and deforms readily.
With non-oxidizing acids, Sn(0) is oxidized to Sn(II) while hydrogen is evolved:
\(\mathrm{Sn(s) + 2\,HCl(aq) \rightarrow SnCl_2(aq) + H_2(g)}\)
Tin(IV) oxide is amphoteric: it reacts with strong bases to form hexahydroxostannate:
\(\mathrm{SnO_2(s) + 2\,OH^- + 2\,H_2O \rightarrow [Sn(OH)_6]^{2-}}\)
Tinplate is steel coated with a thin layer of Sn. Tin provides a dense, adherent barrier against corrosion and is relatively non-toxic, making it suitable for food packaging. Modern cans often use lacquers to further protect both tin and steel from acidic contents.
Tin whiskers are hair-like metallic filaments that can spontaneously grow from electroplated Sn finishes, potentially causing electrical shorts. Mitigation strategies include adding small amounts of Pb (where permitted), using Ni barrier layers, annealing, or applying conformal coatings.
\(\mathrm{SnCl_2}\) (stannous) is a reducing agent used in analytical chemistry and electroplating; it dissolves in water to give hydrolyzed Sn(II) species. \(\mathrm{SnCl_4}\) (stannic) is a volatile, covalent liquid that fumes in moist air and hydrolyzes to oxo-chlorides; it’s used as a catalyst/reagent in organic synthesis and for making \(\mathrm{SnO_2}\) coatings.
Metallic tin and many inorganic tin salts have moderate toxicity profiles. However, organotin compounds (e.g., tributyltin) can be highly toxic to aquatic life and have been heavily restricted worldwide. Handle tin chemicals with gloves/eye protection and follow disposal regulations.