Tin is a distinctive element characterized by its soft, pliable, silvery-white metallic appearance and remarkable resistance to corrosion, primarily due to a protective oxide film. It is well-known for its relatively low melting point and its unique allotropic forms.
General Characteristics of Tin
Tin (Sn), a post-transition metal in Group 14 of the periodic table, exhibits several key physical attributes:
- Appearance: It is a lustrous, silvery-white metal that polishes to a high shine.
- Softness & Pliability: Tin is notably soft and highly pliable, meaning it can be easily bent, hammered, or pressed into thin sheets without breaking. It is also ductile, allowing it to be drawn into wire.
- Corrosion Resistance: One of tin's most valuable physical properties is its excellent resistance to corrosion. This is because it readily forms a thin, stable, and protective oxide film on its surface when exposed to air, which prevents further oxidation.
- Density: Tin is a moderately dense metal.
- Low Melting Point: It has a comparatively low melting point for a metal.
Key Physical Data for Tin
The following table summarizes some fundamental physical properties of tin:
| Property | Value |
|---|---|
| Atomic Number | 50 |
| Symbol | Sn |
| Appearance | Silvery-white, lustrous metal |
| Melting Point | 231.93 °C (449.47 °F) |
| Boiling Point | 2602 °C (4716 °F) |
| Density (White Tin) | 7.28 g/cm³ |
| Mohs Hardness | 1.5 |
| Crystal Structure | Tetragonal (White Tin), Cubic Diamond (Gray Tin) |
| Electrical Conductivity | 9.17 × 10⁶ S/m (at 20°C) |
| Thermal Conductivity | 66.8 W/(m·K) (at 27°C) |
| Malleability | Very high |
| Ductility | High |
For more detailed data, refer to reputable sources like PubChem.
Mechanical Properties
Malleability and Ductility
Tin is highly malleable, meaning it can be hammered or rolled into very thin sheets without cracking. This property is utilized in applications such as tin foil (though modern "tin foil" is usually aluminum) and tin plating. It is also reasonably ductile, allowing it to be drawn into wires.
Softness and Pliability
As a soft metal with a Mohs hardness of approximately 1.5, tin can be easily scratched, bent, and shaped. This pliability makes it easy to work with and contributes to its use in alloys and coatings.
Thermal and Electrical Properties
Thermal Conductivity
Tin is a good conductor of heat, which is typical for metals. Its thermal conductivity allows it to effectively transfer heat, a property important in solders and certain alloys.
Electrical Conductivity
Like most metals, tin is an excellent electrical conductor, though not as good as copper or silver. Its conductivity is sufficient for its use in electronic components and solders, where it provides reliable electrical connections.
Melting and Boiling Points
Tin has a relatively low melting point (231.93 °C), making it easy to melt and cast, or to use as a solder. Its high boiling point (2602 °C) indicates its stability at high temperatures once solidified.
Chemical Resistance
Tin's resistance to corrosion is a standout physical property. It is not easily oxidized in air because its surface forms a durable, passive oxide layer. This protective film allows tin to resist corrosion from distilled, sea, and soft tap water. However, this resistance is not universal; tin can be attacked by strong acids, alkalis, and acid salts, which can dissolve its protective layer and lead to degradation.
Allotropy: The Case of Tin Pest
One of tin's most intriguing physical properties is its allotropy, meaning it can exist in more than one crystal structure (and thus physical form) under different conditions. The two most common allotropes are:
White Tin (β-Sn)
- Structure: Tetragonal crystal structure.
- Appearance: The familiar silvery-white metallic form.
- Stability: Stable at room temperature and above 13.2 °C (55.8 °F).
Gray Tin (α-Sn)
- Structure: Cubic diamond crystal structure (similar to silicon and germanium).
- Appearance: A brittle, non-metallic, grayish powder.
- Stability: Stable below 13.2 °C (55.8 °F).
Below 13.2 °C, white tin slowly transforms into gray tin. This transformation, known as "tin pest" or "tin disease," causes metallic tin objects to crumble into a powder. This phenomenon was historically problematic in cold climates, affecting tin buttons, organ pipes, and other tin artifacts, highlighting a crucial aspect of tin's physical behavior at low temperatures. Understanding this allotropic transition is vital for applications where tin is exposed to cold environments.
