ANTIMONY

Name: Antimony (from ancient Greek: anti-monachos "monk-killer")

Symbol: Sb (from the original name, "Stibium", Stibius)

Group: 15

Period: 5

Block: p

Category: Metalloids

Atomic Number: 51

Atomic Mass: 121.760 u

Electrons per Shell: 2, 8, 18, 18, 5

Electronegativity: 2.05

Density: 6.697 g/cc

Melting Point: 630.63ºC

Boiling Point: 1635ºC

Thermal Conductivity: 24 W (m·K)

Electrical Conductivity: 2.5 × 10^6 S/m

Magnetic Order: Diamagnetic

Ordinary State: Solid

Oxidation States: 5, 4, 3, 2, 1, -1, -2, -3

Mohs Hardness: 3

Vickers Hardness: No data

Brinell Hardness: 294 MPa

Most stable isotopes: Sb-121 (57.21%) Sb-123 (42.79%)

Discoverer: Known since ancient times

Antimony (Sb), with atomic number 51, is a metalloid of group 15, with a density of 6.69 g/cm³ and an abundance of approximately 0.2 ppm in the Earth's crust, making it scarcer than arsenic (As, ~1.8 ppm). Known since Antiquity, antimony has been used in various cultures for its metallic appearance and versatility in alloys. Its name probably derives from the Greek anti-monachos ("against monks"), alluding to its toxicity, which caused the death of medieval alchemists, often confused with monks, during the golden age of alchemy (13th–17th centuries). This toxicity, similar to that of arsenic, with which it was historically confused, contributed to its lethal reputation. Another theory suggests that the term comes from the Arabic ithmid, used for the mineral stibnite (Sb₂S₃), which Egyptians employed as a cosmetic (kohl) for the eyes since ~3000 BC.

Although no specific discoverer is attributed, antimony was formally described in 1540 by the German mineralogist Georgius Agricola and later by the alchemist Basil Valentine, who documented its extraction from stibnite through reduction. In alchemy, antimony held special symbolism, represented by a wolf devouring the sun, and was considered a transformative material due to its ability to form alloys. Its identification as a chemical element solidified in the 18th century with the advancements of modern chemistry. In its pure state, antimony is brittle and lacks outstanding mechanical properties, but its value lies in its use as an alloying agent, improving the hardness and resistance of p-block metals, such as tin (Sn), lead (Pb), bismuth (Bi), and indium (In). In 2025, global antimony production (~140,000 tons annually) reflects its importance in specialized metallurgy, batteries, flame retardants, and electronics. Its toxicity (classified as a possible carcinogen by the IARC) requires careful handling, but its versatility in alloys, such as pewter (Sn-Sb) and solders (Pb-Sb), makes it indispensable in industrial applications, highlighting its role as the most "metallic" metalloid of group 15.

Antimony, with atomic number 51, is a metalloid of group 15, with a density of 6.69 g/cm³ and an abundance of approximately 0.2 ppm in the Earth's crust, making it scarcer than arsenic (As, 1.8 ppm). Its shiny gray appearance, with a pronounced metallic luster when freshly cast, resembles a true metal, making it the most "metallic" metalloid of group 15. However, its brittle nature and low abrasion resistance, with a hardness of ~3 on the Mohs scale, distinguish it from ductile metals like copper (Cu) or lead (Pb). Although fragile, with a compressive strength of ~3 GPa, antimony is easily pulverizable, which limits its use in its pure state. Its thermal conductivity (24 W/(m·K)) and electrical conductivity (2.5 × 10⁶ S/m) are low compared to metals like copper (5.9 × 10⁷ S/m), reinforcing its metalloid character.

Chemically, antimony is moderately resistant to corrosion. In ambient conditions, it remains stable in dry or humid air, forming a thin layer of antimony oxide (Sb₂O₃) that protects it from further oxidation. However, at high temperatures, it reacts with oxygen, sulfur (S), or halogens, forming compounds like antimony trisulfide (Sb₂S₃) or antimony chloride (SbCl₃). It resists mild acids, such as dilute hydrochloric acid (HCl), but is attacked by oxidizing acids like hot nitric acid (HNO₃) and hydrofluoric acid (HF). Its moderate reactivity and lower toxicity compared to arsenic (classified as a Group 1 carcinogen by the IARC) have allowed antimony to replace arsenic in many metallurgical applications, especially in alloys where safety is a priority.

The versatility of antimony lies in its capacity as an alloying agent, improving the hardness and resistance of p-block metals, such as tin (Sn), lead, bismuth (Bi), and indium (In). Although it lacks robust mechanical properties in its pure state, its incorporation into alloys, such as pewter (Sn-Sb) or solders (Pb-Sb), optimizes mechanical and chemical properties, making antimony a valuable material in specialized metallurgy. Its global production (~140,000 tons annually in 2025) reflects its importance in industrial applications, despite its moderate toxicity, which requires precautions in its handling.

Antimony, with atomic number 51, is a metalloid of group 15, with a density of 6.69 g/cm³ and an abundance of approximately 0.2 ppm in the Earth's crust. Unlike other metalloids like silicon or germanium, which focus on electronic or ceramic applications, antimony excels in metallurgy, where its capacity as an alloying agent significantly improves the mechanical and chemical properties of p-block metals. With a global production of about 140,000 tons annually in 2025 and an accessible cost (~8–12 USD/kg), antimony is a key component in alloys, semiconductors, and other industrial uses, leveraging its moderate corrosion resistance and lower toxicity compared to arsenic.

In metallurgy, antimony is widely used as a hardener in alloys of p-block metals, such as tin (Sn), lead (Pb), and bismuth (Bi). In pewter, a tin-based alloy, antimony acts as the second main alloying agent after copper (Cu), improving hardness, rigidity, and wear resistance, which extends the lifespan of decorative pieces, utensils, and jewelry. In lead alloys, such as those used in lead-acid batteries or bullets, antimony (typically 2–10%) increases rigidity and mechanical strength, reducing deformation under stress. It is also combined with bismuth in low-melting-point alloys, offering less toxic alternatives to lead, although bismuth and lead, neighbors in the periodic table, differ in reactivity and mechanical properties. These alloys, such as Babbitt alloy (Sn-Sb-Cu, with 7–15% Sb) and pot metal or white metal (generic terms for Sn, Pb, or Zn alloys with Sb), are used in bearings and cast parts due to their fluidity and low melting temperature (200–300 °C), facilitating the manufacture of components with complex shapes.

Outside of metallurgy, antimony plays a significant role as a dopant in semiconductors. By incorporating small quantities of antimony into metalloids like silicon (Si) or germanium (Ge), it donates an additional electron, improving electrical conductivity by creating negative charge carriers (n-type). This property is crucial in the manufacturing of diodes, transistors, and integrated circuits, although silicon dominates in these applications due to its greater abundance. Furthermore, antimony oxide (Sb₂O₃) is used as a flame retardant in plastics and textiles, leveraging its ability to inhibit combustion. Antimony's resistance to corrosion, thanks to the formation of a passivating layer of Sb₂O₃, and its lower toxicity compared to arsenic, have made it a preferred replacement in applications where safety is a priority, although its handling requires precautions due to its classification as a possible carcinogen by the IARC. The versatility of antimony, from alloys to semiconductors, underscores its importance in modern industry, despite its fragility in its pure state (~3 Mohs, ~3 GPa compressive strength).