Antimony is a hard, brittle, bluish-white metalloid. It occurs mainly in the mineral stibnite (Sb2S3). Alloys of antimony are used to harden lead for batteries and bullets; compounds are used in flame retardants, semiconductors, and catalysts.
The ground-state electron configuration is [Kr] 4d10 5s2 5p3. With five valence electrons (\(5s^2 5p^3\)), antimony behaves like a pnictogen, commonly showing +3 and +5 oxidation states and forming covalent compounds.
Antimony most often exhibits +3 (stibous) and +5 (stibic) states.
Industrial extraction typically involves roasting followed by reduction:
\(\mathrm{Sb_2S_3 + 3\,O_2 \rightarrow Sb_2O_3 + 3\,SO_2}\)
\(\mathrm{Sb_2O_3 + 3\,C \rightarrow 2\,Sb + 3\,CO}\)
The roasted oxide \(\mathrm{Sb_2O_3}\) is reduced with carbon to yield metallic Sb.
Small percentages of Sb harden and strengthen soft lead by solid-solution and intermetallic strengthening, improving creep resistance and mechanical integrity. In lead–acid batteries this enhances grid strength; in ammunition it improves hardness and shape retention.
Antimony(III) oxide (Sb2O3) is a synergist with halogenated organics. On heating, it forms antimony halides that promote radical quenching in the gas phase, lowering flame propagation. It also contributes to char formation in some polymers.
Antimony is a metalloid. Compared with arsenic (more nonmetallic) and bismuth (more metallic), Sb sits in between: it forms covalent networks and semiconductors (e.g., InSb, GaSb) but also conducts better than typical nonmetals. Down group 15 (N → P → As → Sb → Bi), metallic character increases.
III–V antimonides are technologically important:
Sb2O3 is amphoteric, reacting with acids to form \(\mathrm{Sb^{3+}}\) salts and with strong bases to form antimonites:
\(\mathrm{Sb_2O_3 + 6\,H^+ \rightarrow 2\,Sb^{3+} + 3\,H_2O}\)
\(\mathrm{Sb_2O_3 + 2\,OH^- + H_2O \rightarrow 2\,[Sb(OH)_4]^-}\)
\(\mathrm{Sb^{3+}}\) can be reduced to metallic Sb, depositing a black/gray mirror on glass. One approach (under suitable reducing conditions) is represented schematically as:
\(\mathrm{Sb^{3+} + 3\,e^- \rightarrow Sb(s)}\)
This helps distinguish Sb from other cations in systematic analysis.
Soluble Sb(III) and Sb(V) compounds can be toxic if ingested or inhaled; chronic exposure may affect the lungs, skin, and cardiovascular system. In the lab/industry use fume hoods, gloves, and proper waste handling. Regulations limit Sb in drinking water and consumer products.