Bismuth (Bi), a heavy element with the atomic number 83, presents as a silvery-white metal often displaying a faint pink or iridescent hue. Its placement on the periodic table, near the elements traditionally called “heavy metals,” frequently leads to confusion regarding its precise classification.
Bismuth’s Official Classification
Bismuth is definitively not a transition metal. It is officially classified as a post-transition metal, sometimes referred to as a poor metal. This categorization places it in Group 15, also known as the nitrogen group, of the periodic table. As a post-transition element, Bismuth resides in the p-block. The term post-transition metal reflects its position just after the d-block elements, bridging the gap between true transition metals and the metalloids.
What Makes a Metal a Transition Metal
The classification of a metal hinges on its electronic structure, specifically the occupancy of its d-orbitals. By definition, a transition metal must have an atom or an ion with a partially filled d subshell. This incomplete orbital allows for the characteristic chemical behaviors of transition metals, such as forming compounds with multiple oxidation states and displaying color.
Bismuth’s electron configuration is \([Xe] 4f^{14} 5d^{10} 6s^2 6p^3\), which reveals why it falls outside this definition. The d-subshell, in this case the \(5d\) orbital, is completely filled with ten electrons. Since its neutral atom and its common ions, such as \(\text{Bi}^{3+}\), possess a filled \(d^{10}\) configuration, it cannot be a transition metal. Bismuth primarily utilizes its five valence electrons in the outermost \(6s\) and \(6p\) orbitals. The full \(d\) subshell means it lacks the unpaired \(d\) electrons that drive the magnetic and catalytic properties seen in true transition metals like iron or copper.
Unique Characteristics of Bismuth
Bismuth is notably non-toxic, especially when contrasted with its historical neighbor, lead, with which it was often confused. This low toxicity has made it a favored replacement for lead in applications requiring a heavy, dense metal.
Physical Properties
Bismuth is the most diamagnetic of all metals, meaning it is weakly repelled by a magnetic field. Its melting point is unusually low for a metal, at approximately \(271.5^\circ\text{C}\) (520.7°F). This low melting point is exploited in the creation of fusible alloys, such as those used in fire detection and suppression systems. Bismuth is also one of the few substances, alongside water, that expands as it solidifies. This expansion makes it useful for casting applications where a sharp, detailed impression is required, such as in type metal.
Industrial and Medical Uses
In medicine, a compound called Bismuth Subsalicylate is the active ingredient in common over-the-counter stomach remedies like Pepto-Bismol. Beyond pharmaceuticals, Bismuth compounds are used in cosmetics, where bismuth(III) chloride oxide provides a pearlescent, shimmering effect.