Bismuth (Bi) is a heavy, silvery-white post-transition metal that occupies position 83 on the periodic table. Although its most common isotope, Bismuth-209, is technically radioactive, its half-life is extraordinarily long. Estimated at \(2.01 \times 10^{19}\) years, this half-life is billions of times longer than the age of the universe. Therefore, Bismuth can be treated as completely stable for all practical applications.
Total Electrons and Atomic Identity
The number of electrons in a neutral Bismuth atom is determined by its atomic number (\(Z\)). The atomic number represents the exact number of protons found in the nucleus. Since Bismuth has an atomic number of 83, it contains 83 protons.
For an atom to be electrically balanced in its neutral, ground state, the number of negatively charged electrons must precisely equal the number of positively charged protons. Therefore, a neutral Bismuth atom contains exactly 83 electrons. This consistent relationship holds true for every element.
The 83 electrons are organized into specific energy levels and subshells, which dictates the atom’s size and reactivity. This balance is only disrupted when Bismuth atoms gain or lose electrons, becoming charged ions.
Mapping the Electron Configuration
The 83 electrons in Bismuth are arranged in a complex, multi-layered structure of electron shells and subshells around the nucleus. This configuration maps where each electron is likely to be found and is described by principal quantum numbers representing the main energy levels. Bismuth distributes its electrons across six main shells, designated 1 through 6.
Within these main shells are specific subshells, designated \(s\), \(p\), \(d\), and \(f\). The complete, ground state electron configuration for Bismuth is \(1s^2 2s^2 2p^6 3s^2 3p^6 3d^{10} 4s^2 4p^6 4d^{10} 4f^{14} 5s^2 5p^6 5d^{10} 6s^2 6p^3\).
A more concise way to represent this is using the noble gas core notation, which accounts for the first 54 electrons by referencing Xenon (\([Xe]\)). The remaining 29 electrons are listed as \([Xe] 4f^{14} 5d^{10} 6s^2 6p^3\). This shorthand emphasizes that the vast majority of electrons are deep within the atom and are chemically inert. The electrons in the outermost shell control Bismuth’s interactions with other elements.
The Role of Valence Electrons
The chemical behavior and bonding of Bismuth are governed entirely by its outermost electrons, known as the valence electrons. These electrons reside in the \(n=6\) main energy level, specifically the \(6s^2\) and \(6p^3\) subshells, giving Bismuth a total of five valence electrons.
Bismuth belongs to Group 15 of the periodic table, often called the Pnictogens, and all elements in this group share this characteristic five-electron valence shell. Bismuth can potentially lose or share all five of these electrons, leading to an oxidation state of \(+5\). However, the \(+5\) state is relatively rare for Bismuth compared to its lighter neighbors.
Bismuth most commonly exhibits an oxidation state of \(+3\) in its compounds. This preference is due to the “inert pair effect,” which is pronounced in heavy elements like Bismuth. The two electrons in the \(6s\) subshell are held so tightly to the nucleus that they are reluctant to participate in chemical bonding. Consequently, Bismuth often only utilizes the three \(6p\) electrons for bonding, resulting in the more stable and frequently observed \(+3\) oxidation state.