Polonium (Po) is a rare and highly radioactive element discovered by Marie Curie in 1898. Found naturally in trace amounts within uranium ores, it is difficult to study due to its scarcity and intense alpha-particle emission. Understanding polonium requires determining the precise number and arrangement of its electrons.
Determining the Total Electron Count
The total number of electrons in a neutral atom must exactly match the number of protons contained within the nucleus. This proton count is known as the atomic number (\(Z\)). Polonium has an atomic number of 84 (Po, \(Z=84\)).
Since the atomic number is 84, a neutral polonium atom contains 84 protons. To balance this positive charge, the atom must also contain exactly 84 electrons. Any deviation from this count results in an ion, an atom with a net electrical charge.
Electron Shells and Configuration
The 84 electrons are arranged in specific energy levels, or shells, surrounding the nucleus. These shells are filled sequentially from the lowest energy level outward, following quantum mechanical rules. Polonium is a large atom, requiring six distinct principal quantum shells to house all its electrons.
The detailed distribution is represented by the electronic configuration: \([\text{Xe}] 4f^{14} 5d^{10} 6s^2 6p^4\). The \([\text{Xe}]\) configuration accounts for the first 54 electrons (Xenon). The remaining 30 electrons fill the \(4f\) and \(5d\) sublevels completely before reaching the outermost shell.
The outermost shell is the sixth energy level, containing the remaining six electrons distributed as \(6s^2 6p^4\). These six electrons are the valence electrons, determining how the atom interacts with other elements to form chemical bonds. The full shell structure can be summarized as 2, 8, 18, 32, 18, 6.
How Polonium’s Electron Structure Impacts Its Behavior
The presence of six valence electrons (\(6s^2 6p^4\)) immediately places polonium into Group 16 of the periodic table, alongside oxygen, sulfur, and tellurium. This positioning suggests it should behave as a non-metal or metalloid, often seeking to gain two electrons to achieve a stable octet configuration. However, the element’s large size, resulting from its six electron shells, significantly modifies its properties.
As electrons are added to successively larger shells, the outer valence electrons become increasingly shielded from the positive charge of the nucleus by the inner electron layers. This effect, combined with its high atomic mass, causes polonium to exhibit a distinctly metallic character. It behaves more like a metal than the lighter elements in Group 16 and is commonly classified as a post-transition metal or a metalloid.
The sheer number of subatomic particles (84 protons and a corresponding high number of neutrons) makes the polonium nucleus inherently unstable. This large size is why polonium has no stable isotopes and is highly radioactive, undergoing alpha decay. The large electron cloud contributes to the atom’s overall size, lessening the nuclear attraction on the outer electrons and influencing its relatively low first ionization energy compared to its group members.