Introduction to Polonium
Polonium (Po) is a rare and highly radioactive metalloid element. It was discovered by Marie and Pierre Curie in 1898 and named after Marie Curie’s native country, Poland. As a member of Group 16 (the Chalcogens) in the periodic table, it exhibits properties intermediate between metals and non-metals, though its metallic character is more pronounced than that of lighter chalcogens like sulfur or selenium.
Basic Atomic Properties
The atomic structure of polonium is defined by its atomic number and mass number.
Subatomic Particles
- Atomic Number (Z): Polonium has an atomic number of 84. This number uniquely identifies the element and represents the number of protons in the nucleus of every polonium atom.
- Protons: 84
- Electrons: In a neutral atom of polonium, the number of electrons is equal to the number of protons.
- Electrons: 84
- Mass Number (A): While polonium has numerous isotopes, Polonium-210 (²¹⁰Po) is one of the most studied and relevant isotopes, having a mass number of 210. The mass number is the total count of protons and neutrons in the nucleus.
- Neutrons: To find the number of neutrons in Polonium-210, subtract the atomic number from the mass number: A - Z = 210 - 84 = 126 neutrons.
- For other isotopes, such as Polonium-209 (²⁰⁹Po), the number of neutrons would be 209 - 84 = 125.
Electron Configuration
The arrangement of electrons in the different energy shells and subshells around the nucleus is known as the electron configuration. For polonium (atomic number 84), the full electron configuration is:
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁴
This can also be written in a condensed form using the noble gas core of Xenon (Xe), which has 54 electrons:
[Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁴
This configuration indicates that after the filled shells up to xenon, there are 14 electrons in the 4f subshell, 10 electrons in the 5d subshell, and then 2 electrons in the 6s subshell and 4 electrons in the 6p subshell.
Valence Electrons
Valence electrons are the electrons located in the outermost principal energy level (shell) of an atom. These electrons are primarily involved in chemical bonding. For polonium, the outermost principal energy level is n=6.
From the electron configuration [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁴, the electrons in the sixth energy level are:
- 6s²
- 6p⁴
Therefore, the total number of valence electrons for polonium is 2 + 4 = 6. This aligns with its position in Group 16 of the periodic table, as elements in this group typically possess six valence electrons.