Introduction to Cadmium (Cd)
Cadmium, with the chemical symbol Cd, is a soft, silvery-white, ductile, and malleable transition metal. It is located in Group 12 and Period 5 of the periodic table. While not as widely known as some other metals, cadmium is a significant element, though recognized for its toxicity. In India, cadmium is primarily obtained as a byproduct during the refining of zinc ores, for instance, from operations like Hindustan Zinc, which processes zinc-lead deposits.
Fundamental Atomic Particles of Cadmium
The atomic structure of Cadmium can be understood by examining its constituent subatomic particles: protons, neutrons, and electrons.
Atomic Number and Protons
The atomic number (Z) of Cadmium is 48. The atomic number directly corresponds to the number of protons in the nucleus of an atom. Therefore, a neutral Cadmium atom contains 48 protons. Protons carry a positive electrical charge.
Electrons
In a neutral atom, the number of electrons is equal to the number of protons to maintain electrical neutrality. Since Cadmium has 48 protons, a neutral Cadmium atom possesses 48 electrons. Electrons carry a negative electrical charge and occupy specific energy levels or shells surrounding the nucleus.
Neutrons
The number of neutrons in an atom can vary, leading to different isotopes of an element. The mass number (A) represents the total number of protons and neutrons in the nucleus. The most abundant isotope of Cadmium is Cadmium-114 ($^{114}$Cd).
To calculate the number of neutrons: Number of neutrons = Mass number (A) - Atomic number (Z) Number of neutrons = 114 - 48 = 66 neutrons
Therefore, the most common Cadmium atom has 48 protons, 48 electrons, and 66 neutrons.
Electron Configuration of Cadmium
Electron configuration describes the arrangement of electrons in the atomic orbitals of an atom. For Cadmium (Z=48), the electrons fill the orbitals according to the Aufbau principle, Hund’s rule, and Pauli exclusion principle.
The full electron configuration for Cadmium is: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰
A more condensed form, using the noble gas configuration, replaces the core electrons with the symbol of the preceding noble gas. For Cadmium, the preceding noble gas is Krypton (Kr), which has an atomic number of 36. Its configuration is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶.
Thus, the noble gas electron configuration for Cadmium is: [Kr] 4d¹⁰ 5s²
This configuration shows that after the Krypton core, there are 10 electrons in the 4d subshell and 2 electrons in the 5s subshell. The 4d subshell is completely filled, indicating a stable arrangement for these inner d-electrons.
Valence Electrons of Cadmium
Valence electrons are the electrons in the outermost shell of an atom. These electrons are primarily involved in chemical bonding and determine an element’s chemical properties.
From the electron configuration [Kr] 4d¹⁰ 5s², the outermost principal energy level (shell) is n=5. The electrons in this shell are the 5s² electrons.
Therefore, Cadmium has 2 valence electrons. These two 5s electrons are relatively easily removed, which explains why Cadmium typically forms compounds in which it exhibits a +2 oxidation state. The completely filled 4d subshell contributes to the stability of the Cd²⁺ ion.