Introduction to Zinc (Zn)
Zinc is a silvery-white metallic element identified by the symbol Zn. It holds the atomic number 30 and belongs to Group 12 (the d-block elements or transition metals) and Period 4 of the periodic table. Zinc is an important industrial metal, with applications spanning various sectors. In India, zinc is significantly used in the galvanization of iron and steel to prevent rusting, a process common for roofing sheets and fences. It is also a key component in alloys like brass, traditionally used for making utensils and decorative items. Furthermore, zinc is an essential trace element for biological functions, found in many common Indian foods such as lentils, nuts, and whole grains.
Atomic Number and Mass Number of Zinc
The atomic number (Z) of an element represents the total number of protons present in the nucleus of an atom. For Zinc, the atomic number (Z) is 30. This means every neutral atom of Zinc contains 30 protons.
The mass number (A) refers to the total count of protons and neutrons in the nucleus of an atom. The most common isotope of Zinc is Zinc-65. Therefore, its mass number (A) is 65.
Number of Subatomic Particles in Zinc-65
For a neutral atom of Zinc-65:
- Number of Protons: The number of protons is equal to the atomic number.
- Protons = 30
- Number of Electrons: In a neutral atom, the number of electrons is equal to the number of protons to maintain electrical neutrality.
- Electrons = 30
- Number of Neutrons: The number of neutrons can be calculated by subtracting the atomic number from the mass number.
- Neutrons = Mass Number (A) - Atomic Number (Z)
- Neutrons = 65 - 30 = 35
Thus, a neutral atom of Zinc-65 contains 30 protons, 30 electrons, and 35 neutrons.
Electron Configuration of Zinc
Electron configuration describes the arrangement of electrons within the atomic orbitals of an atom. For Zinc, with 30 electrons, the electron configuration follows the Aufbau principle, Hund’s rule, and Pauli’s exclusion principle.
The full electron configuration for a neutral Zinc atom (Z=30) is: $1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10}$
Alternatively, using the noble gas notation, the condensed electron configuration is: $[Ar] 4s^2 3d^{10}$
This configuration indicates that the first 18 electrons fill the orbitals up to the configuration of Argon. The remaining 12 electrons then fill the 4s orbital completely (2 electrons) and subsequently the 3d orbital completely (10 electrons). The $3d^{10}$ configuration signifies a fully filled and stable d-subshell.
Valence Electrons of Zinc
Valence electrons are the electrons located in the outermost shell of an atom and are primarily involved in chemical bonding. For Zinc, despite the 3d subshell being filled after the 4s subshell, the 4s electrons are considered the valence electrons. This is because the 4s orbital is in the highest principal energy level (n=4) and is therefore the outermost shell.
Zinc has 2 valence electrons, located in the 4s orbital. These two electrons are readily lost during chemical reactions to form the stable $Zn^{2+}$ ion, which possesses a pseudo-noble gas configuration ($[Ar] 3d^{10}$). The completely filled 3d subshell contributes to the relative stability of the $Zn^{2+}$ ion.