Shielding Effect and Effective Nuclear Charge for JEE

In this article, we will be discussing some of the most important concepts of atomic and modern chemistry, shielding effect and effective nuclear charge. We will start by introducing you to the definition of concepts. After that, we will discuss concepts in detail. Understanding the shielding effect and effective nuclear charge can help us to create compounds that are less reactive and more stable. In this article, we are going to discuss the 3 important topics. They are Effective Nuclear Charge, Shielding effect, and Slater's Rules. So buckle up for an exciting ride into the fascinating world of atomic and modern Chemistry!

What is Effective Nuclear Charge?

The effective nuclear charge is the net positive charge experienced by an electron in an atom. It is a measure of the attractive force between the nucleus and the electron. The higher the effective nuclear charge, the greater the attraction between the nucleus and electron, and thus, the more tightly bound the electron is to the nucleus.

The effective nuclear charge can be calculated using various methods, but one common method is to use Slater's rules. According to these rules, the effective nuclear charge for an electron in an atom is equal to Z - S, where Z is the atomic number of the element (the number of protons in its nucleus) and S is calculated by the number of electrons between the nucleus and the electrons.

The effective nuclear charge plays an important role in determining many properties of atoms and molecules, such as ionisation energy, electronegativity, and atomic radius.

Effective Nuclear Charge

Slater's Rules

• Write the electron configuration for the atom using the following design:

(1s)(2s,2p)(3s,3p) (3d) (4s,4p) (4d) (4f) (5s,5p)

• Any electrons to the right of the electron of interest contribute no shielding. 

• All other electrons in the same group as the electron of interest shield to an extent of 0.35 nuclear charge units. Except the 1s which shield 0.30.

• If the electron of interest is an s or p electron: All electrons with one less value of the principal quantum number shield to an extent of 0.85 units of nuclear charge. All electrons with two less values of the principal quantum number shield to an extent of 1.00 units.

• If the electron of interest is an d or f electron: All electrons to the left shield to an extent of 1.00 units of nuclear charge.

• Sum the shielding amounts from steps 2 through 5 and subtract from the nuclear charge value to obtain the effective nuclear charge.

How to Calculate Effective Nuclear Charge

Below mentioned steps are used to calculate the effective nuclear charge.

Step 1: Find Atomic Number to Determine Z Value.

Step 2: Write the Electron Configuration.

Step 3: Attribute a Shielding Value to Each Electron.

Step 4: Sum the S Values.

Step 5: For result, use Effective Nuclear Charge Formula.

Effective Atomic Number (EAN)

The total number of electrons present with a central metal atom or ion in a coordination complex plus the electrons donated by the ligands is known as the Effective Atomic Number (EAN). By using EAN, we can find the stability of the metal in coordination complexes. If the EAN of any metal in the coordination complex is equal to the electrons of noble gases, then we can say that the particular complex is more stable.

Effective Atomic Number Formula = Z−O.N+2 C.N

Z = Atomic number

O.N= Oxidation number

C.N = Coordination number

What is the Shielding Effect?

In an atom, electrons can shield each other from the pull of the nucleus. This effect, called the shielding effect, describes the decrease in attraction between an electron and the nucleus in any atom with more than one electron shell. The more electrons are present, the greater the shielding effect experienced by the outermost electrons.

The net force on the electron in hydrogen-like atoms with only one electron is as strong as the electric attraction from the nucleus. When there are more electrons involved, each electron (in the n-shell) experiences both electromagnetic attractions from the positive nucleus and repulsion forces from other electrons in shells ranging from 1 to n-1. As a result, the net electrostatic force on electrons in outer shells is much smaller in magnitude. As a result, electrons away from the nucleus are not as strongly bound as those which are close to the nucleus.

The shielding effect explains why electrons in the valence shell are more easily removed from the atom. When the attraction is strong, the nucleus can pull the valence shell in tighter, and less tight when the attraction is weak. The greater the shielding, the further the valence shell can spread. As a result, atoms will grow in size.

Important Points

• Silicon has 4 valence electrons and therefore has a net effective charge of +4.

• Bromine has 7 valence electrons and net effective nuclear charge is +7.

• The electronic configuration of potassium shows that potassium ions have three shells and the last shell has eight electrons. The effective nuclear charge of 4s electron in potassium is 2.20.

Summary

In this article, we learned about two concepts, i.e., Shielding Effect and Effective Nuclear Charge. Shielding refers to the core electrons repelling the outer electrons, which lowers the effective charge of the nucleus on the outer electrons. Hence, the nucleus has "less grip" on the outer electrons as it is shielded from them. The effective nuclear charge is the net positive charge experienced by an electron in a multi-electron atom. The term "effective" is used because the shielding effect of negatively charged electrons prevents higher orbital electrons from experiencing the full nuclear charge.