Question:

Effective nuclear charge $\left(Z_{eff} \right)$ for a nucleus of an atom is defined as

Updated On: Aug 1, 2023

shielding of the outermost shell electrons from the nucleus by the innermost shell electrons
the net positive charge experienced by electron from the nucleus
the attractive force experienced by the nucleus from electron
screening of positive charge on nucleus by innermost shell electrons.

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The Correct Option is B

Approach Solution - 1

Effective nuclear charge is the net positive charge experienced by the electrons from the nucleus. Due to presence of electrons in the innermost shells the electrons in the outermost shell do not experience the full positive charge from the nucleus. This is known as shielding of the outermost shell electrons from the nucleus by the innermost shell electrons.

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Approach Solution -2

Effective nuclear charge is the net positive charge experienced by the electrons from the nucleus. It is the nuclear charge that is experienced by the electron. The strength of the nuclear charge can be found out by the oxidation number of the atom. It can be defined as the measure of the electrostatic interaction between the negatively charged electrons and the positively charged protons.

The electrons with the lowest energy are the ones that occupy the closest to the nuclear and the one with the higher energy occupy the father shells. The formula for effective nuclear charge can be given by,

Zeff = Z-S

Where, Z= atomic number

S=number of shielding electron

In a periodic table:

The Zeff increases across a period because of the increase in the nuclear charge although there is no increase in shielding effect.

Decreases down the group due to the increase in shielding effect.

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Notes on Structure of atom

Concepts Used:

Structure of Atom

Atomic Structure:

The atomic structure of an element refers to the constitution of its nucleus and the arrangement of the electrons around it. Primarily, the atomic structure of matter is made up of protons, electrons and neutrons.

Dalton’s Atomic Theory

Dalton proposed that every matter is composed of atoms that are indivisible and indestructible.

The following are the postulates of his theory:

Every matter is made up of atoms.
Atoms are indivisible.
Specific elements have only one type of atoms in them.
Each atom has its own constant mass that varies from element to element.
Atoms undergo rearrangement during a chemical reaction.
Atoms can neither be created nor be destroyed but can be transformed from one form to another.

Cons of Dalton’s Atomic Theory

The theory was unable to explain the existence of isotopes.
Nothing about the structure of atom was appropriately explained.
Later, the scientists discovered particles inside the atom that proved, the atoms are divisible.

Subatomic Particles

Protons - are positively charged subatomic particles.
Electron - are negatively charged subatomic particles.
Neutrons - are electrically neutral particles and carry no charge

Atomic Structure of Isotopes

Several atomic structures of an element can exist, which differ in the total number of nucleons.These variants of elements having a different nucleon number (also known as the mass number) are called isotopes of the element. Therefore, the isotopes of an element have the same number of protons but differ in the number of neutrons. For example, there exist three known naturally occurring isotopes of hydrogen, namely, protium, deuterium, and tritium.