In the field of chemistry, atomic radius refers to the measure of the distance from the nucleus of an atom to its outermost shell of electrons. It is considered an important part of understanding periodic trends, and it is essential for a deeper understanding of the properties of atoms and molecules. This article will explain why atomic radius decreases across a period.

Periodic Table of Elements

The periodic table of elements is an arrangement of elements in order of atomic number. Each element is placed in the table in order of increasing atomic number. Elements in the same column, known as groups, have similar properties due to the same number of valence electrons. Elements in the same row, known as periods, have similar properties due to the same number of atomic shells.

Atomic Structure

Atoms consist of a nucleus, which is made up of protons and neutrons, and an electron cloud, which consists of electrons in shells. The number of protons and electrons in an atom is equal and is called the atomic number. The number of protons in the nucleus determines the element, but the number of neutrons in the nucleus can vary, resulting in isotopes of the same element.

Atomic Radius

Atomic radius is the distance from the nucleus of an atom to its outermost shell of electrons. This value is determined by the number of protons and electrons in the atom as well as the number of shells. Since the atomic number increases across a period, the number of protons, electrons, and shells also increase. As a result, the atomic radius decreases across a period.

Electron Shielding

Another factor that contributes to the decrease in atomic radius across a period is electron shielding. Electron shielding is the effect of inner electrons shielding the outer electrons from the full attractive force of the nucleus. This effect is more pronounced in atoms with higher atomic numbers due to the additional inner shells of electrons. As a result, the outer electrons of atoms with higher atomic numbers are less attracted to the nucleus, resulting in a smaller atomic radius.

Effective Nuclear Charge

The effective nuclear charge is the net positive charge experienced by the outer electrons due to the protons in the nucleus. This charge increases across a period, since the number of protons increases. As a result, the outer electrons are increasingly attracted to the nucleus, causing the atomic radius to decrease.

Valence Electrons

Valence electrons are the electrons located in the outermost shell of an atom. The number of valence electrons increases across a period, since the number of shells increases. This increases the repulsion between the valence electrons, resulting in a decrease in the atomic radius.

Summary

In summary, atomic radius decreases across a period due to the increase in atomic number, electron shielding, effective nuclear charge, and the number of valence electrons. This decrease in atomic radius is an important part of understanding the periodic trends of the elements.