# Atomic Size & Atomic Radius, What is Atomic Size, Trends in the Periodic Table (For CBSE, ICSE, IAS, NET, NRA 2022)

Doorsteptutor material for competitive exams is prepared by world's top subject experts: get questions, notes, tests, video lectures and more- for all subjects of your exam.

# Title: Atomic Size & Atomic Radius

## What is Atomic Size?

• Atomic size is the distance between the centre of the nucleus of an atom and its outermost shell.
• In basic chemistry, the atomic radius is defined as the shortest distance between the atom՚s nuclei and the outermost shell of the atom.

• An atomic radius is half the distance between adjacent atoms of the same element in a molecule.
• Measuring the atomic radii of chemical elements is a complicated task as the size of an atom is of the order of . The electron cloud forming the shell of an atom does not have any fixed shape which makes it difficult to determine the atomic size of an atom. So, we can say that practically we cannot determine the size of an individual atom.
• Atomic radius is the distance from the centre of the nucleus to the outermost shell containing electrons. In other, it is the distance from the centre of the nucleus to the point up to which the density of the electron cloud is maximum.

## Trends in the Periodic Table

• When we move down a group of non-metals, the reactivity of the elements decreases while it increases with moving down the group in case of representative metals.
• When two atoms are combined, then we can estimate their atomic size by checking the distance between the atoms or we can measure the atomic size of a non-metallic element is by forming a single covalent bond between two atoms and checking the distance between the two atoms.
• The radius found by this method is known as the covalent radii of the element. In the case of metal, it is termed as a metallic radius. It is defined as half of the total distance between the nuclei of two adjoining metal ions joined by a metallic bond.
• The Atomic radius of an atom is measured by X-ray or other spectroscopy methods. The atomic radii of elements vary in the periodic table in a fixed pattern, this trend is explained by considering the nuclear charge and energy level.
• Atomic radius decreases as we move from left to right in a period and it increases when we go down a group as in periods the valence electrons are in the same outermost shell. The atomic number increases within the same period while moving from left to right which in turn increases the effective nuclear charge. The increase in attractive forces reduces the atomic radius of elements.

## Questions

### How Big is an Atomic Radius?

• Under most definitions the radii of isolated neutral atoms range between 30 and 300 pm (trillionths of a meter) , or between 0.3 and 3
• Therefore, the radius of an atom is more than 10,000 times the radius of its nucleus , and less than of the wavelength of visible light

### What Determines Atomic Size?

• Atomic size is the distance from the nucleus to the valence shell where the valence electrons are located.
• There are three factors that help in the prediction of the trends in the Periodic Table: number of protons in the nucleus, number of shells, and shielding effect.