Ionic Radius

Ionic radii, what is it? Let’s figure out what we mean by ionic radii and their variation in groups and periods of the periodic table (modern eriodic table).

What is Ionic Radius?

Ionic radius is the distance from the nucleus of an ion up to which it has an influence on its electron cloud.

Ions are formed when an atom loses or gains electrons. When an atom loses an electron it forms a cation and when it gains an electron it becomes an anion. The Ionic radius can be described as the distance between the nucleus of an ion and the outermost shell of the ion.

The atomic size of a cation will be smaller than that of the parent atom. An anion is relatively larger in size than its parent atom. This is because when an atom gains electrons the total number of electrons increases which tends to create more repulsion between electrons and thus overshadows the net effective nuclear charge.

Ionic Radius Periodic Table

Periodic Trends

For example,

  • Radius of potassium = 243pm.
  • Radius of potassium ion = 138pm.

Atoms and ions which consist of an equal number of electrons are considered isoelectronic species. For example, Both O2-, Mg2+ have 10 electrons but they don’t have the same ionic radius as the effective nuclear charge in both of them is different.

The radius of a cation will be smaller than that of the anion as a cation will have a greater positive charge (i.e. number of protons) so it will attract the electrons in the outermost orbital with greater force and hence the smaller size.

Trends in Ionic Radius in Groups

In a periodic table while moving down in a group, atoms add an extra shell (number of electrons) due to which the ionic radius of elements increases down a group.

Ions Configuration Ionic radii(nm) Ions Configuration Ionic radii(nm)
Li+ 2 0.076 F 2,8 0.133
Na+ 2,8 0.102 Cl 2,8,8 0.181
K+ 2,8,8 0.138 Br 2,8,18,8 0.196

Trends in Ionic Radius Across a Period

Let us understand the trends in the ionic radius of elements across a period with an example. In period 3 we find that the atomic radius first decreases and then suddenly increases and then again it slowly decreases. This is because the starting elements in a period tend to form cations, and the elements towards the end of a period tend to form anions.

Trends in ionic radii of ions in period 3

Period 3 Na2+ Mg2+ Al3+ P3- S2- Cl
Number of protons 11 12 13 15 16 17
Electronic configuration 2,8 2,8 2,8 2,8,8 2,8,8 2,8,8
Ionic radius 0.102 0.072 0.054 0.212 0.184 0.181

Ions are formed as a result of the gain or loss of electrons. The formation of ions plays a vital role in any chemical reaction to form a new substance. By knowing the ionic radii we can study various chemical bonds formed during a reaction.

Recommended Videos

Frequently Asked Questions

Q1

Define atomic radius.

Atomic radius is the mean or typical distance from the centre of the nucleus to the boundary of the surrounding shells of electrons.
Q2

Define ionic radius.

Ionic radius is the distance from the nucleus of an ion up to which it has an influence on its electron cloud.
Q3

Define cation and anion.

When an atom loses an electron it forms a cation and when it gains an electron it becomes an anion.
Q4

What are isoelectronic species?

Atoms and ions which consist of an equal number of electrons are considered electronic species.
Q5

Why the size of the anion is larger than the parent atom?

An anion is relatively larger in size than its parent atom. This is because when an atom gains electrons the total number of electrons increases which tends to create more repulsion between electrons and thus overshadows the net effective nuclear charge.

To know more about elements of the periodic table and its properties visit BYJU’S.

Test your knowledge on periodic trends in ionic radii in modern periodic table

Comments

Leave a Comment

Your Mobile number and Email id will not be published.

*

*