Atomic Radii and Ionic Radii

Regular patterns in the properties of chemical elements are revealed by the periodic table of elements, which is a representation of their attributes.The periodic trends of electronegativity, ionization energy, electron affinity, atomic radii, ionic radius, metallic character, and chemical reactivity are just a few examples of the major periodic patterns. The distance between the nucleus’s center and the outermost shell, which contains electrons, is measured in atomic radius. For the sake of simplicity, we’ll refer to it as the distance between the nucleus’s core and a point at which the density of the electron cloud is at its highest.

Types of atomic radius 

• Covalent radius 

• Van der Waals radius 

• Metallic radius 

Covalent radius 

Molecular covalent radius is half the distance between the nuclei of two covalently bound atoms of the same element that are found in a molecule, and it is defined as As a result, the covalent constant rcovalent = 1/2 (internuclear distance between two bonded atoms). The bond length is the distance between two bonded atoms that exists between their nuclei. Therefore,

rcovalent  = 1/2 (bond length) 

Van der Waals radius 

Whenever the electrostatic forces between two unbonded atoms are equal and balanced, the Van der Waals radius is equal to one-fifth the distance between the two atoms. In other words, it is half of the shortest distance between two atoms that are not linked together or that are not part of the same molecule as one. Picometers (pm) are the units of measurement most commonly used to report the value. When intermolecular forces (such as dipole-dipole and dispersion forces) are active, the distance between them reflects the action of these forces and is connected to van der Waals interactions. Knowing the van der Waals radius can be quite useful when forecasting how closely atoms will pack together to create a solid.

Metallic radius 

If you look at a metal lattice or crystal, it is made up of positive kernels, which are metal ions that are organized in a specific pattern among a sea of mobile electrons. Each kernel is attracted by a number of mobile electrons at the same time, and each mobile electron is attracted by a number of metal ions at the same time as well.

The metallic bond is a force of attraction between mobile electrons and positive kernels that is formed when the electrons interact with the positive kernels. In the metallic lattice, it is one-half the internuclear distance between two adjacent metal ions, and it is one-half the distance between two adjacent metal ions in the crystal structure. The valence electrons in a metallic lattice are mobile, and as a result, they are only weakly attracted by the metal ions or kernels in the lattice.

In a covalent bond, a pair of electrons is firmly attracted to the nuclei of two different atoms by the force of attraction. A metallic radius is always greater than its covalent radius, as a result of this. Examples include sodium, which has a metallic radius of 186.5 pm, and a covalent radius of 154 pm determined by its vapor, which may be found in the form of Na₂. Potassium has a metallic radius of 231 pm and a covalent radius of 203 pm, indicating that it is a transition metal.

Ionic radii 

The ionic radius is the distance between the ions of an atom in a crystal lattice. It is equal to half of the distance between two ions that are barely touching each other in space. Because the boundary of an atom’s electron shell is rather ambiguous, the ions are frequently regarded as if they were solid spheres fixed in a lattice.

Trends in ionic radii 

Ions can be either larger or smaller than a neutral atom, depending on how much charge is attached to the ion. In the case of an atom that has lost an electron in order to form a cation, the lost electron is no longer contributing to shielding the other electrons from the charge of the nucleus; as a result, the other electrons are more strongly attracted to the nucleus, and the radius of the atom shrinks as a result. Additionally, when one electron is added to an atom, resulting in the formation of an anion, the additional electron repels the addition of other electrons, causing the atom’s size to expand.

The ionic radius of a specific ion is not a fixed feature; rather, it fluctuates depending on the coordination number, spin state, and other properties of the ion. We are assuming the ions to be in a state that is as near to their ground state as possible for our purposes. In spite of this, the values of ionic radius are sufficiently transferrable to allow for the recognition of periodic trends.

Conclusion 

Knowing the van der Waals radius can be quite useful when predicting how closely atoms will pack together to create a solid. The metal bond is a force of attraction between mobile electrons and positive kernels that are formed when the electrons interact with the ions in a lattice. In a covalent bond, a pair of electrons is attracted to the nuclei of two different atoms by the force of attraction. Examples include sodium, which has a metallic radius of 186.5 pm determined by its vapor, and potassium, which may be found in the form of Na₂.