Trends and Periodic Variation of Elements in the Periodic Table

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Atomic Radius

Atomic Radius is one-half the distance between two nuclei in two adjacent identical atoms and is measured in terms of picometer (pm)

Atomic radius could either be metallic radius or covalent radius. Metallic radius is a term used for the atomic radius of metallic elements while covalent radius is a term used for the atomic radius of nonmetallic elements.

The atomic radius can be identified by the strength of attraction of the nucleus of an atom and the outermost or valence electrons.

The strength of attraction is called nuclear charge.

The larger the value of the nuclear charge of an atom, the smaller is its atomic radius.

Larger nuclear charge indicates that the hold of the nucleus on the outermost or valence electron is strong.

The larger the value of the valence electron, the larger is the nuclear charge of the atom and the smaller is its atomic radius.

Atomic radius increases from top to bottom or down a group of the Periodic Table and decreases from left to right or across a period of the Periodic Table.

Ionic Radius

Ionic radius is the radius of a cation or an anion in an ionic compound.

An atom tends to change in size as it becomes a cation or anion.

Metals give up electrons to form a positively charged ion (cation).

Nonmetals gain electrons to form a negatively charged ion (anion).

An atom gives up or gains electrons to be stable.

As metal forms a cation, its radius decreases because of a lesser electron-electron repulsion which is a result of the removal of electron. Therefore, a cation has a smaller ionic radius compared with anion.

As nonmetal forms an anion, its radius increases because of a greater electron-electron repulsion which is a result of the addition of electrons. Therefore, an anion has a bigger ionic radius compared with a cation.

Ionization Energy

Ionization energy is the minimum energy required to remove an electron from an isolated atom or ion in its ground state and is usually measured in terms of kilojoules per mole (kJ/mol).

One electron is removed from the atom one at a time.

When one electron in an atom is removed, the energy needed is called first ionization energy.

Metals have low ionization energies compared with nonmetals that is why metals readily give up electrons forming a cation.

Ionization energy increases from left to right or across a period of the Periodic Table and decreases from top to bottom or down a group of the Periodic Table.

Electron Affinity

Electron Affinity is the energy change when an atom in its ground state gains an electron forming an anion and is usually measured in terms of kilojoules per mole (kJ/mol).

Nonmetals have high electron affinity that is why nonmetals always form an anion.

Electron affinity increases from left to right or across a period of the Periodic table and from bottom to top or up a group of the Periodic Table.

Electronegativity

Electronegativity is the ability of an atom in a chemical bond to attract electrons toward it and is usually measured in terms of electronvolt (eV).

Electronegativity is related to ionization energy and electron affinity.

High electron affinity would mean a greater ability to pick up electrons easily while high ionization energy would mean a lesser possibility to loose an electron.

If an atom has high ionization energy and high electron affinity therefore it also has high electronegativity.

Electronegativity increases from left to right or across a period of the Periodic Table and it decreases from top to bottom or down a group of the Periodic Table.

Metallic Character

Metallic character is a chemical property associated with elements classed as metals.

These are elements that have the tendency to give up electrons and form positive ion.

In the Periodic Table, metallic character increases down any group and across a period from right to left.

Nonmetallic Character

Nonmetallic character is a chemical property associated with elements classed as nonmetals.

These are elements that have the tendency to gain electrons and form negative ion.

In the Periodic Table, nonmetallic character increases up any group and across a period from left to right.

In a nutshell