Periodic trends are the properties of periodic table elements which are largely untestable by the electronic configuration of elements. Electronegativity, ionization energy, electron affinity, atomic radii, ionic radius, metallic character, and chemical reactivity are the major periodic trends of chemical elements. The variation of such periodic trends is not smooth because several anomalies are appeared to explain such trends.
Size of the elements
When we moved left to right on the periodic table size of the elements and electropositive character decrease. Generally, descending down any group, the size of the atom and its electropositive character increase. Therefore metallic properties generally increase down groups and decrease from left to right on the periodic table.
Ionization energy trends
The value of ionization energy gradually increases in moving from left to right in a period. Since the nuclear charge of elements also increases in the same direction. The increase in the magnitude of ionization energy trends is due to increases in electrostatic attraction between outermost electrons and the nucleus. When we move from top to bottom in a group ionization energy of elements decrease with the increase of their atomic radii.
Many exceptions are come to explain the ionization energy trends of periodic table elements. For example, beryllium and nitrogen have higher ionization energy from their lower member lithium and carbon.
Electron affinity trends
In moving down a group, the electron affinity values are generally increasing. It is due to steady increases in the atomic radius of the elements. Many exceptions are come to explain such trends of electron affinity. For example, the elements of the second period are relatively smaller in size than the third period. Therefore, electron affinity values of second-period elements are smaller than the third-period elements. This unexpected periodic trend can be explained by the charge densities of elements.
On moving left to right in a periodic table, electron affinity values generally increase. Many exceptions are also come to explain such periodic trends of electron affinity along a period. For example, beryllium and magnesium have electron affinity values equal to zero due to the presence of completely filled s orbitals. Unexpected lower values of the electron affinity of nitrogen and phosphorus can be explained by their half-filled orbitals.
Electronegativity trends in the periodic table
Electronegativity increases on moving left to right in a period of the periodic table due to increases in nuclear charge. In moving down through a group of the periodic table nuclear change again increases, Therefore, the electronegativity of lower elements would be more than upper elements. In general small atoms attract electrons more strongly than large ones.