periodic trends in properties of element –atomic radee

When comparing the properties of the chemical elements, recurring ('periodic') trends are apparent. This led to the creation of the periodic table as a useful way to display the elements and rationalize their behavior. When laid out in tabular form, many trends in properties can be observed to increase or decrease as one progresses along a row or column.

These period trends can be explained by theories of atomic structure. The elements are laid out in order of increasing atomic number, which represents increasing positive charge in the atomic nucleus. Negative electrons are arranged in orbitals around the nucleus; recurring properties are due to recurring configurations of these electrons.

These periodic trends are distributed among 3 different properties, namely physical properties, chemical properties and on the basis ofchemical reactivity. In chemical properties, it is classified on the basis of two; i.e. periodicity of valence or oxidation states, anomalous properties of second period elements. In this article the periodic trends with respect to their physical properties are briefly discussed.

Atomic radius

• Covalent radius: half the distance between two atoms of a diatomic compound, singly bonded.

• Van der Waals radius: half the distance between the nuclei of atoms of different molecules in a lattice of covalent molecules.

• Metallic radius: half the distance between two adjacent nuclei of atoms in a metallic lattice.

• Ionic radius: half the distance between two nuclei

When two atoms are combined together then we can estimate their atomic size by checking the distance between the atoms. The other method by which we can measure the atomic size of a non-metallic element is by forming 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 metallic radius. It is defined as half of the total distance between the nuclei of two adjoining metal ions joined together by a metallic bond. 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. We can explain this trend by considering the nuclear charge and energy level. In general, atomic radius decreases as we move from left to right in a period and it increases when we go down a group. This is because 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.