Chemical And Physical Properties Of Periodic Elements

Modern periodic table arranges the elements in the order of their atomic numbers in seven horizontal rows (periods) and eighteen vertical columns (groups or families).Atomic numbers in a period are consecutive, whereas in a group they increase in a pattern.

Four types of elements can be recognized in the periodic table on the basis of their electronic configurations. These are s-block, p-block, d-block and f-block elements.

The physical and chemical properties of elements vary periodically with their atomic numbers.

Physical Properties:

There are numerous physical properties of elements such as melting and boiling point, heat of fusion and vaporization etc which show periodic variations

Periodic trends are observed in the atomic sizes, ionization enthalpies, electron gain enthalpies, electro-negativity and valence. The atomic radii decrease while going from left to right in a period and increase with atomic number in a group. Ionization enthalpies generally increase across a period and decrease down a group. Electro-negativity also shows a similar trend. Electron gain enthalpies, in general become more negative across a period and less negative down a group. There is some periodicity in valence, for example, among representative elements, the valence is either equal to the number of electrons in the outermost orbitals or eight minus this number

Metals comprise more than seventy eight per cent of the known elements. Non-metals which are located at the top of the periodic table are less than twenty in number. Elements which lie at the border line between metals and non-metals (e.g Si, Ge, As) are called as metalloids or semi-metals. Metallic character increases with increasing atomic number in a group whereas decreases from left to right in a period.

Chemical Properties:

Elements of the same group have similar valence shell electronic configuration and therefore exhibit similar chemical properties.

Chemical reactivity is highest at the two extremes of a period and is lowest in the centre. The reactivity on the highest at the two extremes of a period and is lowest in the centre. The reactivity on the left extreme of a period is because of the ease of electron loss (or low ionization enthalpy).Highly reactive elements usually occur in the combined form and not in their free state .Oxides formed of the elements on the left are basic and of the elements on the right are acidic in nature. Oxides of elements in the centre are amphoteric or neutral.

Periodicity of valence or oxidation states is observed in the valence of elements –hydrides and oxides. There are many elements which exhibit variable valence and this is particularly characteristic of transition elements and actinoids. Anomalous properties of second period elements are observed which is attributed to their small size, large charge/radius ratio and high electro-negativity.

Thus, periodic trends are observed in certain fundamental properties such as atomic and ionic radii etc which is related to electronic configuration. That is, all chemical and physical properties are a manifestation of the electronic configuration of elements.