The periodic table is an arrangement of the chemical elements, organized on the basis of their atomic numbers, electron configurations and recurring chemical properties.
We are presently aware of only 118 elements. But it is said that there are more elements that are waiting to be discovered.
Scientists had to devise ways to arrange these 118 elements, half of which were not even discovered back then. They wanted to arrange these elements in such a way that discovering as yet undiscovered elements would become easier, and studying the properties of these elements would become efficient.
Dmitri Mendeleev was the first chemist to arrange the elements in the periodic table on the basis of atomic weights in 1869. However, this method was not without fallacies as it didn’t take into account the atomic masses of the elements.
Henry Moseley later modified Mendeleev’s period table and classified the elements of the periodic table according to their atomic numbers instead of weights. This method of classifying elements did away with the errors that were prevalent in the previous periodic table made by classification based on atomic weights.
Henry Moseley’s is the periodic table we currently use.
Since Moseley arranged elements in the periodic table according to the Modern Periodic Law, the periodic table is known as Modern Periodic Table. The Modern Periodic Law states, ‘Physical and chemical properties of elements are periodic functions of their atomic numbers.’
Since the properties of an element depend on its electronic configuration, thus electronic configuration of elements is intrinsic to the Modern Periodic Table.
The periodic table correlates the position of an element with its electronic configuration.
The periodic table arranges elements in seven horizontal rows called periods in increasing order of their atomic numbers. The elements in a period share the same number of energy shells.
Completion of each period is logical since each period begins with an element having one electron in its outermost shell and ends with a zero or eighteen group elements having a completely filled outermost shell.
Thus, periods contain elements arranged in increasing order of their valence electrons from left to right. Thus a transition from metallic to non metallic character is seen across a period. Electro negative character increases from left to right in a period.
The period number tells us about the number of orbits the elements of a particular period has.
Elements are arranged in eighteen vertical columns called groups. Each group accommodates elements having the same electronic configuration and thus having similar properties.
Groups 1, 2 and 13 to 17 are called normal elements. Groups 1 and 2 contain highly reactive alkali metals and group 13 to 16 contain non metals. Group 17 contains non metals called halogens, the most electronegative elements.
Groups 3 to 12 contain transition elements. The period 7 and 8 of these groups contain inner transition elements called actinides and lanthanides.
Group 18 or 0 contains noble or inert gases.
Recurrence in properties is seen with elements belonging to the same subgroup in the periodic table after a difference of 2, 8, 18 or 32 in atomic numbers due to recurrence of similar valence shell electronic configuration. Thus, we can easily know the properties of other elements of a group if we know the properties of even two elements of the same group. It consequently becomes easier to discover unknown elements.
The number of energy shells increase from up to down in a group. The metallic character and electro positivity increase in a group from up to down.
The number of valence electrons present in a group depends on its group number. Elements of group one have one valence electron whereas Group 17 (VII A) contains 7 valence electrons.