Modern Periodic Table Of Elements

Modern Periodic table

Who is given the modern periodic table? A more detailed classification of the elements is the one devised by Dmitri Mendeleev in 1869; this scheme is familiar to every chemist as the periodic table. Mendeleev arranged the known elements in order of increasing atomic weight (molar mass). This arrangement resulted in families of elements with similar chemical properties, which he arranged into the groups of the periodic table.

For example, the fact that C, Si, Ge, and Sn all form hydrides of the general formula EH4 suggests that they belong to the same group. That N, P, As, and Sb all form hydrides with the general formula EH3 suggests that they belong to a different group.

Other compounds of these elements show family similarities, as in the formulas CF4 and SiF4 in the first group, and NF3 and PF3 in the second.

Mendeleev concentrated on the chemical properties of the elements. At about the same time Lothar Meyer in Germany was investigating their physical properties and found that similar values repeated periodically with increasing molar mass.

Long Form Of Periodic Table Or Modern Periodic Table

The Modern Periodic Table or the Long Form of Periodic Table is a periodic table (given by Bohr) in which the arrangement of the elements has been made on the basis of the atomic number of the elements, which is a more fundamental property of the elements.

In the modern periodic table, the arrangement of elements has been made in accordance with Mosley’s periodic law, i.e. the elements have been grouped in the increasing order of their atomic number.

The modern periodic table is also called Bohr’s periodic table, since it is based on Bohr’s scheme ofclassification of elements into four types, demanding on the number of incomplete shells in the atom.

The Modern Periodic Law states that the physical and chemical properties of elements are the periodic function of their atomic numbers.

The vertical columns of the periodic table are called groups or families or simply columns, while the horizontal rows in the table are called periods or simply rows.

Modern Periodic table

Groups 

There are 18 vertical columns in the modern periodic table. In terms of electronic configurations of the atoms of the elements, a group consists of elements whose atoms have the same outermost electronic configuration. There are two systems of numbering the groups.

According to the recommendations of IUPAC, the groups renumbered as 1, 2, 3,…….17, 18 while according to another system, the groups are named as IA (for 1), IIA (2), IIIB (3), IVB (4), VB (5), VIB (6), VIIB (7), VIIIB (8,9,10), IB (11), IIB (12), IIIA (13), IVA (14), VA (15), VIA (16), VIIA (17), and VIIIA (18) are called p-block elements. s- and p-block elements taken together are called main group elements.

The elements of groups IA (for 1), IIA (2), IIIB (3), IVA (14), VA (15), VIA (16), and VIIA (17) are called representative elements and those of group VIII A (18) are called noble gases.

The elements belonging to groups IIIB (3), IVB (4), VB (5), VIB (6), VIIB (7), VIIIB (8,9,10), IB (11), and IIB (12) (ten vertical columns) are called d-block or transition elements.

There are two rows of elements that have been placed separately at the bottom of the periodic table. Each row consists of 14 elements. Fourteen elements of 1st  row viz Ce58 to Lu71 are called 4f-block elements or lanthanides while 14 elements of the 2nd row viz Th90 to Lw103 are called 5f-block elements or actinides. 4f and 5f block elements are collectively called f-block elements or inner-transition elements or rare earth elements.

general structure of the periodic table

Periods

There are 7 periods in all. 7th period (last period) is an incomplete period, since it contains only 20 elements although it is expected to contain 2 + 10 + 14 + 6 = 32 elements. In each period the elements have been placed in the increasing order of their atomic number.

The first element of each period is an alkali metal and the last element is a noble gas. 1st, 2nd and 3rd periods contain 2, 8 and 8 elements respectively are called short periods while 4th, 5th  and 6th periods which contain 18, 18 and 32 elements are called long periods.

The elements of 2nd and 3rd periods were called typical elements by Mendeleev since he thought that these are the true representatives of their respective groups.

But, now since it has been found that the elements of 2nd period resemble more closely with the elements placed diagonally opposite to them than with the elements of their own groups, the elements of 2nd period are now not considered as true representative elements.

Nowadays the elements of 3rd period viz Na, Mg, Al, Si, P, S and Cl are called typical elements.

Superiority of Modern Periodic Table Over Mendeleev’s Table

Long-form of periodic table is superior to Mendeleev’s periodic table in the following respects:

The classification of the elements in the long form of the periodic table has been made on the basis of the atomic number of the elements, which is a more fundamental property of the elements.

The classification of the elements in the long form of periodic table has been made on the basis of the valence shell configurations of the elements, i.e., the elements having the same valence shell configurations have been placed in the same group.

The elements having ns1 and ns2 as their valence shell configurations have been placed in the extreme left portion of the periodic table [group IA (alkali metals) and group IIA (alkaline earth metals)], the elements having ns2np1-6 as their valence shell configurations have been placed in the extreme right portion of the periodic table (group IIIA to zero group), the elements having (n-1)d1-10 ns0-2 as their valence shell configuration (transitional elements)  have been placed just before III A group, the elements having the differentiating electron in their (n-2) f orbitals (i.e. lanthanides and actinides) have been placed between alkaline earth metals and transition elements.

The elements of the two sub-groups have been placed separately and thus dissimilar elements do not fall together.

This periodic table is easier to remember, understand and reproduce.

Defects of Modern Periodic Table

The problem of the position of hydrogen still remains unsolved. Like Mendeleev’s table, it fails to accommodate the lanthanides and actinides in the main body of the table.

What are the uses of modern periodic table?

Mendeleev provided a spectacular demonstration of the usefulness of the periodic table by predicting the general chemical properties—such as the numbers of bonds they form— of unknown elements such as gallium, germanium, and scandium corresponding to gaps in his original periodic table.

(He also predicted elements that we now know cannot exist and denied the presence of elements that we now know do exist, but that is overshadowed by his positive achievement and has been quietly forgotten.)

The same process of inference from periodic trends is still used by inorganic chemists to rationalize trends in the physical and chemical properties of compounds and to suggest the synthesis of previously unknown compounds.

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