NCERT & CBSE Class 11 Chemistry MODERN PERIODIC TABLE
Class 11 chemistry classes: Modern periodic law(given by Mosley) states that there is a periodic repetition of properties of the elements is arranged in order of their increasing atomic numbers. This law is the basis of formulation of the modern periodic table of elements. Many other chemists also arranged different elements in order of increasing atomic numbers. This periodic table is also known as a Long or Extended form of Periodic Table.
The present form of a periodic table which is widely used across the globe is the long form of the periodic table. In this form of a periodic table, the horizontal rows are called periods and the vertical columns are known as the groups.
The repetition of properties of elements results from alike outer electronic configuration after certain regular intervals. The elements of group IA are alkali metals which have a similar outer electronic configuration, i.e. ns1 where n refers to the number of outermost shells (principal quantum number).
Long Form of Periodic Table
The long form of the periodic table is built according to the electronic configuration of the elements. It is the present form or the modern periodic table of elements. The modern periodic table of elements consists of 18 vertical columns (groups) and 7 horizontal rows (periods). The elements with similar electronic configuration are placed in the same vertical column(groups) under one another.
Groups in the Periodic Table
- There are 18 vertical columns or groups (numbered from 1-18)in the modern or long form of the periodic table.
- Each of the group consists of elements having the same electronic configuration of the outermost shell.
- The groups are arranged as IA, IIA, IIIB, IVB, VB, VIB, VIIB, VIII, IB, IIB, IIIA, IVA, VIIA and 0
- The elements of subgroups IB, IIB………..VIIB and VIII group are called normal or representative elements. These elements have their outermost shells incomplete, whereas the rest shells are complete.
- The elements of the zero group are called inert elements. They have all their shells complete and are placed to the extreme right of the table.
Periods in the Periodic Table
- There are 7 periods in the long form of the periodic table. These periods are short and long.
- These are numbered as 1, 2, 3, 4, 5, 6 and 7 from top to bottom.
- The first period (very short period) consists of only two elements – Hydrogen (H) and Helium (He).
- The 2nd and 3rd period (short period) consists of 8 elements each. On the other hand, the 4th and 5th and 6th period (called long period) consists of 18, 18 and 32 elements respectively. The 6th period includes an additional 14 elements called rare earth elements or lanthanides (atomic numbers from 58-71)
- The 7th period is an incomplete period containing 23 elements only of which there are 14 actinide elements (atomic numbers 90- 103). These actinide elements are radioactive.
- The elements after Uranium (atomic number 92) are known as transuranic elements. These elements are all synthetic elements resulting from atomic research.
- The lanthanides and actinides are placed below the main part of the periodic table
Thus, the total number of elements discovered so far is 109. There are many more elements still to be discovered.
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