Periodic Table
Chemistry SSc
Periodic table is the outstanding collection of chemical concepts gathered over hundreds of years. Various scientists have given their tireless effort after it to get the present state of the table.
Characteristics of the Periodic Table:The periodic table is basically a table of elements. It also features columns and rows. In the periodic table, the rows from left to right are called Periods and vertical columns are called Groups.
The modern periodic table has some prominent characteristics.a) There are seven periods (horizontal rows) and 18 groups (vertical columns) in the periodic table.b) All periods start with group 1 at the extreme left and extend up to group 18 at the extreme right.c) A small table of 2 horizontal rows and 14 columns displays the lanthanide and actinide elements beneath the main periodic table. These are part of period 6 -7 of main periodic table.d) Period 1 contains only two elements. Periods 2 and 3 contain four elements each. Periods 4 and 5 contain 18 elements each. Periods 6 and 7 contain 32 elements each.e) Group 1 contains 7 elements. Group 2 contains 6 elements. Group 3 has 32 elements. Groups 4 to 12 contain 4 elements each. Groups 13 -17 have 6 elements each. Group 18 contains 7 elements.Fifteen elements with atomic numbers 57 to 71 are called Lanthanide elements. Fifteen elements with atomic numbers 89 to 103 are categorized as Actinide elements.Now consider the periodic table in terms of properties of elements.1. Properties of elements change from left to right in the same period.2. The physical and chemical properties of elements of the same group are almost similar.
Determining the Period Number:the number of the outermost main energy level in the electronic configuration of an element is the period number of that element.For example, the electronic configuration of Lithium is Li(3) --> 1s²2s¹. Since the outermost energy level of Lithium is the second one, so the element belongs to the period 2 of the table.
Some Exceptions of the Periodic Table:
a. The Position of Hydrogen:
Hydrogen is a non-metal. However, the periodic table displays hydrogen alongside strong electropositive alkali metals like Na, K, Rb, Cs, Fr etc. in group 1. It is because the outer shell of H contains only 1 electron like the alkali metals. Besides, many properties of hydrogen are similar to those of alkali metals. On the other hand, hydrogen also is able to accept an electron like the halogen elements (F, Cl, Br, I), meaning it has some similarities with Halogen in terms of properties. However, since most of the properties of hydrogen in terms of properties. However, since most of the properties of Hydrogen have similarity with alkali metals, it is placed alongside alkali metals.
b. The Position of Helium
c. The Position of Lanthanide and Actinide Groups