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2.2 Introduction to the Periodic Table
The Periodic table is an arrangement of elements in the order of their increasing atomic numbers to show that elements have related properties. Earlier tables, such as those of Dmitry Mandeleev (photograph) (1869) and Lother Meyer (1869-70) were based on atomic weights which are measured as bulk properties and valency relationships. At that time the concept of atomic numbers was unknown. The main purpose of the periodic table was:
- Classification elements into groups with similar properties.
- To predict the possibilities of new elements based on their properties.
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The modern form of the periodic law states
that properties of the elements are the periodic function of their
atomic numbers and the properties of the elements depend on their
electronic configuration.
The modern periodic table consists of arrangements of elements in three broad categories.
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- metals (located on LHS)
- non-metals (located on RHS)
- metalloids ( in between) |
Understanding the Periodic Table :
The periodic table (Figure 2) arranges 109 known elements in order of their increasing atomic number. All these elements are arranged in Groups and Periods.
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Groups |
Periods |
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The vertical columns are called Groups.
Eight columns 1 to 7 column further divided into 'A' and 'B' 8 t h column not divided Group zero for noble elements Elements in each group have the same number of electrons in the outer shell and hence the same valency. Identical Chemical behavior for each group elements Lower down the group, number of shells increase by 1; hence atomic radius also increases. |
The horizontal rows are
called Periods.
Seven rows
No further division
6 t h period includes
Lanthanide series
7 t h period includes
Actinide series
Each period begin with an
alkali metal.
Number of electrons
increase by one, across
the period.
Elements change from
metals (Na) through semi-
metals (Si-Silicon) to non-
metals (Argon-Ar).
Elements change from
reducing agents (Na) to
oxidizing agents (Cl).
Number of shells remain
the same; atom size (radii)
decreases.
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