Modern Periodic Table and Electronic Configuration of Elements (22)

Modern Periodic Table and Electronic Configuration of Elements
Within a period the neighbouring elements differ slightly in their properties while distant elements differ widely in their properties. Elements in the same group show similarity and gradation in their properties. These characteristics of the groups and periods in the modern periodic table are because of the electronic configuration of the elements. It is the electronic configuration of an element which decides the group and the period in which it is to be placed.
Characteristics of Groups and Periods
The characteristics of the groups and periods in the periodic table are understood by comparison of the properties of the elements. Various properties of all the elements in a group show similarity and gradation. However, the properties of elements change slowly while going from one end to the other (for example, from left to right) in a particular period.

1. Go through the modern periodic table and write the names one below the other of the elements of group 1.

→ The elements in the group 1 are:

Hydrogen
Lithium
Sodium
Potassium
Rubidium
Cesium
Francium

2. Write the electronic configuration of the first four elements in this group.

→ The electronic configurations of first four elements are given below:

Element	Atomic Number (z)	Electronic Configuration
H	1	1
Li	3	2, 1
Na	11	2, 8, 1
K	19	2, 8, 8, 1

3. Which similarity do you find in their configuration?

→ All the elements have 1 electron in their valence (outermost) shell.

4. How many valence electrons are there in each of these elements?

→ One.

You will find that the number of valence electrons in all these elements from the group 1, that is, the family of alkali metals, is the same. Similarly, if you look at the elements from any other group, you will find the number of their valence electrons to be the same. For example, the elements beryllium (Be), magnesium (Mg) and calcium (Ca) belong to the group 2, that is, the family of alkaline earth metals. There are two electrons in their outermost shell. Similarly, there are seven electrons in the outermost shell of the elements such as fluorine (F) and chlorine (Cl) from the group 17, that is, the family of halogens. While going from top to bottom within any group, one electronic shell gets added at a time. From this we can say that the electronic configuration of the outermost shell is characteristic of a particular group. However, as we go down a group, the number of shells goes on increasing.

Do you know?
Uranium has atomic number 92. All the elements beyond uranium (with atomic numbers 93 to 118) are manmade. All these elements are radioactive and unstable, and have a very short life.
In the modern periodic table ...
Elements are arranged in an increasing order of their atomic numbers. Vertical columns are called groups. There are 18 groups. The chemical properties of the elements in the same group show similarity and gradation. Horizontal rows are called periods. There are in all 7 periods. The properties of elements change slowly from one end to the other in a period.

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