Characteristics of Modern periodic table

Observe the following characteristics of Modern periodic table. It is helpful for the use of periodic table.

When we observe the Long form of periodic table naturally many questions arise.

There are only 2 elements in the first period. In second period there are 8 elements, why? Why are there only 7 periods? How to find the position of a particular element of definite mass number? What is the relationship between electronic configuration and periodic table? etc. Let us know about these things.

Note this

While writing (framing) the groups 'n' indicates outer most energy level, number (n-1) indicates penultimate energy level number (when'd' sub energy ievelexists).

Valence electrons, that is, electrons which participate in chemical reactions exists in ultimate and penultimate energy levels (when 'f sub energy level exists).

Let us remember the method of writing the electronic configuration. Is, 2s, 3s,... etc. While writing them the numbers written indicate energy levels. Such numbers are written from 1 to 7. In periodic table there are 7 horizontal rows.called 'Periods'. In this-periodic table, the elements are written in 18 vertical columns called 'Groups'. While writing the electronic configuration the number which indicates highest energy level will indicate the period to which that element belongs.

Let us find in which period chlorine is placed.

The atomic number of chlorine is 17. Its electronic configuration Is2, 2s2sp6, 3s23p5. The highest energy level is - 3. Hence chlorine is in the third period. Verify this calculation from the periodic table.

The vertical columns of the periodic table are called 'Groups'. Every group has its own generalised electronic configuration. There are 18 such groups. Now let us find out to

which group chlorine belongs whose atomic number is 17. Its third energy level is incomplete with 7 valence electrpns^ Its electronic configuration comes under ns np (generalization). Hence it belongs to 17th group.

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Observe the following examples.

Determine its validity from the periodic table. Determine the periods to which the following elements belong (on the basis of their electronic configuration) - Nitrogen, iodine, potassium, silver.

If we know atomic number and electronic configuration of an element we can find out to which group and period that element belongs. If we know about group and period, we can find out its position in the periodic table.

After finding the position of an element in the periodic table we can study different properties of that element which are written in that square.

Apart from this, on the basis of the position of element in the periodic table we can understand the properties of elements (and their compounds), properties of other similar elements and their compounds which belong to the same group.

It is quite interesting to study the graded properties of elements along the periods and groups.

Note this

Observe the electronic configuration of first group elements.

H - 1s1

Li - [He] 2s1

Na - [Ne] 3s1

K - [Ar] 4s1

Fib - [Kr] 5s1

CS - [Xe] 6s1

Fr - [Rn] 7s1

Generalisation — ns1 In this generalization the value of 'n' may be from 1 to 7.

Brain Teaser

Even though the electronic configuration of He is 1s2, instead of second group it is placed in the 18th group why? Think about it.

Activity

The atomic numbers of manganese, cadmium zirconium and silicon are 25, 48, 40 and 14 respectively. Write the electronic configuration of these elements and find out their groups and periods. Verify your answer with the help of periodic table.

Note this

While writing the electronic configuration highest energy level determines its period and incomplete orbit determines its group.

Modern periodic table features , what are the Modern periodic table features