Question

State three points of difference between mendeleev's periodic table and modern periodic table.

Answer 1

The main differences are:

Mendeleev's periodic table is based on atomic mass. Modern periodic table is based on atomic number.

Mendaleev's periodic table contains about 66 elements. Modern periodic table contains presently 118 elements.

In Mendeleev's periodic table there were gaps for undiscovered elements.Modern periodic table maintains uniformity.

In Mendeleev's periodic table noble gases were not placed (as they are not discovered at that time).In Modern periodic table noble gases in a seperate group named as group-18.

In Mendeleev's periodic table transition elements included with other elements. In Modern periodic table transition elements placed in separate block.

According to Mendeleev's, the isotopes with different atomic weights, should be placed in different positions, but are not given any position and no justified reason was explained. In Modern periodic table, the isotopes were assigned same position as they have same atomic number.

Answer 2

Answer:

• Mendeleev's periodic table

1. elements are arranged in increasing order of their atomic masses.
2. It is not divided into any blocks.
3. There are 8 groups.
4. Isotopes could not be placed properly.

• Modern periodic table

1. Elements are arranged in increasing order of their atomic numbers.
2. It is divided into four blocks, namely s-block,p-block,d-block and f-block.
3. There are 18 groups.
4. Isotopes occupy the same position as the element.

Hope you understood mate!!!