Importance and Limitations of Modern Periodic Table

Importance of Modern Periodic Table

1. Based on atomic number –
The arrangement of elements in modern periodic table is according to their increasing order of atomic number. Atomic number increases by 1 unit (not fractional) in going from one element to the next element and equal to the number of electrons. Thus, the modern periodic table is easy to reproduce and remember than Mendeleev’s periodic table.

2. Prediction of new elements and properties –

Prediction of new element , position in periodic table and properties of new and other elements could be made with precision, when elements are arranged in order of increasing atomic number. This was not possible in Mendeleev’s periodic table as atomic masses never increase in a regular manner.

3. Justification of anomalous position of some pairs of elements –

Such as Co and Ni, Te and I etc. By arranging in order of increasing atomic number, these elements are arranged in groups having similar properties, which was the limitation of Mendeleev’s Periodic table.

4. Position of Isotopes –

Isotopes of an element have different atomic masses but same atomic number. Therefore, in Modern Periodic table, there is no confusion in their position as all isotopes of an element will be placed at one place due to same atomic number. For e.g. C12 , C13 and C14 – all three isotopes of carbon have same atomic number 12 and are placed in group 14 and 1st period.

Limitation of Modern Periodic Table

Hydrogen has no fixed position in modern periodic table similar to Mendeleev’s periodic table. Hydrogen can be placed either in group 1 or group 17 in the first period as it shows similarity in properties with both the groups.

The atomic number of an element never changes, meaning that the number of protons in the nucleus of every atom in an element is always the same. For example, all hydrogen atoms, and only hydrogen atoms, contain one proton and have an atomic number of 1. All carbon atoms, and only carbon atoms, contain six protons and have an atomic number of 6. Oxygen atoms contain 8 protons and have an atomic number of 8.
Atom’s mass number –
All atoms have a mass number which is derived as follows.
Number of neutrons + Number of protons = Mass number
An element’s or isotope’s atomic number tells how many protons are in its atoms.
An element’s or isotope’s mass number tells how many protons and neutrons in its atoms.