What is a Periodic Table ?
Periodic Table is a tabular arrangement of elements, based on their electronic configurations, increasing atomic number and chemical proper
Need of Periodic Table ?
The periodic table is important because it is organized to provide a great deal of information about elements and how they relate to one another in one easy-to-use reference .It describes the atomic properties of every known chemical element in a concise format, including the atomic number, atomic mass and relationships between the elements. Elements with similar chemical properties are arranged in columns in the periodic table.
History of Periodic Table
- Dobereiner’s Triads – When elements are arranged in the order of their increasing atomic masses, the atomic mass of the middle element was approximately the average of the atomic masses of the other two elements. Eg – Li(6.9),Na(23),K(39)
- Newlands’ Law of Octaves – According to this ‘when elements are placed in order of increasing atomic masses, the physical and chemical properties of every 8th element are a repetition of the properties of the first element.’
Limitations of NewLands’ law of Octaves –
- Newland could arrange elements only up to calcium, out of the total 56 elements known.
- Same Elements were arranged in 2 slots which differed in property.
- Law of octaves was applicable only upto calcium (only for lighter elements)
- Mendeleev’s Periodic Table –Mendeleev believed that the atomic mass of an element was the most fundamental property in classifying elements. He arranged elements in the increasing order of their atomic masses and observed that the
elements showed repetition after certain intervals in their physical and chemical properties.
Merits of this arrangement –
- Vacant spaces were left for undiscoverd elements like eka-aluminium and eka- silicon.
- Left Space for Noble Gases
- Mendeleev’s periodic table was predicted properties of several undiscovered elements on the basis of their position in Mendeleev’s periodic table.
Demerits of this arrangement :-
- A correct position could not be assigned to hydrogen in the periodic table.
- Position of Isotopes was ambiguous.
- At certain places, an element of higher atomic mass was placed before an element of lower atomic mass.
- Modern Periodic Table – In 1913, Moseley, a student of Mendeleev, showed that the periodicity was a property of Atomic Number and not Mass Number.Modern periodic table is based on atomic number of elements.
Advantages of Modern Periodic Table –
- All elements are fundamentally arranged according to their atomic number. So it becomes easy to understand and compare their properties, thereby making it easier to remember the position of the elements
- The position of the elements in the periodic table makes it easy to predict and compare their properties, and explains the reason for their specific position in the periodic table
- It gives explanation for the periodicity of elements and tells the reason why all elements in a group having similar properties, which differ between the gropus and periods
- Positions of isotopes are taken care of within the element itself, unlike in Mendeleev periodic table.
- In the Modern periodic table, the metals, non-metals, transition metals, gases are separately placed in a specific location with a specific identity.