 |
Introduction |
| |
At the turn of the nineteenth century, about 30 elements were known. 50 years later by the 1850s, scientists had discovered sixty three chemical elements and the numbers kept increasing. |
|
Dobereiner's Triads |
| |
In the famous atomic theory of John Dalton (1805), it was suggested that the atoms of an element have a characteristic mass. So, attempts were made to classify elements on the basis of their atomic masses. |
|
Newlands' Law of Octaves |
| |
Newland arranged many of the known elements in the increasing order of their atomic masses. |
|
Mendeleev's Periodic Table |
| |
Mendeleev classified the then known 56 elements on the basis of their physical and chemical properties in the increasing order of the atomic masses, in the form of a table. |
|
The Modern Periodic Table |
| |
The modern periodic table is also known as the long form of the periodic table or the extended form of the periodic table. |
|
Cause of Periodicity of Elements |
| |
Members of the same group have similar electronic configuration of the valence shell and thus show same valency. |
|
Position of Elements in the Modern Periodic Table |
| |
The number of elements in these periods is based on the way electrons are filled into various shells. |
|
Trends in the Modern Periodic Table |
| |
The distance from the centre of the nucleus to the outermost shell of an atom is called the atomic radius of that atom. |
|
Relation Between Atomic Number and Atomic Mass |
| |
While studying the periodic table, it will be noticed that with the increase in the atomic number, there is an increase in atomic mass as well (with some exceptions). |
|
Summary |
| |
The earliest classification was into metals and non-metals, which was on the basis of physical and chemical properties. |
|
Question and Answers |
| |
|
|
Multiple Choice Questions |
| |
|
