NCERT Solutions for Class 10th Science
Chapter 5. Periodic Classification of Elements
- Groups having three elements each. So he called these groups called triads.
- According to Dobereiner's Traids "The order of increasing atomic masses; the atomic mass of the middle element was roughly the average of the atomic masses of the other two elements".
- According to Newlands’ Law of Octaves "Every eighth element repeat the properties of the first element".
- Newlands’ Law of Octaves worked well with lighter elements only.
- When Mendeleev started work on Periodic Table, oniy 63 elements were known.
- The Modern Periodic Table has 18 vertical columns known as ‘groups’
and 7 horizontal rows known as ‘periods’.
- The Modern Periodic Law state that ‘Properties of elements are a periodic function of their atomic number.’
- The valency of an element is determined by the number of valence electrons present in the outermost shell of its atom.
- The atomic size may be visualised as the distance between the centre of the nucleus and the outermost shell of an isolated atom.
- The atomic radius decreases in moving from left to right along a period. This is due to an increase in nuclear charge which tends to pull the electrons closer to the nucleus and reduces the size of the atom.
- Boron, silicon, germanium, arsenic, antimony, tellurium and polonium are intermediate in properties and are called metalloids or semi metals.