Chapter Summary
When 3 elements are arranged in order of increasing atomic masses, the atomic mass of the middle element is equal to arithmetic mean of remaining 2 elements.
Example: Lithium (7), Sodium (23) and Potassium (39)
Every eighth element has similar physical and chemical properties when they are arranged in increasing order of their relative masses.
Newlands' Octaves could be valid upto calcium only.
Properties of elements are the periodic function of their relative atomic masses.
Mendeleev left some blank spaces in his periodic table in order to place the elements having similar properties in the same group.
Properties of elements are the periodic function of their atomic numbers.
There are 18 groups and 7 periods in the modern periodic table.
Number of valence electron remains the same while moving from top to bottom in a group.
Number of valence electron increases while moving from left to right in a period.
Valency remains the same on moving from top to bottom in a group.
Valency first increases upto 4 on moving from left to right in a group and then decreases upto zero.
Atomic size increases on moving from top to bottom in a group and decreases on moving from left to right in a period.
Atomic radius increases on moving from top to bottom in a group and decreases on moving from left to right in a period.
Metallic character decreases on moving from left to right in a period.
Metals are on LHS of periodic table.
Tendency to lose electrons decreases on moving from left to right in a period.
Tendency to lose electrons increases on moving from top to bottom in a group.
Tendency to gain electrons increases on moving from left to right in a period.