Periodic Classification of Elements – Notes
History of Periodic Table
Dobereiner’s law of triads: In a triad, the atomic mass of the middle element is equal to the arithmetic mean of the atomic masses of the other two.
Newlands law of octaves: When elements are arranged in increasing order of their atomic weights, the properties of the eighth element are a repetition of the properties of the first element.
Mendeleev’s law: The physical and chemical properties of elements are a periodic function of their atomic weights.
Modern Periodic Table
Atomic number is the number of protons in an atom.
The number of electrons in an atom is equal to the number of protons.
An atom is electrically neutral.