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9th Class notes of chemistry chapter 3

In nineteenth century attempts were made to arrange elements in a systematic manner.

Dobereiner arranged elements in a group of three called triads.

Newlands arranged elements in groups of eight like musical notes.

Mendeleev constructed Periodic Table containing periods and columns, by arranging elements in order of increasing atomic weights.

There are total eighteen groups and seven periods in the modern Periodic Table.

Depending on outermost electrons and electronic configuration, element in periodic table are grouped in s, p, d and f blocks.

Atomic size increases down a group but decreases along the period .

Ionization energy decreases down a group but increases along a period.

Shielding effect is greater in atoms with greater number of electrons.

Electronegativity increases along a period and decreases down the group.

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