Chemistry class 12th Periodic_Table_Position

Position in the Periodic Table


The position of an element in the periodic table is determined by its atomic number (Z), electron
configuration, and chemical properties.
The periodic table consists of periods (horizontal rows) and groups (vertical columns).


1. Periods (Rows)
- There are 7 periods in the periodic table.
- The period number represents the number of electron shells (energy levels) in an atom.
- Example: Period 2 (Li, Be, B, C, N, O, F, Ne) all have 2 electron shells.


2. Groups (Columns)
- There are 18 groups, and elements in the same group have similar chemical properties.
- Example:
- Group 1: Alkali Metals (1 valence electron, very reactive)
- Group 17: Halogens (7 valence electrons, very reactive)
- Group 18: Noble Gases (8 valence electrons, very stable)


3. Blocks of the Periodic Table
- s-block: Groups 1 and 2 (alkali and alkaline earth metals)
- p-block: Groups 13-18 (non-metals, noble gases)
- d-block: Transition metals (Groups 3-12)
- f-block: Lanthanides and Actinides


4. Atomic Number and Electron Configuration
- The atomic number determines an element's position.
- Example: Sodium (Na, Z = 11) has an electron configuration of 1s2 2s2 2p6 3s1, placing it in
Period 3, Group 1.


5. Periodic Trends
- Atomic Radius: Decreases across a period, increases down a group.
- Ionization Energy: Increases across a period, decreases down a group.
- Electronegativity: Increases across a period, decreases down a group.