S-Block & P-Block Elements

The periodic table is organized into blocks based on which subshell is being filled. The s-block (Groups 1 and 2) and p-block (Groups 13-18) together make up the representative elements. Understanding their properties and trends is fundamental to inorganic chemistry.

S-Block Elements

S-block elements have their outermost electrons in the s-orbital. They include:

Group 1 -- Alkali Metals: Li, Na, K, Rb, Cs, Fr

• Highly reactive metals with one valence electron
• Soft, low melting points, low density
• React vigorously with water: 2Na + 2H₂O --> 2NaOH + H₂
• Reactivity increases down the group (Cs is more reactive than Li)
• Flame colours: Li (red), Na (yellow), K (violet)

Group 2 -- Alkaline Earth Metals: Be, Mg, Ca, Sr, Ba, Ra

• Two valence electrons, less reactive than Group 1
• Higher melting points and harder than alkali metals
• React with water (Ca onwards): Ca + 2H₂O --> Ca(OH)₂ + H₂

Key Trends in S-Block

| Property | Down the group | |----------|---------------| | Atomic radius | Increases | | Ionization energy | Decreases | | Electronegativity | Decreases | | Reactivity | Increases | | Metallic character | Increases |

P-Block Elements

P-block elements (Groups 13-18) show much more diversity. They include metals, metalloids, and non-metals.

Group 13 (Boron family): B is a metalloid; Al is the most abundant metal in Earth's crust.

Group 14 (Carbon family): C is the basis of organic chemistry; Si is used in semiconductors.

Group 15 (Nitrogen family): N₂ makes up 78% of air; P is essential for life (DNA, ATP).

Group 16 (Oxygen family/Chalcogens): O₂ is essential for respiration; S is used in H₂SO₄ production.

Group 17 (Halogens): F, Cl, Br, I -- very reactive non-metals. Form salts with metals.

Group 18 (Noble gases): He, Ne, Ar, Kr, Xe, Rn -- very stable, low reactivity.

Important Compounds

• NaOH (caustic soda): Used in soap making, widely used in Nepal's small-scale industries
• Na₂CO₃ (washing soda): Water softening, glass making
• CaO (quicklime): Construction (plaster, cement)
• NaHCO₃ (baking soda): Cooking, antacid

Nepal Connection

Nepal's cement industry uses calcium compounds (CaO, CaCO₃) extensively. Sodium hydroxide (NaOH) is used in traditional soap-making practices in rural Nepal.

Key Takeaways

• S-block: Groups 1 and 2 are highly reactive metals
• Reactivity of metals increases down the group
• P-block contains metals, metalloids, and non-metals
• Noble gases have complete octets and are mostly unreactive