Summary of S-Block 01 | S-Block | CLASS 11 | JEE | NEET | PACE SERIES

Summary of the Video: "S-Block 01 | S-Block | CLASS 11 | JEE | NEET | PACE SERIES"

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Main Ideas and Concepts Covered:

1. Introduction to S-Block Elements:
   • S-Block Elements are those whose last electron enters the s-orbital.
   • These include Group 1 (Alkali Metals) and Group 2 (alkaline earth metals).
   • Hydrogen and helium are exceptions: hydrogen is covered separately, helium’s properties align more with Group 18 (noble gases) and will be discussed later.
   • Radioactive elements like radium are mentioned but not the focus here.
2. Electronic Configuration and Position in Periodic Table:
   • Group 1 elements have electronic configuration ending in ns¹.
   • Group 2 elements have configuration ending in ns².
   • The principal quantum number corresponds to the period number.
   • Atomic number and electron configuration help identify group membership.
3. Group 1 Elements (Alkali Metals):
   • Highly reactive metals that form strong bases (alkalis) when reacting with water.
   • Examples include Lithium, Sodium, Potassium, Rubidium, Cesium.
   • Reaction with water produces hydroxides (strong bases) and hydrogen gas.
   • Alkali Metals are soft, silvery-white (except Cesium which is pale gold).
   • Reactivity and softness increase down the group (Li < Na < K < Rb < Cs).
   • Atomic radius and atomic volume increase down the group.
   • Oxidation state is +1 for Alkali Metals in compounds.
4. Periodic Trends in S-Block Elements:
   • Atomic Radius: Increases down the group due to addition of shells.
   • Atomic Volume: Increases down the group.
   • Density: Generally decreases down the group due to increasing volume; Lithium floats on kerosene because its density is less than kerosene.
   • Melting and Boiling Points: Decrease down the group due to weakening metallic bonds.
   • Electropositive Character: Increases down the group because electrons are more easily lost as atomic size increases.
   • Ionization Energy: Decreases down the group due to weaker attraction between nucleus and valence electron.
5. Hydration and Ionic Mobility:
   • Smaller ions with higher charge attract more water molecules (higher hydration).
   • Hydration affects ionic radius and ionic mobility in aqueous solutions.
   • Lithium ion has the highest hydration, Cesium the lowest.
   • Ionic mobility is inversely related to hydration: more hydrated ions move slower.
   • Sequence of ionic mobility in water: Cs⁺ > Rb⁺ > K⁺ > Na⁺ > Li⁺.
6. Oxidation States and Electron Removal:
   • Alkali Metals typically show +1 oxidation state.
   • Removal of electrons from inner shells requires much more energy, so only outermost electrons are lost.
   • Energy needed to remove electrons decreases down the group as atomic size increases.
7. Physical Properties:
   • Colors: Mostly silvery-white except Cesium (pale gold).
   • Softness increases down the group.
   • Density trends explained by atomic volume and mass.
   • Alkali Metals stored under kerosene or paraffin to prevent reaction with air/moisture.
8. Crystal Structure:
   • Alkali Metals crystallize in body-centered cubic (bcc) structure.
   • Coordination number in bcc structure is 8.
   • Detailed crystal structure studies are covered in higher classes.
9. Flame Test and Colors:
   • Alkali Metals produce characteristic flame colors used for identification:
     • Lithium: Crimson red
     • Sodium: Golden yellow
     • Potassium: Lilac/violet
     • Rubidium and Cesium have distinct flame colors (not detailed here).
   • Mnemonics suggested for remembering flame colors.
10. Exam Tips and Revision Advice:
    • Emphasis on making good notes and revising repeatedly.
    • Understanding periodic trends and properties helps solve exam questions.
    • Expect direct questions on trends like atomic size, ionization energy, flame tests, and reactivity.

Detailed Bullet Points of Methodology/Instructions:

• To determine if an element is an s-block element:
  • Check if the last electron enters the s-orbital (ns¹ or ns²).
  • Confirm group number (1 or 2) and period number (principal quantum number).
• To predict properties of Alkali Metals:
  • Use periodic trends: atomic radius, ionization energy, electropositive character.
  • Expect reactivity and softness to increase down the group.
  • Expect density to decrease generally due to volume increase.
  • Know the typical +1 oxidation state.
• To understand hydration and ionic mobility:
  • Smaller ions with higher ...

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