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alkali metals

alkaline earth metals

CBSE Class 11 Chemistry Chapter 10 Revision Notes

S-block elements are those found in Groups 1 and 2 of the current periodic table. There are two sorts of s block elements: those with one electron (s1) and those with two electrons (s2) in their s-subshell. Hydrogen (H), lithium (Li), helium (He), sodium (Na), beryllium (Be), potassium (K), magnesium (Mg), rubidium (Rb), calcium (Ca), cesium (Cs), strontium (Sr), francium (Fr), barium (Ba), and radium (Ra) make up the S-block.

Chapter 10: S- block Elements Revision Notes

  • Because the s-orbital can only hold two electrons, the s-block is divided into two groups.
  • The electrical configuration of s-block components is either nsl or 2 in general.

Alkali Metals[Group-I]

  • The valence shell of Group-I elements has one electron. They don't exist in the natural or unrestricted condition.
  • Because their oxides and hydroxides generate powerful alkalies like NaOH and KOH, these elements are collectively known as alkali metals. Lithium is referred to as a bridging element.

Alkali Metals and Their Applications

Uses of Lithium

(i) In the purification of copper and nickel, lithium is utilised as a deoxidizer.

(ii) Both main and secondary batteries are made of lithium.

(iii) For meteorological applications, lithium hydride is employed as a hydrogen source.

(iv) Lithium aluminium hydride (LiAlH4) is an effective reducer.

(v) Glass is made from lithium carbonate.

Uses of Sodium

(i) In the laboratory, it's used as sodium amalgum (synthesis of organic compounds).

(ii) In a sodium vapour lamp, sodium is utilised.

(iii) It is employed in nuclear reactors in a molten condition.

(iv) In high-temperature thermometers, a sodium-potassium alloy is used.

Uses of Potassium

(i) Potassium salts are used in fertilisers.

(ii) A reducing agent is used.

Uses of Cesium

(i) As a propellant for rockets

(ii) In photographic cells

Alkaline Earth Metals

  • They were given this name because they were alkaline in nature, similar to alkali metal oxides, and they were discovered in the earth's crust.
  • Be (Beryllium), Ca, Mg, Sr, and other elements are examples.

Electronic Configuration

  • The [noble gas] ns2 represents their basic electrical configuration.

Atomic and Ionic Radii

  • Alkaline earth metals have a lower atomic and ionic radius than alkali metals. The atomic and ionic radii within the group grow as the atomic number rises.

  • The reason for this is because these elements only contain two valence electrons, and the nucleus-valence electron force of attraction is extremely modest.

Ionization Enthalpies

  • Due to the relatively high size of the atoms, these metals have low ionisation enthalpies. The group ionisation enthalpies are projected to decrease as atomic sizes decrease.
  • Alkaline earth metals have greater first ionisation enthalpies than alkali metals due to their smaller size in compared to alkali metals.

Physical Characteristics

(i) They are more resistant to corrosion than alkali metals.

(ii) Due to their tiny size, M.P and B.P are greater than the comparable alkali metals.

(iii) As the group progresses, the electropositive character becomes more prominent.

(iv) With the exception of Be and Mg, all of these metals give the flame a distinct colour.

(v) The thermal and electrical conductivity of alkaline earth metals is excellent.

Chemical Properties

1. Oxidation reaction. Because a thin coating of oxide forms on their surface, beryllium and magnesium are kinetically inert to oxygen.

As you progress through the group, your reactivity to oxygen grows.

2. The water reaction. These metals are less reactive to water than alkali metals because they are less electropositive.

Magnesium interacts with steam or boiling water. Even with cold water, the rest of the members respond.

3. Halogen-halogen reaction At the right temperature, they react with the halogens to generate the MX2 halides.

M + X2 ——–> MX2 (X = F, Cl, Br, I)

The thermal breakdown of (NH4)2 BeF4 is utilised to make BeF2.

4. Hydrogen reactivity. These metals, with the exception of Be, react immediately with hydrogen to generate metal hydrides when heated.

Alkaline Earth Metal Compounds: General Characteristics

Hydroxides and Oxides

(i) When alkaline earth metals come into contact with oxygen, they create MO (monoxide).

(ii) These oxides are extremely heat stable.

(iii) BeO is amphoteric, whereas other elements' oxides are ionic.

(iv) With the exception of They are basic in nature, and when they come into contact with water, they create sparingly soluble hydroxides.

MO + H2O ———-> M(OH)2

(v) Alkaline earth metal hydroxides are less stable and basic than alkali metal hydroxides.

(vi) Beryllium hydroxide is naturally amphoteric.

Halides

  • At appropriate temperatures, alkaline earth metals combine directly with halogens to form halides, MX2.
  • They can also be made by reacting metals, metal oxides, and metal hydroxides with halogen acids (HX).

Sulphates

(i) Alkaline earth metal sulphates are white solids that are heat stable.

(ii) BeS04 and MgS04 are both water soluble. From BeS04 to BaS04, the solubility drops.

Reason. Be2+ ions and Mg2+ ions surpass the lattice enthalpy factor because to their higher hydration enthalpies. Their sulphates are water soluble.

Carbonates

Alkaline earth metal carbonates are thermally unstable and breakdown when heated.

Calcium's Most Important Compounds

Limestone or Calcium Carbonate (CaC03)

Calcium carbonate is found in nature in a variety of forms, including limestone, marble, and chalk. It may be made by passing a little quantity of CO2 through slaked lime.

Ca(OH)2 + C02 ———> H20 + CaC03

It can also be made by reacting a sodium carbonate solution with calcium chloride.

CaCl2 + Na2C03 ————> 2NaCl + CaC03

(i) It's used in the production of Quick Lime.

(ii) When MgC03 is utilised as a flux in metal extraction.

(iii) It's an anti-acid.

(iv) In the production of high-grade paper.

Sulfate of calcium (Plaster of Paris)

Preparation: It is obtained when gypsum CaS04– 2 H20 is heated to 393 K \s2(CaS04-2H20)

Anhydrous CaS04, sometimes known as 'dead burned plaster,' is generated above 393 K.

(i) It is a white atmosphous powder with the following properties:

(ii) Within 15 minutes of being combined with enough water, it forms a plastic hard mass.

Uses:

(i) Commonly employed in the production of pottery, ceramics, and other similar items.

(ii) Used to fix a broken bone or sprain in surgical dressings.

(iii) For the creation of sculptures, ornamental work, and decorative materials, among other things.

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