Samacheer Class 11 Chemistry - Alkali and Alkaline Earth Metals

NaOH + H 2 O ⇌ Na + + OH –
1. This reaction is an exothermic reaction. Sodium hydroxide is a strong base, completely dissociated in an aqueous medium. The heat evolved increases the stability. This phenomenon is strong enough to prove that sodium hydroxide crystals are readily dissolved in water.
2. NaCl is geologically stable. If kept dry, it will remain a free-flowing solid for years. Water can dissolve NaCl because the Na + ions are attracted by OH – in water and Cl – ions are attracted by H + in water. The solubility of NaCl does not increase the temperature. Based on this, NaOH is much more soluble due to its exothermic nature than sodium chloride.

* Efflorescence is a process of losing water of hydration from hydrate.
* Sodium carbonate crystallises as decahydrate which is white in colour.
* Upon heating, it loses the water of crystallization to form a monohydrate.
* Monohydrate (Na 2 CO 3.H 2 O) is formed as a result of efflorescence.
Na 2 CO 3.10H 2 O → Na 2 CO 3.H 2 O + 9H 2 O

2NH 3 + H 2 O + CO 2 → (NH 4 ) 2 CO 3
(NH 4 ) 2 CO 3 + H 2 O + CO 2 → 2NH 4 HCO 3
2NH 4 HCO 3 + NaCl → NH 4 Cl + NaHCO 3
2NaHCO 3 → Na 2 CO 3 + CO 2 + H 2 O

X forms X 2 SO 2. 10H 2 O. The metal is more likely to be sodium. So X is Na 2 SO 4. 10H 2 O. It is otherwise called as Glauber’s salt.

(i) 6Li(s) + N 2 (g) → 2Li 3 N(s)
(ii) 2NaHCO 3 (s) → Na 2 CO 3 (s) + CO 2 (g) + H 2 O(g)
(iii) Rb + O 2 → RbO 2
(iv) 2KOH + CO 2 → K 2 CO 3 + H 2 O
(v) CaCO 3 → CaO + CO 2
(vi) 2Ca + O 2 → 2 CaO

Diagonal relationship:
As observed in alkali metals, beryllium shows a diagonal relationship with aluminium. Similarities between beryllium and aluminium:
* Beryllium and aluminium have the same electronegativity values.
* Their changes per unit area are closed.
* BeCl 2 and AlCl 3 form a dimeric structure. Both are soluble in organic solvents and are strong Lewis acids.
* Be(OH) 2 and Al(OH) 3 dissolve in excess alkali to give beryllate ion [Be(OH) 4 ] 2- and aluminate ion [Al(OH) 4 ] –, respectively.
* Be and Al ions have a strong tendency to form complexes, e.g. BeF 4 2- and AlF 6 3-
* Both Be(OFI) 2 and Al(OH) 3 are amphoteric in nature.
* Carbide of Be – beryllium carbide (Be 2 C) and Al – aluminum carbide (Al 4 C 3 ) give methane on hydrolysis.
* Both beryllium and aluminium are rendered passive by nitric acid.

Lithium fluoride has high lattice enthalpy due to the small size of Li + and F –. So, due to the high lattice enthalpy, LiF is less soluble in water.

The largest use of Plaster of Paris is in the building industry as well as plasters. It is used for immobilizing the affected part of organ where there is a bone fracture or sprain. It is also employed in dentistry, in ornamental work and for making casts of statues and busts.

Beryllium ion (Be 2+ ) is smaller in size and it is involved in equal sharing of electrons with halogens to form a covalent bond, whereas magnesium ion (Mg 2+ ) is bigger and is involved in the transfer of electrons to form an ionic bond.

• Group 2 elements except beryllium are commonly known as alkaline earth metals because their oxides and hydroxides are alkaline in nature and these metal oxides are found in the Earth’s crust.
• Many alkaline earth metals are used in creating colours and used in fireworks.
• Their general electronic configuration is ns 2.
• Atomic and ionic radii of alkaline earth metals are smaller than alkali metals, on moving down the group, the radii increases.
• These elements exhibit a +2 oxidation state in their compounds.
• Alkaline earth metals have higher ionization enthalpy values than alkali metals and they are less electropositive than alkali metals.
• Hydration enthalpies of alkaline earth metals decrease as we go down the group.
• Electronegativity values of alkaline earth metals decrease down the group.
• Alkaline earth metal salts moistened with concentrated hydrochloric acid gave a characteristic coloured flame when heated on a platinum wire in a flame.

Diagonal relationship:
As observed in alkali metals, beryllium shows a diagonal relationship with aluminium. Similarities between beryllium and aluminium:
* Beryllium and aluminium have same electronegativity values.
* Their changes per unit area are closed.
* BeCl 2 and AlCl 3 form a dimeric structure. Both are soluble in organic solvents and are strong Lewis acids.
* Be(OH) 2 and Al(OH) 3 dissolve in excess alkali to give beryllate ion [Be(OH) 4 ] 2- and aluminate ion [Al(OH) 4 ] –, respectively.
* Be and Al ions have strong tendency to form complexes, e.g. BeF 4 2- and AlF 6 3-
* Both Be(OFI) 2 and Al(OH) 3 are amphoteric in nature.
* Carbide of Be – beryllium carbide (Be 2 C) and Al – aluminium carbide (Al 4 C 3 ) give methane on hydrolysis.
* Both beryllium and aluminium are rendered passive by nitric acid.

The strength of metallic bond in alkaline earth metals is higher than the alkali metals due to the presence of 2 electrons in its outermost shell as compared to alkali metal which has only 1 electron in the valence shell. Therefore alkaline earth metals are harder than alkali metals.

It is a hemihydrate of calcium sulphate. It is obtained when gypsum,
CaSO 4.2H 2 O is heated to 393 K.
2CaSO 4.2H 2 O(s) → 2CaSO 4.H 2 O + 3H 2 O
Above 393 K, no water of crystallisation is left and anhydrous calcium sulphate, CaSO 4 is formed. This is known as ‘dead burnt plaster’.

• The Alabaster variety of gypsum was used by the sculptors.
• Gypsum is used in making dry walls or plasterboards.
• Gypsum is used in the production of Plaster of Paris, which is used as a sculpting material
• Gypsum is used in making surgical and orthopedic casts.
• It plays an important role in agriculture as a soil additive, conditioner and fertilizer
• Gypsum is used in toothpaste, shampoo and hair products.
• Calcium sulphate acts as a coagulator in making tofu.
• It is also used in baking as a dough conditioner.
• Gypsum is a component of Portland cement, where it acts as a hardening retarder to control the speed at which concrete sets.
• Gypsum is used to give colour to cosmetics and drugs.
• Gypsum plays a very important role in winemaking.

Magnesium:
* A typical adult human body contains about 25 g of magnesium and 1200 g of calcium.
* Magnesium plays an important role in many biochemical reactions catalyzed by enzymes.
* It is the co-factor of all enzymes that utilize ATP in phosphate transfer and energy release.
* It also essential for DNA synthesis and is responsible for the stability and proper functioning of DNA.
* It is also used for balancing electrolytes in our body.
* Deficiency of magnesium results in convulsion and neuromuscular irritation.
* The main pigment that is responsible for photosynthesis, chlorophyll, contains magnesium which plays an important role in photosynthesis.
Calcium:
* Calcium is a major component of bones and teeth.
* It is also present in blood and its concentration is maintained by hormones (calcitonin and parathyroid hormone).
* The deficiency of calcium in the blood causes it to take a longer time to clot. It is also important for muscle contraction.

• Magnesium oxide has very strong ionic bonds as compared to magnesium fluoride.
• Mg 2+ and O 2- have charges of +2 and -2, respectively.
• Oxygen ion is smaller than fluoride ion.
• The smaller the ionic radii, the smaller the bond length in MgO and the bond is stronger than MgF 2.
• Due to more strong bond nature in MgO, it has a high melting point than MgF 2.