10th Class: s-Block Elements

s-Block Elements

• s-Block elements are the metals in Group IA and Group IIA of the periodic table.
• They are called s-Block elements because s-orbitals are being filled in their outermost shells.

Alkali Metals

• Alkali metals are the elements in Group IA of the periodic table, except hydrogen.
• They are called "Alkali metals" because they produce alkaline solutions with water.
• Alkali metals include lithium, sodium, potassium, rubidium, caesium, and francium.
• They are very reactive metals and produce strong alkaline solutions with water.

Electronic Configurations of Alkali Metals

• Alkali metals have only one electron in the 's' orbital of their valence shell.
• They lose their one electron in the valence shell to form monopositive ions (M+).
• They form ionic compounds and show +1 oxidation state.
• Electronic configurations and physical constants of alkali metals are given in Table 2.1.

Occurrence of Alkali Metals

• Alkali metals occur in nature in the combined state.
• Sodium and potassium are abundant alkali metals and each constitute about 2.4% of the earth's crust.
• Common minerals of alkali metals are given in Table 2.3.

Peculiar Behaviour of Lithium

• Lithium is quite different from the other alkali metals in many of its properties.
• Deviation shown by lithium can be explained on the basis of its small radius and high charge density.
• Anomalous properties of lithium are due to the fact that lithium is unexpectedly far less electropositive than sodium.
• Differences of lithium from other alkali metals are listed in 12 points.

General Behaviour of Alkali Metals

• The reducing property of an element depends on the magnitude of its ionization energy.
• Reducing agent is a substance that can lose electrons.
• Alkali metals are strong reducing agents and react readily with halogens giving alkali metal halides.

Trends in Chemical Properties of Alkali Metals

• Low ionization energies make the alkali metals, the most reactive family of metals.
• Very high second ionization energies indicate that oxidation number higher than 1, are ruled out for the alkali metals.
• The cations of alkali metals have low charge and large radii than the radius of any cation from the same period, so the lattice energies of their salts are relatively low.

Alkaline-Earth Metals

• Alkaline-earth metals are the elements in Group IIA of the periodic table.
• They are called "Alkaline-earth metals" because they produce alkaline solutions with water.
• Alkaline-earth metals include beryllium, magnesium, calcium, strontium, barium, and radium.

Electronic Configurations of Alkaline-Earth Metals

• Alkaline-earth metals have two electrons in the 's' orbital of their valence shell.
• They lose their two electrons in the valence shell to form dipositive ions (M2+).
• They form ionic compounds and show +2 oxidation state.
• Electronic configurations and physical constants of alkaline-earth metals are given in Table 2.2.

Occurrence of Alkaline-Earth Metals

• Alkaline-earth metals occur in nature in the combined state.
• Magnesium and calcium are very abundant in the earth's crust.
• Common minerals of alkaline-earth metals are given in Table 2.4.

Peculiar Behaviour of Beryllium

• Beryllium is the lightest member of the series and differs from the other group IIA elements in many ways.
• Main points of difference are:
  • Beryllium metal is almost as hard as iron and hard enough to scratch glass.
  • The melting and boiling points of beryllium are higher than other alkaline earth metals.
  • As reducing agents, the group IIA metals are all powerful enough to reduce water, at least in principle.
  • Beryllium in particular is quite resistant towards complete oxidation, even by acids, because of its BeO coating.### s-Block Elements

Properties of Alkali Metals

• React with water to form hydroxides and hydrogen gas
• React with nitrogen to form nitrides
• React with carbon to form carbides
• React with halogens to form halides

Trends in Chemical Properties of Alkaline-Earth Metals

• Burn in oxygen to form oxides or peroxides
• React with nitrogen to form nitrides
• React with hydrogen to form hydrides
• React with sulphur to form sulphides
• React with halogens to form halides

General Trends in Properties of Compounds of Alkali and Alkaline Earth Metals

• Oxides: dissolve in water to give strong alkaline solutions
• Hydroxides: soluble in water, strong bases, and hygroscopic
• Carbonates: soluble in water, stable towards heat, except Li2CO3
• Nitrates: soluble in water, decompose on heating to give O2, NO2, and metal oxide
• Sulphates: soluble in water, except BeSO4 and MgSO4, which are insoluble

Commercial Preparation of Sodium by Down's Cell

• Electrolysis of fused sodium chloride at 600°C
• Produces sodium metal and chlorine gas
• Advantages: no metallic fog, easy collection of sodium, and no attack on cell material

Commercial Preparation of Sodium Hydroxide by the Diaphragm Cell

• Electrolysis of aqueous sodium chloride solution
• Produces chlorine gas at anode and sodium hydroxide solution at cathode
• Sodium hydroxide solution can be evaporated to produce 50% NaOH and 1% NaCl

Role of Gypsum in Agriculture and Industry

• Gypsum is a source of calcium and sulphur for plants
• Sulphur is essential for plant growth and development
• Gypsum is used as a fertilizer to improve soil quality
• Plaster of Paris, a product of heated gypsum, is used in construction, medicine, and industry### Hard Finish Plasters
• Made by calcinating anhydrous sulphate with alum or borax
• Set very slowly, giving a hard finish
• Can be mixed with wood pulp to form a material used in construction of buildings as wall boards and partitions

Portland Cement

• Made by strongly heating a finely powdered mixture of clay and limestone
• Final product, known as clinker, is cooled and then ground into a fine powder
• Gypsum is added during grinding to prevent cement from hardening too rapidly, increasing the setting time

Role of Lime in Agriculture and Industry

Agriculture

• Used to neutralize acidic soils, increasing the amount of readily soluble phosphorus
• Used to make lime-sulphur sprays, which have a strong fungicidal action
• Calcium oxide is essential for normal plant development, stimulating root hair growth and normal leaf development

Industry

• Used in extraction and refining of metals
• Used in paper, cement, and leather industries
• Used in glass manufacture, reacting with sand at high temperature to form calcium silicate
• Used in ceramic industry for producing sanitary materials
• Used in refining sugar and other food products
• Used in manufacturing of bleaching powder, which is used for bleaching fabric and paper pulp
• Used as a dehydrating agent, for example, in preparation of absolute alcohol and drying of ammonia gas

Functions of Calcium in Plant Growth

• Essential for normal development of plants
• Stimulates development of root hairs and entire root system
• Necessary for normal leaf development and tends to accumulate in leaves and bark
• Essential for optimum activity of microorganisms that produce nitrates

Key Points

• Alkali metals have only one electron in their valence shell, losing one electron to form monovalent positive ions
• Alkaline earth metals have two electrons in their valence shell, losing two electrons to form dipositive ions
• Lithium behaves differently from other alkali metals, forming only normal oxide and reacting with nitrogen to form lithium nitride
• Beryllium is the only member of group II that reacts with alkalies to give hydrogen