This document provides information on alkaline earth metals and alkali metals. It discusses their isolation methods, physical properties, reactivity, oxides, carbonates, and other salts. It also covers diagonal relationships between elements, hydrides, solvation of alkali metal ions, alkyls and aryls, complexation behavior, and biological importance of alkali metals. Specifically, it notes that alkaline earth metals like calcium, barium and strontium are isolated through electrolysis of their stable salts, while beryllium and magnesium are obtained through electrolysis of their chlorides. It also discusses how lithium shows stronger tendencies toward covalency than other alkali metals in forming covalent alkyls and aryls.

1. Block Elements
Course: B.Sc.
Microbiology/Biotechnology/Biochemistry
Sem II
Sub: Inorganic Chemistry
Unit 4.2

3. Comparison study of alkaline earth metals with alkali metals:
1. Ca, Ba & Sr : isolated – stable salts : electrolytic method =
same alkali metals.
Be & Mg – electrolysis of their chlorides.
2. Metals : soft with silvery luster & very light.
3. React with water & oxygen,
much activity towards other substances.
4. Mg & Be : harder & more stable,
absorbing N , Mg = Li.

4. Higher density & high B.P. & M.P.
5. Electropositive nature : increase with Be to Radium & Li to
Caesium.
6. Oxides of alkaline earth metals : less affinity – water ,
compared to alkali metals.
Alkaline & alkali hydroxide : good absorbents for CO2 –
carbonates.
7. Difference betn alkali & alkaline carbonates.
with exception of Li carbonates, other alkali carbonates –
dissolves in water & mild alkali solutions.
carbonates of Mg, Ca, Sr, Ba – sparingly sol. & ppts.

5. 8. Alkali sulphates & phosphates : soluble ,
Ca, Sr, Ba – less soluble.
9. chlorides, acetates, nitrates, cyanides – similar.
salts – not imp. & used.

6. Diagnol relationship
• first element of a group = similar properties with the
second element of the next group : diagonal
relationship.
• Reason – In the periodic table,
• from left to right - atomic and ionic size decreases and
polarizing power increases.
• from top to bottom - atomic and ionic size increases
and polarizing power decreases.
• consider these properties, the elements which are
present diagonally - similar properties.
• This is called as diagonal relationship.

7. Diagonal Relationship between Beryllium and
Aluminium
• The ionic radius of Be2+ - 31 pm;
• charge/radius ratio - same as that of the Al3+ ion.
• Hence beryllium resembles aluminium in some ways.
• Some of the similarities are:
• (i) Like aluminium, beryllium - not attacked by acids because -
presence of an oxide film on the surface of the metal.
• (ii) Beryllium hydroxide dissolves in excess of alkali - beryllate
ion, [Be(OH)4]2- .

8. • aluminium hydroxide - aluminate ion, [Al(OH)4]-.
• (iii) The chlorides of both beryllium and aluminium have
Cl- bridged chloride structure in vapour phase.
• Both the chlorides are soluble - organic solvents and
strong Lewis acids. They are used as Friedel Craft
catalysts.
• (iv) Beryllium and aluminium ions - strong tendency to
form complexes, BeF4
2-, AlF6
3-.

9. Hydrides
• Hydrogen forms compds with – metals & nonmetals : hydride.
• All compds of Hydrogen – hydrides but not all H-containing
compds – hydridic character.
• Hydridic substances – act as H- ion donors.
• Distinguish hydridic subatances(NaH) from : neutral (CH4) or
acidic (HCl).
Classification of Hydrides:
1. Ionic , 2. Covalent, 3. Interstitial, 4. polymeric.

10. Reaction of Hydrides
• React with water & form metal hydroxide & H2 : strong basic
property of hydride ion.
• H- + H2O H2 + OH
• good reducing agent.
• Used to prepare complex hydrides.
• E.g., LiAlH4, NaBH4.

11. Solvation of Alkali metal ions:
• Solvent molecules : surround a metal ion in solution -
solvation.
• if, solvent is water : hydration.
• Alkali metal ions : hydrated.
• Small ion – high charge density & attract solvent : strongly –
hydration.
• Energy evolved : hydration energy.
• Li+ - smallest , hydration – highest hydration energy.
• extent of hydration decreases : down the group.
• Hydration - affects ionic mobility.
• Li - smallest ion : highly mobile, but in fact the reverse is
time.
• because the hydrated radius of Li+ : largest , least mobile
and least conducting in solution.
• salts of alkali metals -soluble in water

12. • Alkyls and Aryls
• Lithium : stronger tendency to covalency than the other alkali
metals.
• forms covalent alkyls and aryls.
• compounds : tetrameric or hexameric and
• made - by reaction of lithium with the alkyl / aryl halide.
• R Cl + Li Li R + LiCl

13. • methyl derivative - tetrameric [(LiCH3)4], covalent and soluble
in organic solvents.
• four Li atoms : occupy the corners of a tetrahedron with the
methyl groups.
• These compounds - starting materials for synthesis of organo
metallic and organic compounds.
• alkyls of Na, K, Rb and Cs : ionic.

14. Complexation Behaviour of Alkali Metals
• alkali metals - weak complexing ability.
Reason : factors that favour complexation viz, small size, high
nuclear charge and availability of empty orbitals of low energy
are lacking in alkali metals.
• Aqua complexes like [Li(H2O)4]+, [Cs(H2O)6]+ : known.
• number of chelates are known.
• important development in the field of alkali metal chemistry :
discovery of complexes with cyclic ethers and cryptands
(cryptates) i.e. with macro cyclic molecules containing
nitrogen and oxygen.

15. • cyclic ethers are called crown ethers; they have varying sizes
of rings and form complexes with alkali metal ions by donating
electron density through the oxygen atoms.
A – crown ether b- cryptands

16. • cryptates -more selective and stronger complexing agents
than the crown ethers, with eight donor atoms (nitrogen and
oxygen) surrounding the metal ion completely.
• ability of crown ether or a cryptands : trap a metal ion
depends on the size of both the cavity and the metal ion.

17. Biological importance
• Living organisms - 15 metals for different biological
processes.
• biologically active.
• Sodium and potassium ions - charge carriers and
• balancing the electrical charges - negatively charged
macromolecules in the cell.
• Na+ - major cation in the extra cellular fluid and
• concentration - 0.15 M,
• actively expelled from the cell where its concentration is
about 0.01 M .
• K+ - major cation inside the cell (0.15 M)
• whereas its concentration in the extra cellular fluid - 0.03
M.

18. - uneven concentration of Na+ and K+ on either side of
the cell wall - controlled by the sodium-potassium
pump .
- large amount of energy is needed to maintain.
- energy : provided by hydrolysis of ATP.
- Na+ and K+ - maintaining the osmotic pressure inside
the cell.
- different ratio of Na+ to K+ inside and outside the cell :
characteristic electrical potential across the cell
membrane and muscle cells.
- activate specific enzymes.
- Lithium salts : used as anti-depressants.

19. References
• Advanced Inorganic Chemistry by Volume I, Satyaprakash, G D Tuli,
S. K. Basu, R. D. Madan
• Modern Inorganic Chemistry’ G. F. Liporni, ELBS, 4th edition, Collins
educational, 1983