The s- Block Element short cut notes revised in 1 hour
Chapter 10
The s- Block Element
Important points
* Groups (1 & 2) belong to the s-block of the Periodic Table.
*Group 1 consists of : lithium, sodium, potassium, rubidium, caesium and
francium and collectively known as the alkali metals.
*Group 2 include : beryllium, magnesium,calcium, strontium, barium and
radium. Except Beryllium they are known as alkaline
Physical properties-
a) Large atomic radii: The atomic radii of alkali metals are the largest in their
respective periods. These increase as we travel down the group.
b) Large ionic radii: The ionic radii increase as we move down the group due to the
addition of a new energy shell with each succeeding element.
c) Low ionization enthalpy: The ionization enthalpies decrease as we move down
the group.The ionization enthalpies of the alkali metals are the lowest due to
loosely held s- electron.
d) Hydration enthalpy: It decreases with the increase in ionic radii.The hydration
enthalpy of Li ion is the maximum and the hydration enthalpy of Cs ion is the
minimum.
e) Oxidation state: The alkali metals exhibit oxidation state of +1 in their
compounds and are strongly electropositive in character. The electropositive
character increases from Li to Cs.
f) Metallic character: The metallic character increases down the group.
g) Melting point and boiling point:: The m p and b p of alkali metals are very low
and decrease with increase in atomic number.
h) Nature of bonds formed: These metals form ionic bonds. The ionic character
increases as we down the group.
i) Flame colouration: All the alkali metals impart a charactersistic colour to the
flame.
j) Photoelectric effect: Alkali metals (except Li) exhibits photoelectric effect.
Chemical features of alkali metals:
a) Reducing character: As the ionization enthalpies of the alkali metals decrease
down the group their reducing character or reactivity in the gaseous state
increases down the group. i.e., Li < Na < K < Rb < Cs .
b) Reaction with dihydrogen: Alkali metals react with dry hydrogen at about
673 K to form crystalline hydrides which are ionic in nature and have high
melting points.
Heat
2 M + H2 2M + H-
c) Oxides and hydroxides: Alkali metals when burnt in air form different
compounds, for example the alkali metals on reaction with limited quantity of
oxygen form normal oxides ( M2O) M= Li, Na, K, Rb, Cs
d) Reaction with halogens: The members of the family combine with halogen
to form corresponding halides which are ionic crystalline solids.
Reactivity of alkali metls with particular halogen increases from Li to Cs.
e) Reaction with water: Alkali metals react with water and other compounds
containing acidic hydrogen atoms such as hydrogen halides, acetylene etc. to
liberate hydrogen gas.
f) Solubility in liquid ammonia: All alkali metals dissolve in liquid ammonia
giving deep blue solutions which are conducting in nature.
g) Reaction with sulphur and phosphorus: Alkali metals react with sulphur and
phosphorus on heating to form sulphides and phosphides respectively.
Diagonal relationship between Li and Al
Li resembles Mg mainly due to similarity in sizes of their atoms and ions. The main
points of similarity are:
i) Both are quite hard.
ii) Both LiOH and Mg(OH)2 are weak bases.
iii) Carbonates of both on heating decompose to produce oxides and
carbondioxide.
iv) Both react with nitrogen to give ionic nitrides.
v) Nitrates of both decompose on heating to give oxides.
vi) Both Li and Mg do not form solid bicarbonates.
vii) Because of covalent character LiCl and MgCl2 are soluble in ethanol.
viii) The hydroxides, bicarbonates and fluorides of both Li and Mg are sparingly
soluble in water.
Biological importance of Na and K
i) Sodium ions participate in the transmission of nerve signals.
ii) Sodium ions also regulate flow of water across the cell membranes and in
transport of sugars and amino acids into the cells.
iii) Potassium ions are the most abundant cations within cell fluids, where they
activate many enzymes, participate in oxidation of glucose to produce ATP.
iv) Potassium ions in combination with sodium ions are responsible for
transmission of nerve signals.
v) The functional features of nerve cells depend upon the sodium potassium ion
gradient that is established in the cell.
Group 2 elements: Alkaline earth metals
(a) Atomic radii : The atomic radii of alkaline earth metals are fairly large though
smaller than the corresponding alkali metals and they increase down the group. This
is because on moving down the group, atomic radii increase primarily due to the
addition of an extra shell of electrons in each succeeding element.
(b) Ionic radii: the atoms of these elements form divalent ions which show the same
trend of increase in their size down the group.
(c) Ionization enthalpy: The alkaline earth metals have fairly low Ionizations
enthalpies though greater than those of the corresponding elements of group 1 and
this value decreases down the group.
(d) Hydration enthalpy: the Hydration enthalpies of alkaline earth metal ion
decrease as the size of the metal ion increases down the Group
Be2+ >Mg2+ >Ca2+ >Sr2+ >Ba2+
(e) Oxidation State: All the members of the family exhibit +2 oxidation state in their
compounded and the form divalent cations (M2+)
(f) Electro negativity : The electro negativity values of alkaline earth metals are
quite close to those of alkali metals, though slightly more.
(g) Metallic Character : Alkaline earth metals have stronger metallic bonds as
compared to the alkali metals present in the same period.
(h) Melting and boiling point : The melting and Boiling points of these metals are
higher than those of alkali metals present in the same period.
(i) Colouration to the flame : With the exceptio9n of beryllium and magnesium, the
rest of the elements impart characters in colour to the same flame. For example,
Be Mg Ca Sr Ba Ra
- - Brick Red Crimson Grassy Green Crimson
J) Complex formation: Generally the members do not form complexes. However,
smaller ions ( Be & Mg Ions) form complexes with the electron donor species
k) Formation of organo-metallic compounds: Both beryllium and magnesium
form a number of organo-metallic compounds containing M-C bond with certain
organic compounds. For example, magnesium reacts with alkyl halide in the
presence of dry ether to give Grignard reagent.
l) Reducing character: Alkaline earth metals are weak reducing agent than the
corresponding alkali metals which have lower ionization enthalpies and
comparatively bigger atomic sizes.
m) Reaction with oxygen: With the exception of Ba and Ra which form peroxides (
MO2) rest of the metals form normal oxides (MO) on heating with excess of
oxygen.
n) Reaction with halogens: The members of the family combine directly with
halogen at appropriate temperature to form corresponding halides.
o) Reaction with water: The members of this group are less reactive towards water
as compared to the corresponding alkali metals because these are less
electropositive in nature.
p) Reaction with hydrogen: The members except Be combine with hydrogen
directly upon heating to form metal hydrides.
Uses of some important compounds:-
(i) Caustic soda:
It is used: in soap, paper, textile, petroleum industry
ii) Sodium carbonate
It is used:
a) in glass and soap industry
b) in paper making and textile manufacturing
c) in paint and dye stuffs
d) in metal refining
e) in production of sodium compounds such as borax, caustic soda, sodium
phosphate etc.
iii) Quick lime:
It is used:
a. in the preparation of cement, glass and calcium carbide.
b. In the purification of sugar
c. In softening of hard water d. As a flux in the extraction of metal
iv) Lime stone: It is used
a) as building material
b) in the manufacture of quick lime
c) in Solvay process to prepare Na2CO3 as it is a source of CO2
d) in metallurgy for the extraction of iron
e) in toothpaste and certain cosmetics
v) Cement: It is an important building material. It is used in concrete and reinforced
concrete, in plastering and in the construction of bridges, dams and buildings.
vi) Plaster of paris: It is used
a) in making moulds for pottery and ceramics etc.
b) in surgical bandages for setting broken bones of the body
c) for making statues, models, decorative materials and black board chalk.
Biological importance of Ca and Mg
i) Magnesium ions are concentrated in animal cells and Calcium ions are
concentrated in body fluids, outside the cell.
ii) All enzymes that utilize ATP in phosphate transfer require magnesium ion
as cofactor.
iii) In green plants magnesium is present in chlorophyll.
iv) Calcium and magnesium ions are also essential for the transmission of
impulses along nerve fibres.
v) Calcium ions are important in blood clotting and are required to trigger the
contraction of muscles.
vi) Calcium ions also regulate the beating of the heart
The s- Block Element
Important points
* Groups (1 & 2) belong to the s-block of the Periodic Table.
*Group 1 consists of : lithium, sodium, potassium, rubidium, caesium and
francium and collectively known as the alkali metals.
*Group 2 include : beryllium, magnesium,calcium, strontium, barium and
radium. Except Beryllium they are known as alkaline
Physical properties-
a) Large atomic radii: The atomic radii of alkali metals are the largest in their
respective periods. These increase as we travel down the group.
b) Large ionic radii: The ionic radii increase as we move down the group due to the
addition of a new energy shell with each succeeding element.
c) Low ionization enthalpy: The ionization enthalpies decrease as we move down
the group.The ionization enthalpies of the alkali metals are the lowest due to
loosely held s- electron.
d) Hydration enthalpy: It decreases with the increase in ionic radii.The hydration
enthalpy of Li ion is the maximum and the hydration enthalpy of Cs ion is the
minimum.
e) Oxidation state: The alkali metals exhibit oxidation state of +1 in their
compounds and are strongly electropositive in character. The electropositive
character increases from Li to Cs.
f) Metallic character: The metallic character increases down the group.
g) Melting point and boiling point:: The m p and b p of alkali metals are very low
and decrease with increase in atomic number.
h) Nature of bonds formed: These metals form ionic bonds. The ionic character
increases as we down the group.
i) Flame colouration: All the alkali metals impart a charactersistic colour to the
flame.
j) Photoelectric effect: Alkali metals (except Li) exhibits photoelectric effect.
Chemical features of alkali metals:
a) Reducing character: As the ionization enthalpies of the alkali metals decrease
down the group their reducing character or reactivity in the gaseous state
increases down the group. i.e., Li < Na < K < Rb < Cs .
b) Reaction with dihydrogen: Alkali metals react with dry hydrogen at about
673 K to form crystalline hydrides which are ionic in nature and have high
melting points.
Heat
2 M + H2 2M + H-
c) Oxides and hydroxides: Alkali metals when burnt in air form different
compounds, for example the alkali metals on reaction with limited quantity of
oxygen form normal oxides ( M2O) M= Li, Na, K, Rb, Cs
d) Reaction with halogens: The members of the family combine with halogen
to form corresponding halides which are ionic crystalline solids.
Reactivity of alkali metls with particular halogen increases from Li to Cs.
e) Reaction with water: Alkali metals react with water and other compounds
containing acidic hydrogen atoms such as hydrogen halides, acetylene etc. to
liberate hydrogen gas.
f) Solubility in liquid ammonia: All alkali metals dissolve in liquid ammonia
giving deep blue solutions which are conducting in nature.
g) Reaction with sulphur and phosphorus: Alkali metals react with sulphur and
phosphorus on heating to form sulphides and phosphides respectively.
Diagonal relationship between Li and Al
Li resembles Mg mainly due to similarity in sizes of their atoms and ions. The main
points of similarity are:
i) Both are quite hard.
ii) Both LiOH and Mg(OH)2 are weak bases.
iii) Carbonates of both on heating decompose to produce oxides and
carbondioxide.
iv) Both react with nitrogen to give ionic nitrides.
v) Nitrates of both decompose on heating to give oxides.
vi) Both Li and Mg do not form solid bicarbonates.
vii) Because of covalent character LiCl and MgCl2 are soluble in ethanol.
viii) The hydroxides, bicarbonates and fluorides of both Li and Mg are sparingly
soluble in water.
Biological importance of Na and K
i) Sodium ions participate in the transmission of nerve signals.
ii) Sodium ions also regulate flow of water across the cell membranes and in
transport of sugars and amino acids into the cells.
iii) Potassium ions are the most abundant cations within cell fluids, where they
activate many enzymes, participate in oxidation of glucose to produce ATP.
iv) Potassium ions in combination with sodium ions are responsible for
transmission of nerve signals.
v) The functional features of nerve cells depend upon the sodium potassium ion
gradient that is established in the cell.
Group 2 elements: Alkaline earth metals
(a) Atomic radii : The atomic radii of alkaline earth metals are fairly large though
smaller than the corresponding alkali metals and they increase down the group. This
is because on moving down the group, atomic radii increase primarily due to the
addition of an extra shell of electrons in each succeeding element.
(b) Ionic radii: the atoms of these elements form divalent ions which show the same
trend of increase in their size down the group.
(c) Ionization enthalpy: The alkaline earth metals have fairly low Ionizations
enthalpies though greater than those of the corresponding elements of group 1 and
this value decreases down the group.
(d) Hydration enthalpy: the Hydration enthalpies of alkaline earth metal ion
decrease as the size of the metal ion increases down the Group
Be2+ >Mg2+ >Ca2+ >Sr2+ >Ba2+
(e) Oxidation State: All the members of the family exhibit +2 oxidation state in their
compounded and the form divalent cations (M2+)
(f) Electro negativity : The electro negativity values of alkaline earth metals are
quite close to those of alkali metals, though slightly more.
(g) Metallic Character : Alkaline earth metals have stronger metallic bonds as
compared to the alkali metals present in the same period.
(h) Melting and boiling point : The melting and Boiling points of these metals are
higher than those of alkali metals present in the same period.
(i) Colouration to the flame : With the exceptio9n of beryllium and magnesium, the
rest of the elements impart characters in colour to the same flame. For example,
Be Mg Ca Sr Ba Ra
- - Brick Red Crimson Grassy Green Crimson
J) Complex formation: Generally the members do not form complexes. However,
smaller ions ( Be & Mg Ions) form complexes with the electron donor species
k) Formation of organo-metallic compounds: Both beryllium and magnesium
form a number of organo-metallic compounds containing M-C bond with certain
organic compounds. For example, magnesium reacts with alkyl halide in the
presence of dry ether to give Grignard reagent.
l) Reducing character: Alkaline earth metals are weak reducing agent than the
corresponding alkali metals which have lower ionization enthalpies and
comparatively bigger atomic sizes.
m) Reaction with oxygen: With the exception of Ba and Ra which form peroxides (
MO2) rest of the metals form normal oxides (MO) on heating with excess of
oxygen.
n) Reaction with halogens: The members of the family combine directly with
halogen at appropriate temperature to form corresponding halides.
o) Reaction with water: The members of this group are less reactive towards water
as compared to the corresponding alkali metals because these are less
electropositive in nature.
p) Reaction with hydrogen: The members except Be combine with hydrogen
directly upon heating to form metal hydrides.
Uses of some important compounds:-
(i) Caustic soda:
It is used: in soap, paper, textile, petroleum industry
ii) Sodium carbonate
It is used:
a) in glass and soap industry
b) in paper making and textile manufacturing
c) in paint and dye stuffs
d) in metal refining
e) in production of sodium compounds such as borax, caustic soda, sodium
phosphate etc.
iii) Quick lime:
It is used:
a. in the preparation of cement, glass and calcium carbide.
b. In the purification of sugar
c. In softening of hard water d. As a flux in the extraction of metal
iv) Lime stone: It is used
a) as building material
b) in the manufacture of quick lime
c) in Solvay process to prepare Na2CO3 as it is a source of CO2
d) in metallurgy for the extraction of iron
e) in toothpaste and certain cosmetics
v) Cement: It is an important building material. It is used in concrete and reinforced
concrete, in plastering and in the construction of bridges, dams and buildings.
vi) Plaster of paris: It is used
a) in making moulds for pottery and ceramics etc.
b) in surgical bandages for setting broken bones of the body
c) for making statues, models, decorative materials and black board chalk.
Biological importance of Ca and Mg
i) Magnesium ions are concentrated in animal cells and Calcium ions are
concentrated in body fluids, outside the cell.
ii) All enzymes that utilize ATP in phosphate transfer require magnesium ion
as cofactor.
iii) In green plants magnesium is present in chlorophyll.
iv) Calcium and magnesium ions are also essential for the transmission of
impulses along nerve fibres.
v) Calcium ions are important in blood clotting and are required to trigger the
contraction of muscles.
vi) Calcium ions also regulate the beating of the heart
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