Alkaline earth metal

Alkaline Earth Metals
Dr. Damodar Koirala
Amarsingh Model Secondary School
Pokhara, Nepal

Chemistry
Physical / Inorganic / Organic / Industrial…
Non-metal / Metal / Bio…
Metallurgy / Alkali / Alkaline Earth…
Be/Mg/Ca/Sr/Ba/Ra
Mg and Ca compounds
2
Dr. Damodar Koirala koirala2059@gmail.com

Periodic table
3
Periodic table is divided into 4 blocks depending on
where last electron goes to

Periodic table
4

s-block elements
Group 1 (alkali) and Group 2 (alkaline earth)
which have ns1 and ns2 outermost electronic
configuration respectively
All reactive metals with low ionization energy
Lose outermost electron(s) readily to form 1+ ion
(alkali) or 2+ ion (alkaline earth)
Highly reactive hence never found pure in nature
5

Alkaline earth metals
Group 2 element with outermost electronic
configuration of ns2
The first element beryllium differ from the
rest of the members and shows diagonal
relationship to aluminium
6

General characteristics
Electronic configuration
Atomic and ionic radii
Ionization energy
Physical properties
7

Electronic configuration
All alkaline earth metals have 2 valence electron, so
ns2 outer most electronic configuration
8

Atomic and ionic radii
Def: distance from the center of the nucleus to
the boundary of the surrounding shells of
electrons
Alkaline earth metals have sizes smaller than
alkali metal but larger than other element in a
particular period of the periodic table
The atomic and ionic radii of alkaline earth metals
increases on moving down the group (Be to Ra)
9

Ionization energy
Def: The amount of energy required to remove
loosely bound electron from isolated gaseous
atom
Alkaline earth metals have I.E higher than that
alkali metal
I.E decreases down the group : Since the
increasing size outweighs the increasing nuclear
charge
10

Physical properties
Silvery white, soft (but harder than alkali metals)
and lustrous
Mp and Bp higher than alkali metal due to smaller
size
They are strong electropositive in nature
Ca, Sr and Ba impart characteristic brick red,
crimson and apple green color respectively in flame
11

Chemical properties
Reactivity towards air or oxygen
Reactivity towards water
Reactivity towards halogens
Reactivity towards hydrogen
Reactivity towards acids
Reducing nature
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Reactivity towards air and water
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Reacts with air or oxygen to form respective oxide
Mg + O2 MgO
Ca + O2 CaO

Reactivity towards water
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Reacts with water to form respective hydroxide
Ca + H2O Ca(OH)2
Be does not reacts with water
Mg reacts slowly
Calcium reacts moderately
Other reacts vigorously

Reactivity towards halogens
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Reacts with reacts with halogen to form respective
halide
Mg + Cl2 MgCl2
Ca + Cl2 CaCl2
All halides are ionic except beryllium halide is
covalent

Reactivity towards hydrogen
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Except Be all reacts with hydrogen to form hydride
Mg + H2 MgH2
Ca + H2 CaH2
Hydrogen has oxidation state of -1 in hydride

Reactivity towards acids
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Reacts with mineral acid to form hydrogen gas
Ca + HCl CaCl2 + H2
Mg + H2SO4 MgSO4 + H2

Reducing nature
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They have tendency to lose two electrons.
Ca Ca2+ + 2e-
Mg Mg2+ + 2e-
Hence they behave as strong oxidizing agent
Reducing character increases down the group

General characteristics
Solubility of hydroxides, carbonates and
sulphates of alkaline earth metals (general
trend)
Stability of carbonates and nitrate of alkaline
earth metals (general trend)
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Solubility of hydroxide
Alkaline earth metals hydroxides are less soluble in water as
compared to alkali metals.
The solubility of the alkaline earth metal hydroxides in water
increases with increase in atomic number down the group.
This is due to the fact that the lattice energy decreases down
the group due to increase in size of the alkaline earth metals
cation whereas the hydration energy of the cation remains
almost unchanged. The resultant of two effects i.e.
∆Hsolution = ∆Hlattice - ∆HHydration
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Solubility of hydroxide
All hydroxide are basic except Be(OH)2 to are
amphoteric
21

Solubility of carbonates
Solubility of carbonates of alkaline earth metals decreases
as the atomic number of the metal increases down the
group because the size of the cation increases down the
group. We know that hydration energy and lattice energy
are inversely proportional to the radii of the ions. Now, for
carbonates, the decrease in hydration energy is much
more than the decrease in lattice energy and so, their
solubility decreases down the group.
The solubility of the sulphates and carbonates follows the
order: Be>Mg>Ca>Sr>Ba
22

Solubility of sulphates
The solubility of the sulphates in water decreases down the
groups: BeSO4 and MgSO4 are highly soluble, CaSO4 is
sparingly soluble but the sulphates of Sr, Ba and Ra are virtually
insoluble.
Reason: The magnitude of the lattice energy remains almost
constant as the sulphate is so big that small increase in the size of
the cation from Be to Ba does not make any difference. However
the hydration energy decreases from Be+2 to Ba+2 appreciably as
the size of the cation increase down the group.The high
solubility of BeSO4 and MgSO4 is due to high hydration energies
due to smaller Be+2 and Mg+2 ions.
23

Stability of carbonate
Barium carbonate is thermally the most stable. On
moving down the group, the electropositive character
of alkaline earth metals increases. Due to this, their
thermal stability also increases. The smaller the
positive ion, the higher the charge density, and the
greater effect it will have on the carbonate ion.
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Stability of nitrate
Both carbonates and nitrates of Group 2 elements
become more thermally stable down the group. The
larger compounds further down require more heat
than the lighter compounds in order to decompose.
25

Molecular formula and uses
Quick lime
Bleaching powder
Magnesia
Plaster of Paris
Epsom salt
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Quick lime (CaO)
Used in steel industry to remove phosphates and silicates as slag.
It is used to make cement by mixing it with silica, alumina or
clay.
Used in making glass.
Used in lime soda process for the conversion of Na2CO3 to NaOH
& vice versa.
Used for softening water, for making slaked lime Ca(OH)2 by
treatment with water and calcium carbide CaC2.
27

Bleaching powder (CaOCl2)
Used for bleaching dirty clothes in the
laundry, as a bleaching agent for cotton and
linen in the textile industry.
It is a strong oxidizing agent, hence used as an
oxidizer in many industries.
Used as a disinfectant which is used for
disinfecting water to make potable water.
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Magnesia (MgO)
Used as an antacid to neutralize excess
stomach acid.
Used for making crucible and cupels in
metallurgical process
Used as refractory lining of metal, glass and
cement furnaces
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Plaster of Paris (CaSO4. 1/2 H2O)
Used for producing moulds for pottery and
ceramics & casts of statues & busts.
Used in surgical bandages used for plastering
broken or fractured bones
Used in dentistry.
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Epsom salt (MgSO4. 7H2O)
Used as a treatment for rashes and as a laxative.
Used as mordant for cotton in dyeing industry.
Used in preparation of fire proof textile and wood.
Anhydrous MgSO4 is used as a drying agent in organic
chemistry.
It is used in preparation of platinised asbestors which is
used as a catalyst in the contact process for the manufacture
of H2SO4.
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Alkaline earth metal

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