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s-Block Elements
Physical properties of s-block elements
Physical State
ALKALI METAL


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ALKALINE EARTH METAL

One electron in outermost shell &
General formula ns1
Francium is radioactive element
...

Alkali metals are paramagnetic,
diamagnetic and colorless in form
of ions
...

All are grayish white
...

These are diamagnetic and colorless
in form of ions or in metal states
...

Li < Na < K < Rb < Cs < Fr

ALKALINE EARTH METAL




Smaller than IA group elements,
since extra charge on nucleus
attracts the electron cloud
...

Be < Mg < Ca < Sr < Ba
In s-block elements : Be is the
smallest, Cs is the biggest

Softness
ALKALI METAL
Alkali metals are soft because ofa) Large atomic size
b) BCC crystal structure (HCP in Li)
c) Loose packing (68% packing
efficiency)
d) Weak metallic bond
 Cs is the softest metal in s-block


Atomic size ∝

ALKALINE EARTH METAL
These metals are slightly harder than
IA group elements because ofa) Smaller atomic size
b) FCC, HCP crystal structures
c) Packing efficiency 74%
d) Stronger metallic bond due to
presence of two electrons in
valence shell
...




1
1
∝ softness ∝
strength of metallic bond
melting & 𝑏𝑜𝑖𝑙𝑖𝑛𝑔 𝑝𝑜𝑖𝑛𝑡

Melting point & Boiling point
ALKALI METAL






Weak interatomic bonds are due to
their large atomic radii and presence
of only one valence electron hence
melting point and boiling point are
low
...


ALKALINE EARTH METAL






Metallic bond is stronger than IA
group due to smaller atomic size and
two electrons in valence shell hence
melting point and boiling point are
higher
...


𝑀𝑒𝑙𝑡𝑖𝑛𝑔 & 𝐵𝑜𝑖𝑙𝑖𝑛𝑔 𝑝𝑜𝑖𝑛𝑡 ∝ 𝑆𝑡𝑟𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑚𝑒𝑡𝑎𝑙𝑙𝑖𝑐 𝑏𝑜𝑛𝑑

Ionization Potential (I
...
)
ALKALI METAL






First Ionization Potential (I
...
) is very
less because of bigger atomic size
and only one electron in outer most
shell
...

Decreasing order of ionization
potential –
Li > Na > K > Rb > Cs
(1st and 2nd ionization potential
difference > 16eV)

ALKALINE EARTH METAL





First ionization potential is higher
than IA group because of smaller
atomic sixe and completely filled sorbital (stability)
Second ionization potential is lesser
than IA group
...
Electro
positive property increases from Li
to Cs

ALKALINE EARTH METAL


Their atomic size is smaller than IA
group so these are lesser electro
positive than IA group
...
Maximum capacity of
M shell is of 18 electrons but it
contains only 8 electrons, which
decreases its density
...

Density of Be is higher than Ca
and Mg because of less volume
in comparison to its mass
ii
...

Conductivity of IA < IIA

Flame test
ALKALI METAL


Alkali metals and their salts give
characteristic color to Bunsen flame
...
For example, LiCrimson red, Na- Golden yellow,
K-Violet, Rb-Red violet, Cs-Blue



hence no flame test
...
) and produces blue solution
...

Na(s) + (x+y)NH3
[Na(NH3)x]+ +
[e(NH3)y]

ALKALINE EARTH METAL







Only Ca, Sr and Ba give blue
solution of ammoniated electron
...

Dark blue color of solution becomes
fade if it is allowed to stand for a
long time; it is because of metal
amide formation
...

NH4+ + NH22NH3

Photo electric effect
ALKALI METAL




Atomic size of K, Rb and Cs is quite
large, so their ionization potential is
very low
Due to very low ionization potential
their valence shell electrons gets
excited even by absorbing visible
light
...


ALKALINE EARTH METAL


These elements do not show this
property as their atomic size is small
hence ionization potential is higher
in IA group
...

releasing electrons in water or self
 Increasing order of standard
ionic solutions)
oxidation potential is –
So these are good reducing agents,
Be < Mg < Ca < Sr < Ba
having upper most positions in
 The tendency of losing electrons
Electrochemical series
...
05eV) due to its high
hydration energy
...

Order of standard oxidation potential of s-block elements
Li > K > Ba > Sr > Ca > Na > Mg > Be
Hydration energy ∝ Charge density on ion

Hydration Energy (Heat of hydration)
ALKALI METAL





Alkali metal salts are generally
soluble in water due to hydration of
cations by water molecules
...

Li+
Na+
K+
Rb+
Cs+
 Degree of hydration decreasing
 Hydration energy decreasing
 Hydrated ion size decreasing
 Ionic conductance increasing

ALKALINE EARTH METAL





Due to smaller ionic size and higher
charge density their hydration
energy is high
...

Small cation size
ii
...

Vacant d-orbital to accept
electrons
Only Li+ can form complex
compound, due to its small size, rest
alkali metals have very less
tendency to form complex
compounds
...

Reactivity ∝ 1/Ionization Potential
Order of reactivity –
Li < Na < K < Rb < Cs
Li is stable reacts slowly with steam
...


ALKALINE EARTH METAL



Less reactive than alkali metals
...

Mg reacts with hot water
Ca, Sr, Ba react with cold water

Reaction with air
ALKALI METAL




Alkali metals get tarnish in air due
to the formation of oxide at their
surface hence they are kept in
kerosene or paraffin oil
...


ALKALINE EARTH METAL






Except Be, these metals are easily
tarnished in air, as a layer of oxide is
formed on the surface
...

In moist air, except Be all the
elements converts into carbonates
...


Reaction with oxygen
ALKALI METAL





Oxide ion [O2-] :
Li forms only Li2O (Lithium oxide)
...

Super oxide [O2-] :
K, Rb and Cs forms MO2 type oxides
(super oxides) in excess of O2
...

O2

O2

O2

M
M 2O
M 2O 2
MO2
(Li2O) (Na2O2) (KO2, RbO2, CsO2)

ALKALINE EARTH METAL







Alkaline earth metals react with O2
to form ‘MO’ type oxides
(M = Be, Mg, Ca, Sr, Ba)
But Ca, Sr and Ba due to low
ionization potential and more
reactivity, forms MO2 (peroxides) at
low temperature
...
CaO2, SrO2, BaO2
Peroxides are colored due to Lattice
defect
...

MgO is weak base
CaO, SrO & BaO are strong base

 Their stability order is –
Normal oxide > Peroxide >
Superoxide



Basic properties increases from Be
to Ba
...

Hydrides of alkali metals are
attacked by water to give back
LiH, NaH, KH, RbH, CsH

ALKALINE EARTH METAL
Except Be all the alkaline earth
metals form MH2 type hydrides on
heating directly with H2
 BeH2 is prepared by action of BeCl2
with LiAlH4
2BeCl2 + LiAlH4
2BeH2 + LiCl +
AlCl3






Thermal stability decreases
Basic property increases
Electrolysis of fused MH gives H2 at
anode
...

Be and Mg have tendency of
polymerization
...

Li is least reactive towards water
Na reacts vigorously

ALKALINE EARTH METAL






These metals react slowly with water
gives H2 and metal hydroxides
...

Mg reacts only with hot water
...

Order of reactivity





K reacts producing a flame
Rb, Cs reacts explosively
These metals also react with alcohol
give alkoxide and H2
2Li + 2C2H5OH
2C2H5OLi + H2
Monoxides give strongly alkaline
solution with water
M2O + H2O
2MOH



Ba > Sr > Ca > Mg > Be
From Be(OH)2 to Ba(OH)2 basic
property and stability increases
...
Hence it hydrolyses with water
while rest are ionic so do not
hydrolyze
...

KI + I2
CsBr + Br2

On ionization

KI3

CsBr3








K+ + I3-

Alkaline earth metals react with X to
form MX2
...
(BeCl2, MgCl2, CaCl2 etc
...

Hydrolytic nature of these halides
decreases from BeCl2 to BaCl2
BeCl2 and MgCl2 are covalent in
nature
...

Stability increases from LiNO3 to

ALKALINE EARTH METAL



All the alkaline metals forms MCO3
type carbonates
...
LiNO3 decomposes into
Lithium oxide & NO2 on heating
...

∆
MNO3
2MNO2 + O2
Nitrite

Nitrates
ALKALI METAL





ALKALINE EARTH METAL

Alkali metals form MNO3 type
nitrates
Stability increases from LiNO3 to
CsNO3
...

∆
4LiNO3 Oxide 2Li2O + 4NO2 + O2






Other nitrates on heating to give
nitrite and oxygen
...

Stability increases from Be(NO3)2 to
Ba(NO3)2 but these are less stable
than IA group, due to smaller
atomic size
...


Nitrides
ALKALI METAL


Only Li react directly with N2 to
form nitride which gives NH3 on
reacting with water
...

These metals react with other metals
to give mixed metals (alloys)



Shows same properties
...

 All alkali metal sulphates are ionic
...

Li2SO4 < Na2SO4 < K2SO4 < Rb2SO4 <
Cs2SO4
 Li2SO4 is least soluble in water
...
gives double salts called alum
...
M2(SO4)3
...

 Ionic nature of alkaline metal
sulphate increased from Be to Ba
...




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