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Ch.41notes – P.1
Ch.41 – s-Block elements
A. Characteristic properties of the s-block elements
1. Metallic character
* s-Block elements have
ionization energies and
electronegativities.
They are therefore very
, with a tendency to lose their
outer electrons.
*
They are all
__________They are silvery coloured and tarnish rapidly in air.
*
These metals show
metallic bonding when compared with
other metals because only one or two valence electrons are involved in the
bonding.
 They are
_________ and can be cut with a knife
 They have_______ melting and boiling points, low hardness and densities
*
Group II metals
vs Group I metals
2. Formation of basic oxides and hydroxides
*
The oxides of s-block elements are usually combustion products of the metals.
*
The hydroxides are usually products of reactions of the oxides with
water/steam.
*
The oxides and hydroxides of s-block elements are all _____________ .
*
Basicity of oxides and hydroxides
down the group.
Ch.41notes – P.2
3. Bonding type and oxidation state
*
The s-block elements form compounds that are predominantly
in
nature.
*
They exhibit only one fixed oxidation state in their compounds
 Group I metals :
 Group II metals :
[Explanation in terms of ionization energies and lattice energies]
4. Characteristic flame colours of salts
*
Salts of Group I and Group II elements exhibit characteristic flame colours :
Element
Flame Colour
Element
Lithium
Beryllium
Sodium
Magnesium
Potassium
Calcium
Rubidium
Strontium
Caesium
Barium
Flame Colour
5. Weak tendency to form complexes
*
Ions of d-block metals have _______________ and hence they can form
complexes by ________________ bond formation.
*
Ions of s-block metals __________ form complexes because they do not have
vacant d-orbitals.
*
Ions of s-block metals may be surrounded by polar solvent molecules (such as
water), with the negative ends of their dipoles towards the positive metal ion.
This is called
of ions (or
of ions if
water is used as the solvent). However, such association is just the
electrostatic attraction between the positive ion and the dipoles.
Ch.41notes – P.3
B. Variation in properties of the s-block elements
1. Atomic radii
*
Variation in atomic radii (metallic radii) and ionic radii :
*
Ionic radius is always
than atomic radius for Group I
and II elements
*
In general, atomic and ionic radii
on descending the
groups
*
Atomic and ionic radii of Group I elements are
than
Group II elements
*
The pairs of ions
_______
and
_______ , or ______
have been found to have similar ionic radii.
and
______
Ch.41notes – P.4
2. Ionization energies
*
Variation in ionization energies
*
Ionization energies
on descending both groups
3. Melting points
*
Variation in melting points
*
In general, the stronger
the metallic bond, the
the melting
point is.
*
Factors affecting strength of metallic bond :
   

   

   
*
Group II metals have
*
In general, melting points of Group I and II metals
groups
melting point than Group I metals.
since the strength of metallic bond
descending both groups
down the
on
Ch.41notes – P.5
4. Hydration energies of ions
*
Variation in hydration energies
*
Magnitudes of hydration energies of the cations
on
descending both groups.
*
Magnitudes of hydration energies of Group II metal ions are
_______
than Group I metal ions
5. Chemical reactivities
a) General trend in chemical reactivities
*
s-Block elements are
*
The reducing power
strong _______________________.
down the groups.
[ Reason ]
M(s) 
M(g) 
M+(g)
On descending the groups, the atomic size
(1)
and hence
tendency to break down the metallic crystal
( strength of metallic bond
(2)
)
tendency to release outermost electron
( ionization energy
)
Ch.41notes – P.6
b) Reactions with some substances
(i) Reactions with oxygen/air
* When freshly cut, s-block metals have a bright lustre.
_____________
However, they
readily when they come into contact with oxygen in air.
Thus except beryllium
and magnesium, the s-clock metals are usually
stored under __________________ to prevent contact with the atmosphere.
Beryllium and magnesium form a protective oxide layer and thus tarnish
comparatively slowly.
*
All these metals burn brilliantly in air to form one or more of the three types
of oxide.
Metal
Combustion products
Normal oxide
Peroxide
Superoxide
Li
Na
K
Rb
Cs
Be
Mg
Ca
Sr
Ba
(ii) Reactions with water
* Group I metals react with water to give hydrogen gas and alkaline solutions.
e.g. 2 Na
*
The reactivity
*
Group II metals have
+
2 H 2O 
2 NaOH
+
H2
down both groups.
reactivity than Group I metals.
(iii)Reactions with hydrogen
*
All the s-block metals except beryllium react directly with hydrogen to
produce _____________. (Magnesium requires high pressure.)
*
The reactivity
down both groups.
Ch.41notes – P.7
(iv) Reactions with chlorine
*
All s-block metals combine directly with chlorine to produce ____________.
*
e.g.
2 Na
+
Cl2

2 NaCl
C. Variation in properties of the compounds of s-block elements
1. Reactions of the oxides
*
In general, oxides of s-block metals are
*
Group I oxides are generally
*
Basicity
*
All
Group
in nature
basic than Group II oxides.
down both groups.
I
oxides
form
react
exothermically
with
water
to
It is almost insoluble in water or in acids.
Its
.
e.g.
*
BeO is _______________.
amphoteric nature is only shown in hot acids or alkalis :
*
MgO is almost inert towards water, but dissolves in acids to give salts
e.g.
*
Other Group II oxides react readily with water giving slightly alkaline
solutions
e.g.
Ch.41notes – P.8
2. Reactions of the hydrides
*
They all react readily with water to give the metal
and
______________.
e.g.
*
The reactivity
down both groups.
*
Group II hydrides are
reactive than Group I hydrides.
3. Reactions of the chlorides
*
Chlorides of Group I metals are all readily ______________ in water.
*
Lithium chloride is markedly _______________, whereas other Group I
chlorides are ___________________.
*
BeCl2
is ___________ and hence undergoes hydrolysis in water giving an
___________
*
solution.
Other Group II chlorides just _____________ in water.
Ch.41notes – P.9
4. Relative thermal stability of the carbonates and hydroxides
*
Thermal stability refers to the decomposition of the compound on heating.
e.g.
*
The thermal stability of an ionic compound depends on the
and the
___________
___________
of the ions.
The attraction between the ions is stronger if the charge is
size is
and the
.
On descending a group, as the size of metal ion
, the
interionic attraction becomes
stability of the compound
and thus the thermal
becomes
.
true for many ionic compounds of s-block
This is
elements, such as
_____________, ______________etc.
*
However, for _____________ and _____________, the thermal stability
______________
*
on descending the groups.
Carbonate and hydroxide are _________________
anions. For compounds
with such anions,
also
the
_____________________
thermal
stability
is
affected
of the cations. If the cation has a
polarising power (i.e.
size and
by
the
greater
________ charge), it will
___________ the electron cloud of the neighbouring large anion to a
extent. The compound become _____________
and is
greater
more liable
to
decomposition to the smaller anions, so that the attraction between cations and
the smaller oxide anions can become greater.
Hence the thermal stability of carbonates and hydroxides of both Group I and
II metals __________________ down the group.
*
The Group II metal ions are much
than those of Group I
metal ions and have a
consequently
Group II metals are therefore
metals.
. Their polarizing power is
.
Carbonates and hydroxides of
than those of Group I
Ch.41notes – P.10
 Carbonate
*
All group I carbonates except lithium carbonate can withstand a temperature
around 800oC.
*
Lithium carbonate decomposes at around 700oC:
Li2CO3(s) 
This is due to the _____________________ of lithium ion, which leads to a
____________________________________
and
make
the
carbonate
unstable.
*
Due the high ____________________________, group II carbonates
decompose upon heating:
BeCO3(s) 
MgCO3(s) 
CaCO3(s) 
SrCO3(s) 
BaCO3(s) 
*
Going down each group, as size of the cation _________________, the
polarizing power _______________, and hence the carbonates become
_____________________.
 Hydroxide
*
All group I hydroxides except lithium hydroxide are stable when heated.
*
Due the same reasons, lithium hydroxide decomposes upon heating:
LiOH(s) 
*
The group II hydroxides decompose upon heating; its trend of stability can be
revealed from the enthalpy changes:
Be(OH)2 (s) 
△H =
Mg(OH)2 (s) 
△H =
Ca(OH)2 (s) 
△H =
Sr(OH)2 (s) 
△H =
Ba(OH)2 (s) 
△H =
Ch.41notes – P.11
5. Relative solubility of the sulphates and hydroxides
*
_________________________________ can be used for comparing the
relative solubility of the ionic compounds.
M+(aq)
MX(s)
+ X-(aq)
M+(g) + X-(g)
*
If the magnitude of Hhydration
Hsolution
is
is greater than that of Hlattice , then
negative (exothermic), and the compound will, in general,
be ___________.
*
Group I metal ions have
than



charges
and
sizes
Group II metal ions.
Hlattice
of their compounds are
in magnitude
than
those of Group II compounds.
Hsolution
of Group II compounds is
negative .
Consequently, sulphates and hydroxides of Group I metals are
than those of Group II metals.
__________
Ch.41notes – P.12
*
In comparing within the same group, the________ of an ion is a crucial factor.
*
The hydration enthalpy is dependent on the charge/radius ratio of the
___________.
The lattice enthalpy is dependent on the _________ of the radii, i.e. r+ + r-.
*
For the hydroxide of Group II metals, the __________ of the anions and
cations are of the ___________________ of magnitude.
Down the group, __________ energy is required to break the lattice as the size
of cation increases, but the change in
As a result,
Hhydration
is comparatively small.
Hsolution becomes
negative and the
solubility of Group II hydroxides
e.g. Solubility of Mg(OH)2
*
down the group.
Ca(OH)2
Sr(OH)2
Ba(OH)2
For the sulphates of Group II metals, since sulphate is a _______________,
the cations are much smaller.
Down the group, the change in size of the
cations does not cause a significant change in Hlattice , but Hhydration
become __________________ (due to increasing ionic size). As a result,
Hsolution
becomes _________________________ and the solubility of
Group II sulphates _____________________
e.g. Solubility of
MgSO4
CaSO4
down the group.
SrSO4
BaSO4
Ch.41notes – P.13
D. Uses of the compounds of the s-block elements
*
Sodium hydroxide is used in the _________________ of fats and oils to produce
soap.
CH3(CH2)16-COO-CH2
CH3(CH2)16-COO-CH

+ 3 NaOH
CH3(CH2)16-COO-CH2
*
Sodium hydroxide is also used domestically to clear ____________________.
*
Sodium carbonate is used in the manufacture of _________. Soda glass is a
mixture of sodium silicate and calcium silicate, which is made by fusing the
carbonate with silica (from sand)at 1500oC.
CaCO3
Na2CO3
*
Sodium
+
+
carbonate

CaSiO3
SiO2

Na2SiO3
also
used
SiO2
is
in
+
+
CO2
CO2
_______________________
and
_____________________ to precipitate Mg2+ and Ca2+.
* Sodium hydrogencarbonate is commonly found in _________________ which also
contains a solid acid.
Besides,
sodium
hydrogencarbonate
also
undergoes
_________________
_____________________ at high temperature :
*
Sodium hydrogencarbonate is also used extensively in __________________.
*
Potassium hydroxide is used for long-lasting __________________________ .
Ch.41notes – P.14
* Magnesium
hydroxide
is
______________________.
an
active
ingredient
in
antacid
such
as
The magnesium hydroxide is used to neutralize
the excess acid in the stomach.
* Calcium hydroxide (slaked lime ) can be used to neutralize the acids in
____________________________ :
It can also be spread onto _____________________________ to neutralize the
effects of acid rain.
* Strontium compounds are used in _____________because they will give a
persistent and intensive red flame when burnt.