Download Main Group and Transition Elements (15 h)

Main Group and
Transition Elements
(15 h)
Chemistry of s,p,d, and f block elements
Dr. Shashikala Rajapakse
E-mail: [email protected]
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Recommended reading:
1. Greenwood, N. N. and Earnshaw, A., (1997)
Chemistry of the Elements, Oxford.
2. Shriver, D. F., Atkins, P.W. and Langford, C.H.,
(1991) Inorganic Chemistry, Oxford.
3. Liptrot, G. F., (1993) Inorganic Chemistry, London
Mills and Boon.
4. Lee, J. D.,(1991), Concise Inorganic Chemistry
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The periodic table is the most important
tool in the chemist’s toolbox!
The Periodic Table, every chemist’s best friend !
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You will learn…………..
1. Properties of the elements in the periodic table
2. The periodic trends of physical and chemical
properties of the elements.
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Dmitri Mendeleev
In 1869 he published a table of
the elements organized by
increasing atomic mass.
1834 - 1907
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The Modern Periodic Table
Element Organization
The Periodic Law:
Elements are arranged by atomic #,
Why elements are arranged by atomic # ?
The elements with similar properties appear at
regular intervals
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Periodic table of the elements
(columns)
Groups
Periods
(rows)
Elements are presented in the periodic table by
increasing values of their atomic numbers / the
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number of protons in their atomic nuclei.
Symbols in Table
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periodic table blocks
named according to the subshell in which the
"last" electron resides.
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Main Group Elements (s+p)
The main group elements of the periodic
table are groups 1, 2 and 13 through 18
These groups contain the most naturally
abundant elements, comprise 80 percent of the
earth's crust and are the most important for life.
d block elements:
groups 3-12
f block elements:
Lanthanides and Actinides
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Members of the s-Block Elements
Valence electron/s are in s orbital
1
2
Li
Be
Na
Mg
K
Ca
Rb
Sr
Cs
Ba
Fr
Ra
Group 1 - Alkali metals
Group 2 - Alkaline earth metals
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Group 1 - Alkali metals (ns1) – Except H
form oxides and hydroxides that dissolve in water to
give alkaline solutions
Li
Na
Lithium – 1s2, 2s1 or [He]2s1
Sodium- [Ne]3s1
K
Potassium- [Ar]4s1
Rb
Rubidium - [Kr]5s1
Cs
Cesium - [Xe]6s1
Fr
Francium - [Rn]7s1
valence electron
configuration is ns1
n = the period number.
Fr is radioactive
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Extraction of alkali metals
s-block are all extremely powerful reducing agents,
so much so that they never occur naturally in the
free state.
The metals are all isolated by electrolysis of a
fused salt, usually the fused halides
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Properties of alkali metals
Physical
Properties
1.
2.
3.
4.
5.
6.
Chemical
Properties
Ionization energy
Reactivity (reaction with
Hydration energy
H2O, halogen etc…)
Lattice energy
Conductivity
Melting point/boiling points
Solubility
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Atomic radii (nm)
The sizes of the atoms increase due to the effect of
extra shells of electrons being added.
Li
0.152
Na
0.186
K
0.231
Rb
0.244
Cs
0.262
Fr
0.270
Atomic radius/nm
Fr
Li
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Ionization energies (I. E.)
The energy required to remove the most loosely
bound electron from an isolated gaseous atom
1 st Ionization energy
Energy required to remove the outer most electron and
convert M to M+
M
M+
+
e
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e.g.
1 st Ionization energy of Na = 494 kJ/mol
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1 st Ionization energy
1st I.E.
(kJ/mol)
Group I 1st I.E.
600
500
400
300
Li Na
K
Rb
Cs
2nd I.E.
Li
519
7300
Na
494
4560
K
418
3070
Rb
402
2370
Cs
376
2420
I.E. decreases as the group is descended.
As atomic radius increases, the outer e is
further away from the well-shielded nucleus.
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Ionization energies (kJ/mol)
Group I 1st I.E. 2nd I.E.
Li
519
7300
Na
494
4560
K
418
3070
Rb
402
2370
Cs
376
2420
2 nd I.E. >>> 1 st I.E.
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Metallic character
Metallic bonding is the electrostatic attractive
forces between the delocalized electrons,
called conduction electrons, gathered in an
"electron sea", and the positively charged metal
ions.
• High tendency to
lose e- to form
positive ions
• Metallic character
increases down the
group
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Melting and Boiling points
Li
Na
K
Rb
Melting point
(0C)
Boiling point
(0C)
181
98
63
39
1347
881
766
688
Trend: The melting/boiling points of group I metals
decrease down the group.
.
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Characteristic flame colors
This property of alkali metals is used in their identification.
Element
Flame Colour
Element
Flame Colour
Lithium
red
Calcium
brick redNa
Sodium
golden yellow
Strontium
blood red
Potassium
lilac
Rubidium
Red-violet
Caesium
violet
Barium
Na
apple green
K
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Flame test
The metal salt is mixed with
concentrated HCl acid
Sample of the mixture
is heated strongly in a
bunsen flame on the end of
a cleaned nichrome wire (or
platinum if you can afford it!)
sample
HCl(aq)
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Summary
Li+
Na+
K+
Rb+
Cs+
Li+ most hydrated
Size increases
Cs+ Least hydrated
Relative ionic radii Cs+ > Rb+ > K+ > Na+ > Li+
Relative hydrated ionic radii Li+ > Na+ > K+ > Rb+ > Cs+
Ionic mobility in aqueous solution Cs+ > Rb+ > K+ > Na+ > Li+
Relative conducting power Cs+ > Rb+ > K+ > Na+ > Li+
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Hydration Enthalpy (∆Hhydra)
It is the energy liberated at the time of hydration.
M+(g) + aqueous → M+(aq) + heat
M+
Forms bonds with H2O = release energy
kJ/mol
∆Hhydra = (-)
-600
As the degree of hydration
decreases as we move -300
down the period, hydration
energy decreases from Li
to Cs.
Li+ Na+
K+
Rb+ Cs+
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Ionic mobilities and hydration
Ion
Li+
Cs+
Ionic radius /A0
0.76
1.67
Ionic radius (hydrated) / A0
3.40
2.28
Approx.
25.3
9.9
Ionic mobility at infinite dilution
33.5
68.0
∆H hydration (kJ mol-1)
-544
-293
Hydration number
Hydration number: the average number of water
molecules associated with the metal ion.
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Q. 1
Hydration energy of Lithium ion is maximum among
alkali metal ions. Why?
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Factors affecting lattice enthalpy
kJ/mol
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Chemical properties of
group 1 elements
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Q. 2
Why are the group 1 alkali metals like
lithium, sodium and potassium stored
under oil?
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Group 1 metals dissolve in liquid ammonia to give
blue solutions containing solvated electrons
Na0 + NH3→ Na+ + e- + NH3
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If the blue solution is allowed to stand, the color
slowly fades until it disappears owing to the
formation of a metal amide.
-
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Q.3
Write a chemical equation for the reaction between
pure liquid NH3 and Na metal
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Tendency to form complexes
Complex formation is a common feature of d-block
element. e.g. Co(NH3)63+
A complex is a polyatomic ion or neutral molecule
formed when moleculat group or ionic groups (called
ligands) form dative covalent bonds with a central
metal atom or cation.
The formation of
:NH3
complexes required the
H3N:
:NH3
presence of vacant lowCo
lying d-orbitals which is
H3N:
:NH3
available for the transition
metals (d-block elements).
:NH3
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Weak tendency to form complexes
(group 1 elements)
s-block metal ions have no low energy vacant
d orbital available for bonding with lone pairs of
surrounding ligands, they rarely form complexes.
With crown ethers
Crown ethers are specialized cyclic polyethers that
surround specific metal ions to form a cyclic complex
18-crown-6
1,4,7,10,13,16-hexaoxacyclooctadecane
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Crown ether molecules can trap metal ions by
forming ion-dipole bonds with them, resulting in an
entity known as host-guest complex
12-crown-4
15-crown-5
18-crown-6
Many inorganic salts can be made soluble in
non polar organic solvents by complexing them
with an appropriate crown ether.
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