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SLOs
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Topic
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4.1
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Kinetic
Molecular Theory:
This
Theory describes the behavior of different stats of matter. However it is a
best model for an ideal gas. So, it is also called kinetic molecular theory
of gases.
The main postulates of this theory are
as given below:
Postulates:
1)
Gases are composed of a large number of particles
that behave like hard, spherical
objects in a state of constant, random motion.
2)
These particles move in a straight line until they
collide with another particle or the walls of the container.
3)
These particles are much smaller than the distance
between particles. Most of the volume of a gas is therefore empty space.
4)
There is no force of attraction between gas
particles or between the particles and the walls of the container.
5)
Collisions between gas particles or collisions
with the walls of the container are perfectly elastic. None of the energy of
a gas particle is lost when it collides with another particle or with the
walls of the container.
6)
The average kinetic energy of a collection of gas
particles depends on the temperature of the gas and nothing else.
7)
Gases exert pressure which the result of collision of molecule
of gas to the walls of container
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4.1.2
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GAS
LAW:
The gases have volume,
pressure, temperature etc. All these quantity are related to one and another
according to some statement, called “The gas laws”.. some of the important
gas laws are as follow:
ü Boyle’s law.
ü Charle’s law.
ü Avogadro’s
law.
ü Graham’s law
of diffusion.
ü Dalton’s law
of partial pressure.
Boyle’s
Law:
Robert
Boyle, in 1662, showed the relationship between the pressure and the volume
of a gas at constant temperature. This is called “BOYLE’S LAW.”
Statement
1:
According
to the Boyle’s law
“At
constant temperature, the volume of a given mass of gas is inversely
proportional to the pressure applied on it.”
Explanation:
It
means that the increase in pressure would result in a decrease of volume of a
gas, similarly the decrease in pressured result in the increase in the
volume.
Simply we can say, if the
pressure is doubled, the volume becomes half and if the pressure is reduce to
half, the volume becomes double.
Mathematic
Expression:
Mathematically, Boyle’s law can
be expressed
as
 (at constant
temperature) ð P x V =K
Where K = proportionality constant.
This equation gives another
statement Boyle’s law, which is as under:
Statement
2:
“At
constant temperature, the product of pressure and a volume of a given mass of
a gas is always constant.”
Therefore; if
P1 & V1
are initial pressure & volume, &
P2 & V2
are changed pressure & volume,
Then P1V1=P2V2 This
is called “Boyle’s law equation
Graphical
Representation:
When
pressure’ P’ of a given mass of a gas is plotted against it’s volume ‘V’, a
parabolic curve is obtained, showing the decrease in volume in increasing
temperature. On the contrary, when
pressure ‘P’ of a given mass oa a gas is plotted against reciprocal pf volume
i.e.
 a straight line is
obtained. This confirms the direct relationship between ‘P’ and ‘’.
Limitations of Boyle’s law: This law is
not obeyed by gases under conditions of high pressure & law temperature.
CHARLE’S
LAW:
In
1787, a French physicist, Charles’s showed the relationship between the
volume of a given mass of a gas and it’s temperature at a constant pressure.
This law is called Charles’s law
STATEMENT # 1:
According
to this law:
“At constant pressure, the
volume of a given mass of a gas is directly proportional to the absolute temperature.”
EXPLAINATION:
It
means, if the pressure is kept constant, the increase in temperature would
result also in increase the volume of a given mass of a gas. Similarly, the
decrease in temperature results also in decrease in the volume of a gas.
MATHEMATICAL
EXPRESSION:
Mathematically, Charle’s law can be
expressed as:
VaT (At. Constant Pressure)
OR V=KT OR
This expression gives another
statement of Charle’s law, which is as under.
STATEMENT#2:
“At
constant pressure, the ratio of volume to the absolute temperature of given
mass of a gas is always constant.”
Therefore; if
V1&T1
are initial volume & temperature & V2 &T2
are changed volume & temperature.
Then
This is called “CHARLES’S law
equation.”
EXPERIMENTAL
VERIFICATION:
Consider
a gas cylinder fitted with a move able piston. The volume of the gas enclosed
in the cylinder is V1 at temp. T1 . When the gas is
heated to T2, its volume is increase to V2 by moving
the piston upward. It the pressure on the piston is kept constant, then it is
observed that the ratio between V1 andT1 is equal to
the ratio V2 and T2.i.e.
This verifies the Charle’s law.
     
-300
-200 -100 0 100
200 300
GRAHAM’S LAW
OF DIFFUSION:
Diffusion
is the natural process by which gases intermix with one another to form a
homogenous mixture.
In
1833, Graham established a relation ship between the rate of diffusion of
gases and their densities which is terms as “Gaham’s law of diffusion”.
STATEMENT:
According
to this law,
“The rates of
diffusion of gases are inversely proportional to the square root of their
densities under same condition of temperature and pressure”.
MATHEMATICAL Expression:
Mathematically,
graham’s law can be expressed as:
OR
Where r = rate of diffusion of gas,
d= density of gas,
K= Proportionality
constant.
Suppose two gases with densities d1
& d2, diffuse into each other. If the rate of diffusion of the
gases are r1 & r2 respectively, then according to
graham’s law:
For gas 1,
& For gas 2,
By
combining the two equations, we get
Since the density of a gas is
proportional to its molecular mass, so Graham’s law may also be expressed as:
Experimental Verification:
Take
a 100 cm long glass tube. Plug one end of it with a piece of cotton soaked in
NH3 solution and the other with a piece of cotton soaked in HCl
solution as shown in the diagram.
The
vapours of NH3 and HCl escape into the glass tube simultaneously.
A white ring of NH4Cl appears at the meeting point of the two gases.
Measure out the distance of te white ring from two ends.
Suppose,
the distance covered by NH3 = 60 cm
&
the distance covered by HCl = 40 cm
Since
the time ‘t’ is the same, therefore The rate of diffusion of NH3
gas =
&
the rate of diffusion of HCl gas =
\ Molecular Mass of NH3
=
 = 17
&
Molecular Mass of HCl =
 = 36.5
\ According to Graham’s law of
diffusion,
 
1.5 = 1.5
Since
L.H.S. = R.H.S., therefore Graham’s law of diffusion of gases is verified.
Dalton’s Law of Partial Pressure:
The
behavior observed, when two or more gases are placed in same container is
summarize in Dalton’s Law of Partial Pressure.
Statement: In 1801, Dalton’s found that
“The total pressure of a gaseous
mixture is the sum of the
partial pressure, exerted by each of the
gases present in
the mixture”.
Mathematical
Expression:
Mathematically
this law can be expressed as,
P
= P1 + P2 + P3 + ………………
Where
P =
Total pressure of gaseous mixture
P1 = Partial Pressure of gas 1.
P2 = Partial Pressure of gas 2.
P3 = Partial Pressure of gas 3.
Explanation:
When
two or more gases which do not react chemically, are mixed in the same container,
then each gas will exert the same pressure as it would exert if it alone
occupied the volume containing the mixed gases, under the same condition.
This portion of the total pressure of a mixture is known as PARTIAL PRESSURE.
Dalton observed that the total pressure of a mixture of different gases is
always equal to the sum of individual or partial pressure of each gas present
in a mixture.
Experimental
Verification:
Let
us suppose that two different gases A & B are confined in two separate
compartments as shown, in the figure. Both the compartments are of same size
with a pressure measuring device.
Now
suppose that the pressure of a gas is ‘A’ is 800 torr and that of gas ‘B’ is
900 torr in their separate compartments. If gas ‘A’ was transferred into the
compartment ‘B’ with the help of a movable piston through the total pressure
in this compartment would be the sum of the original pressure in the two
compartments when the gases were occupying same volume separately.
i.e. Ptotal = PA + PB
1700 = 800 + 900
1700 = 1700
Hence,
law is verified.
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4.1.3
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KMT
EXPLAINATION FOR BOYLE’S LAW
Boyle’s
law can easily be explained on the basis of the kinetic theory of gases, when
the volume of a given amount of a gas is decrease, there is more crowding of
the molecules in that space. This result in more frequent collision between
the molecules and the walls of the container and thus the pressure of the gas
is increased and vise-versa.
Limitations of Boyle’s law: This law is
not obeyed by gases under conditions of high pressure & law temperature.
KMT
EXPLAINATION FOR CHARLES’ LAW
This
law can be easily explained with the help of Kinetic molecular theory as:
An
increase in temperature increases the K.E. of gas molecules which results in
their more collision per second against the walls of the container. But if
the pressure is kept constant the extra force of the colliding molecules is
utilized for the expansion of gas, i.e. increase in volume.
KMT
EXPLAINATION FOR AVOGADRO ‘S LAW
It
means that, if we take different sample of different gases at same
temperature and pressure, then if the volume of each gas sample is equal, the
no. of molecules of each sample will be also equal evidently, if we increase
the volume of gas sample, the no, of molecules will be also increase.
Avogadro’s
also found that at the some condition of temperature and pressure, the one
mole of any gas occupies always 22.4dm3
volume, this volume is called molar gas volume. Also, this volume contain
always constant no. of particles of gas, and its value is 6.02 x 1023.
This value is called Avagadro’s number.
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4.2.1
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Charles’s
law can also be explained by graphical method, if the volume of the given
mass of a gas is plotted against its absolute temperature values at a
constant pressure, a straight line is obtained, showing the direct
relationship between ‘V’ and ’T’.
If
the straight line is extra plotted it intercepts the temperature axis at
-273.16oC. This temperature is called “ABSOLUTE ZERO”.
ABSOLUTE ZERO:
It
is a hypothetical temperature, at which the volume of all gases become zero.
Its value is -273.16oC.This temperature can never be achieved.
The
scale on which -273.16oC is taken as zero is called “KELVIN SCALE”
and is indicated by K. Centigrade is related to Kelvin scale as;
oK = oC
+ 273
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4.2.2
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NUMBERICAL
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4.3.1
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AVAGADRO’S LAW:
In
1811, Amadeo Avagadro stated the relation ship between the volume and the no.
of molecules of the gas. This is called “AVAGADRO’S LAW”.
Statement:
According
to Avogadro’s law;“The Volume of a gas is directly proportional to the number
of molecules of the gas at constant temperature & pressure”.
Explanation:
It
means that, if we take different sample of different gases at same
temperature and pressure, then if the volume of each gas sample is equal, the
no. of molecules of each sample will be also equal evidently, if we increase
the volume of gas sample, the no, of molecules will be also increase.
Avogadro’s
also found that at the some condition of temperature and pressure, the one
mole of any gas occupies always 22.4dm3
volume, this volume is called molar gas volume. Also, this volume contain
always constant no. of particles of gas, and its value is 6.02 x 1023.
This value is called Avagadro’s number.
Mathematical
Expression:
Mathematically,
Avogadro’s law can be written as,
V
µ
n
OR
V = K n
Where
n= no. of molecules of gas
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4.4.1
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General Gas
Equation:
Boyle’s
law, Charles law and Avogadro’s law may be combined together to give a
general relation between the pressure, volume, temperature and no. of moles
of a gas. This relationship is called “General
Gas Equation”
According to Boyle’s law
According to Charle’s law V µ T
On
combining these three laws. We get
OR
OR PV= nRT
This expression is called ‘GENERAL
GAS EQUATION’. Where ‘R’ is a proportionally constant and is called gas
constant.
For
1mole of a gas, n=1.
\PV=RT
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4.4.2
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When
the temperature of a gas changes from T1 to T2, then
its volume as well as pressure changes from V1 to V2
and P1 to P2.
\ For initial
state:
& For final state:
Combine
these two, we have
This
relationship is used to solve problems regarding changes of volume of gases,
due to the changes in the pressure & temperature.
VALUES &
UNIT’S OF ‘R’:
(a)
According to Avagadro’s law, at S.T.P the one mole
of any gas occupies a volume of 22.4dm3.
i.e. T=0˚C=273oK , P=1atm., n=1mole and V=22.4dm3
Then the value and unit of gas
constant will be;
   
(b)
When ‘P’ is expressed in
 and volume ‘V’ in m3,then at S.T.P,
P=101300
,V=0.0224m3 , n=1mol. And T=273oK.
Then the value and
unit of gas constant will be.
\
 
R
= 8.314 N.m / mole x K
R
= 8.314 J/mole x K
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4.4.3
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U
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4.4.4
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A
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4.5
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4.5.1
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Deviations
from ideal behavior
Ideal gas : a gas which obeys the general gas
equation and other gas laws under all conditions of temperature and pressure
is known as Ideal gas or perfect gas.
The molecules of an ideal gas :
(i)
Occupy negligible or no volume
(ii)
Have no inter-molecular
attractive forces.
Real gas : a gas
which does not obeys general gas
equation and all other gas laws strictly but tends towards ideality at low
pressure and high temperature is knonw as real gas .
Cause
of deviations from ideal behavior
In order to explain deviations from ideal behavior
,Vander waal pointed out that the following two assumptions in kinetic theory
are faulty.
(i)
The volume occupied by the gas
molecules themselves is negligible as compared to total volume of the gas
The above assumption
is nearly valid if the pressure is low .At low pressure ,the gas molecules
are widely separated and the free
space between the molecules is very large in comparison to the actual volume
of molecules of the gas. Under such condition, the volume of the gas
molecules can be neglected in comparison to the total volume. At the high
pressure, the molecules of gas are relatively closed together and the total
volume is significantly less . However
the actual volume of the gas
molecules remains unchanged because the gas molecules are
incompressible. Under these conditions, the volume of a real gas is larger than that for an ideal
gas.
(ii)
The molecules of a gas exert no
appreciable attraction upon each other .
This assumption is
nearly valid when the pressure is low and the temperature is high so
that the molecules are far away from
each other . if the pressure is high and the temperature is low , the volume
of the gas decrease .Gas molecules come closer to each other .The attractive
force between the gas molecules under
these conditions are quite appreciable and can not neglected .
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4.5.2
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Numerical for
ideal equation
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4.6
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4.6.1
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Sunday, December 11, 2011
Notes of AKUEB
Notes of BIEK
CHEMICAL
BOND
The attractive forces
due to energy barrier that hold atoms together in a compound is known as
chemical bond. There are various kinds chemical bonds like ionic covalent but
all involve the stable configuration of
atom or ion.
Ionic bond:
This
type of chemical bond is proposed by kossel in 1916.
“A chemical bond
which is formed as a result of complete transfer of electron from one atom to
another so that both atom acquire inert gas configuration is called ionic or
electro covalent bond”
The atom, which can
loose electrons, is called electropositive and atom which can gain electron is
called electronegative. These appositively charged ion are held together
electrostatic force of attraction.
Condition For
Ionic Bonding
1- The
electro negativity difference between the combing elements should be greater
than 1.7.
2- The
energy evolved in the third step is greater than the energy absorb in the first
step.
Ionic or
electrovalent bond is generally formed between elements of group 1A, 11A
(metal) and group V1A ,V11A(non metal).this is due to low ionization potential
of metal and high E.A of non metals for e.g.NaCl,CaBr2,MgO,KI.
Explanation:
For
the formation of ionic bond between metal and nonmetal, let us consider the
energy change involve in the formation of sodium chloride. The hole process may
occur in three steps.
1-Ionisation of Atom.
Gaseous sodium atoms
lose an electron and formed cations by absorbing energy equal to ionization
potential.
Na(g)
+ I.P Na+(g)
+ e-
2-Absorption of Electron.
Chlorine atom gains
an electron and converted into anions in this process equal to electron
affinity is released.
Cl(g) +
e- Cl-(g) +
E.A
3-Formation of
Lattice.
The gaseous cations
and anions due to the electrostatic attraction combine together to give stable
ionic crystal.
Na+(g) +
Cl-(g) NaCl(s)
Because the
oppositively charged ions are brought to their position in the crystal lattice
from infinite distance, enough energy is released to make the over all process
energetically favorable, this is known as lattice energy.
Energy of new system
=495-348-788=-641 kj/mole.
The higher the value
lattice energy of the resulting ionic compound the greater the ease of its
formation.
Lattice energy:
“The
energy released when gaseous cation and anion are brought together from
infinite distance to form 1gm mole of solid crystal is called lattice. It is
denoted by “U” and measured kj/mole.”
PROPERTIES OF IONIC COMPOUNDS :
1. Hard solid:
Ionic compounds consist of large no. of oppositively charge ions, which are arrange
in definite pattern at the strong electrostatic forces between ions act in all
direction through the crystal that is why ionic compounds are hard.
2. High melting point due to strong ionic
forces in the crystal, high heat is required to break these forces hence they
possess high melting point.
3. Solubility: Most of the ionic compound
is soluble in water and some other polar solvents because of the strong
electrostatics attractions between the ions and the polar molecules of solvent
causing a release of energy known as “solvation energy” which overcome the high
lattice of ionic compounds in the solution that’s why those are soluble in
water.
4. Electrolytic nature: These are
invariable electrolytes and conduct electricity in molten as well as aqueous
state; this is due to the movement of free ions under the influence of electric
current.
5. An unusual behavior: Some ionic
compounds like sulphate, phosphate, and fluoride of Ca, Sr and Ba are not
soluble even in polar solvent, this is due to their very high value of lattice
energy which is not over come by solvation energy and ions thus do not separate
in free state
COVALENT BOND:
“It is a chemical
bond which is formed by mutual sharing of electrons between two atoms.”
The concept of covalent
bond was introduced by G.N Lewis in 1916 and was later explained by pauling, in
term of wave function.
Covalent bond is
generally represented by short line (-) between the bonded atoms or (:)
electron pair. Covalent bond can be classified into single double or triple
bond on the basis of number of bonded electron pairs. If there is only one
electron pair between the two atoms, this is called single bond(-) similarly if
2 or 3 bonded electron pair are present by (=) or (=) these are called double
or triple bond respectively.
Example:
Cl – Cl, H-H H-Cl
O=O, N =N
PROPERTIES OF
COVALENT COMPOUNDS:
1- They
exist in separate covalent molecule because particles are electrically neutral
and have less attractive forces.
2- These are volatile in nature
and most of them are gases or liquid
3- They posses low boiling point and
melting point.
4- They are usually insoluble in water and
soluble in organic solvent.
IONIC CHARACTER
OF COVALENT BOND::
When a covalent bond
exists between two non identical atom the bonded electron pair will be
attracted more towards high electronegative atom thus one of its end is
relatively negative and other end is relatively positive; in this way a
negative and positive pole appears on the molecules this is called ionic
character of covalent bond or polarization of covalent bond.
In HCl, the bonded
electron pair id distorted due to the high E.N of Cl atom and probability of
finding the electrons near Cl is greater, hence chloride is slightly negative
and hydrogen is slightly positive.
The covalent bond in
HCl is called partially ionic bond or polarized ionic bond or polarized
covalent bond.
The ionic character
of a covalent molecule depends upon the difference in E.N. of the bonded atom.
HF is more polarized
and ionic due to big difference in EN of H and F atoms.
POLAR COVALENT
BOND:
“It is a covalent
bond which exists, between non identical atoms and is based on the distortion
in shared pair of electron between bonded atoms”.
In a covalent bond
between two unlike atoms, the shared electrons pair will be attracted more
towards high electronegative atom. This permanent displacement of electron
paired towards one atom in a covalent bond. It will develop a fraction of negative
charged (-δ) on one atom and a fraction of positive charge (+δ) on another
atom.
The molecule AB has
some ionic character and is called polar molecule and such type of bond is
called as polar polarized covalent bond.
The extent of ionic
character of polar covalent bond depends on the difference of bonded atoms for
e.g. HF is more polar than HCl because the electron cloud of HF molecule is
shifted towards F atom to a greater extent.
A polar covalent bond
is more stable and stronger due to the polarization of ionic character on the
molecule, which makes the bond distance, and short pulls the atoms closer. Thus
high bond energy is needed to break the bond.
The presence of
partial ionic character affects the physical properties of molecules thus
boiling point, melting point, solubility and density increases.
NON-POLAR BONDS:
“A
covalent bond which exists between two identical atoms and the electron density
of the shared atoms is equally distributed to around the two nuclei is called
non polar or non polarized or true covalent bond”
When a covalent bond
exists between two similar atoms A and A, the electron will equally be shared
between the two atoms hence bond will have no ionic character.
e.g. H2 , Cl2 , O2 &
N2
A non-polar bond is
relatively week and unstable due to the
long bond distance and less value of bond energy. Non-polar compound are
generally insoluble in water and have low B.P.
The extent of ionic
character of a polar covalent bond depends on the difference of EN of bonded
atoms.
Reason: Why polar bond
is more stronger than non polar?
A polar covalent bond
is much stronger and stable due to the ionic character or polarization of
molecule. The polarity decreases the bond distance and pulls the atoms closer.
Thus high bond energy is required for bond breaking. Non-polar bond on the
other hand is comparatively week because of non-polarization of molecules and
greater bond distance.
HCl is a polar
molecule and its bond dissociation energy is 431 Kj/mole therefore it is more
stronger than Cl2.
Reason: Bond energy
of “HF” is very high.
Partial ionic
character of HF molecule shortens its bond length and due to the high EN value
of fluorine, the electronic cloud is greatly shifted towards fluorine. Thus the
bond distance of HF would be 0.92 ºA less than the expected bond distance (1.01
A) and hence very high energy is required to break it.
BOND ENERGY :
“ The energy required
to break a bond between two atoms in a diatomic molecule is known as bond
energy, it might be taken as energy released in the formation of a bond from
free atoms and measured in Kj/mole”
Bond energy may be
exothermic and endothermic depending upon bond formation or breaking
respectively.
FACTORS
INFLUENCING BOND ENERGY:
1. POLARITY OF MOLECULES:
The presence of ionic character on the
molecule shortens the bond length and atoms are more strongly bonded together,
therefore energy needed to break the bond would be high.
2. BOND LENGTH:
The
distance between two nuclei in a diatomic molecule is called bond length.
Shorter the bond length more firmly is the atoms held and stronger will be the
bond. That is why bond energy will be high.
3. BOND ODER :
Bond energy increases with the
increased order of bond.
DIPOLE MOMENT :
“The quantitative
measurement of concentration of a molecule is known as dipole moment or it is
the tendency of a molecule to orient in an electric field”
The dipole moment
measures the concentration of positive and negative charges in different part
of the molecule and is equal to the product of ionic charge and distance
between the center of positive and negative charges.
Here q = charge on molecule
d = distance between the center of
positive and negative charges.
REPRESENTATION:
Dipole
moment is represented by (→) along with (-) and the direction of arrow is
towards high electronegative atom in the molecule.
MEASUREMENTS:
Dipole
moment is expressed in Debye after the name of introducer but in S.I system the
unit of dipole moment is C.m(coulomb meter).
The relation between debye and C.m is given below
1
Debye = 10-18 esu X cm = 3.335 x 10-30 sm
SIGNIFICANCE:
Dipole
moment is a measurement of degree of polarity of the molecule greater the value
of dipole moment, more polar will be the molecule. does by knowing the value of
dipole moment, one can predict.
i) The strength and stability of bond .
ii) Its melting and boiling point.
Iii) Its solubility in water.
iv) The geometry of molecule i.e it is
linear or angular.
1-DIPOLE MOMENT OF DIATOMIC MOLECULE:
The dipole moment of
homo diatomic molecule is zero because of unavailability of ionic character in
the molecule.
Cl-Cl H-H
(U=0) (U=0)
The hetreodiatomic
molecules posses dipole moment and its value depends upon extent of
polarization of molecule.
2-DIPOLE MOMENT OF POLYATOMIC MOLECULE.
For polyatomic
molecules dipole moment does not only depend up on the polarity of its bond but
it also depends up on the geometry molecule.
Molecule of CO2
is linear and the bond moment of each C= 0 bond is opposite and equal which
cancels out the effect of each other making CO2 molecule and non
polar and its dipole moment is zero.
Similarly molecule of
CS2 is linear and has zero dipole moment.
H2O is
angular molecule the vector some of bond moment of two H---O bonds is equal but
not in opposite direction and it is polar molecule having a specific dipole
moment.
Molecule of CCl4
has symmetrical structure .the four C-Cl bond are polar but vector sum of dipole
moment of all these are cancelled to each other gives a zero dipole moment due
to the symmetrical structure of molecule.
CO-ORDINATE COVALENT BOND:
This type of chemical
bond was suggested by sidwick and defines as “A covalent bond in which the shared
pair of electron is donated by one atom is called coordinate covalent bond”
In this covalent bond both the electrons are
supplied entirely by one atom .it is a less equitable mode of partnership in
which the contribution is one sided.
REASON OF COORDINATES BOND FORMATION :
Element of group VA, VIA and VIIA remain
have lone pair of electrons after utilizing their valences in the covalent
bond. These lone pair electrons can form a new bond with anther atom having
empty orbital, this is as coordinate bond.
REPRESENTATION:
The dative bond is
represented by (→) and its direction is towards electron accepting group.
It may also be
represented by short line (-) but with the inclusion of positive charge (+) for
electron donor and negative charge (-) for electron accepter.
CHARACTERISTATICS OF COORDINATE COMPOUND
Coordinate
compounds exhibit characterstatics similar to covalent compounds.
1. They do not ionize in water and are
poor conductors of electricity.
2. They are very sparingly soluble in
water but dissolve in organic solvents.
3 Since
a coordinate linkage is semi-polar, melting and boiling point are higher
than those of purely covalent compounds
but lower than ionic compounds.
Example of coordinate compounds
1. Ammoiumion(NH4+):
In ammonia molecule,
the central atom linked to three H+ atoms and yet N has an unshared pair electrons.
the H+ ion furnished by an acid has no electron to contribute and chain accept
a pair of electrons loaned by N atom. Thus NH3 donates
its unshared electrons to H+ forming ammonium ion.
2. Hydronium ion ( H3O+):
The oxygen atom in
water molecule is attached to two atoms by two covalent bonds. There are still
two unshaired pairs of electrons with the O atom. O atom donates one of these
pairs of electron to H+ ion and the hydronium ion is thus formed.
3. Nitromethane( CH3NO2):
The Lewis structure of nitromethane
is shown below.here the N atom has five valence electons, three of which are
used in forming a covalent bond with C atom and two covalent bonds will O atom.
The N atom is still left with two unshared electrons which are denoted to
another O atom.
SIGMA BOND:
“A covalent bond which is formed by head to
head overlapping of atomic orbital is called as sigma bond”
It is generally
established between “S—S”,”S—Px”and Px—Px atomic orbital. sigma bond formation is
based on parallel or linear overlapping of atomic orbital, therefore bond
strength should be maximum and it needs high energy to break a sigma bond.
However the strength of b/w S—S, S—Px and Px—Px are not exactly same.
The S—S overlap is
not so effective due to its spherical charge distribution. P-orbital has
directional charge distribution and longer lobes which cause more effective and
deep overlapping causing short bond length. Thus S—S sigma bond is relatively
weaker than s-p and p-p. The relative bond strength is given as.
Pi BOND:
“A
covalent bond which is formed by lateral or side overlapping of half filled P-
atomic orbital is called as Pi bond”
The overlapping of atomic orbital takes place
perpendicular to inter nuclear axis. In the formation of Pi bond only Py and Pz
orbital take part through side way overlapping, the extent of overlapping is
small and bond formed is weaker.
The sideway
overlapping gives two molecular orbital, Pi bonding and Pi antibonding M.O.
These Pi bonding Nd anti bonding M.O have two regions of electron density below
and above the orbital plane.
VALENCE
BOND THEORY (V.B.T.):
This theory was
proposed by Heitler and London
This theory gives us
a clear explanation about bond length, bond energy and the strength of covalent
molecules. Main postulates of this are given below.
1- A covalent bond is formed by the linear
overlapping of half filled atomic orbital ` in
which electron pair is in opposite spin.
2-
The pairing of electrons in the molecule should satisfy the Paul’s exclusion
principle and the two electrons would have different values of spin quantum
number.
3.
The electron pair may be localized by the two nuclei. The strength of bond,
bond length and bond energy depend upon the extent of overlapping. Deeply
overlapped orbital form relatively stronger bond.
MOLECULAR
ORBITAL THEORY:
This
theory was proposed by Hund and Huckle in 1930, it explains the bond order and
magnetic property of covalent molecule. It consists of following postulates.
1. The
linear combination of atomic orbital gives two type of molecular orbital called
as bonding and anti bonding molecular orbital.
2. Bonding
molecular orbital has low energy (high stability) and anti bonding molecular
orbital has high energy (low stability) with atomic orbital.
3. Electrons in molecular orbital are
multicentered delocalized.
Consider the molecule of H2
molecule.
HYBRIDIZATION:
The
hypothetical process of mixing of different atomic orbital to produce the same
number of equivalent orbital
HAVING SAME SHAPE and energy is known as hybridization,
the orbital so formed are called hybrid orbital”
The
concept of hybridization was introduced by pauling. The type of hybridization
depends upon the number of mixing orbital i.e.SP3,SP2,SP,dSP2,d2SP3
etc.
1- SP3 – HYBRIDIZATION:
It is a mixing of one
s-orbital and three p-orbital to produce four sp3 hybrids orbital is known as
sp3 or tetrahedral hybridization.
Each
sp3 hybrid orbital possesses the character of s and p in the ratio
of 1:3 these are directed at the corner of regular tetrahedron with an angle of
1090 to each other.
EXAMPLE : FORMATION OF METHANE
(CH4):
The
electronic configuration of carbon is given below.
C(z=6) =1s2,2s1,2px1,2py1.
The
2s and three 2p orbital of carbon mixed together to get a set of four equivalent
sp3 hybrid orbital which are located at the corner of regular tetrahedron and
each sp3 orbital of carbon over laps with s orbital of hydrogen from four sigma
bonds.
Other molecules which
show sp3 hybridization are CCl4, SiCl4,SnCl4
etc.
2-
SP2 –
HYBRIDIZATION:
The
mixing of one s and two p atomic orbital to produce three sp2 hybrid
orbital is referred to as sp2 or trigonal hybridization.
OR
These
are the set of three hybrid orbital, which arise from the appropriate
combination of one s, and two p orbital.
These
sp2 orbital are coplanar and directed towards the corners of equilateral with
angle of 120º. Each sp2 hybrid orbital has character of S and P in
the ratio of 1:2 sp2 hybrids orbital is identical in shape.
Example:
Formation of ethane (C2H4)
Each carbon in ethene undergoes sp2
hybridization which is coplanar overlap with each other. at an angle of 120º.
Two-sp2 orbital of each carbon overlap with two S orbital while the
other sp2 orbital
The unhybrid Pz orbital of the two-carbon atom
overlap above and below the plane to form π bond.
Boron trifluoride:
It is also an example of
sp2 hybridization. Boron utilizes its 2s,2px and 2py
orbital for the formation of hybrid orbital. These three hybrids orbital overlap with three p orbital from
three different fluorine atoms to form three B—F bonds at an angle of 120º from
each other.
Others examples of
molecules showing sp2 hybridization are C6H6 CO2
HCN etc
3- SP—HYBRIDIZATION
The
mixing of one S and one P atomic orbital is called SP or diagonal
hybridization. The hybrids SP-orbital are collinear at an angle of 180º which
provide a maximum separation. These SP orbital have character of S and P in the
ratio of 1:1.
One
S orbital can combine with one P orbital on the same atom to form two new and
completely equivalent orbital called sp hybrid orbital.
Example:
Formation of ethyne (C2H2)
 |
Each carbon in ethyne undergoes SP
hybridization, which are collinear at an angle of 180º. One sp1 orbital of each
carbon overlap with one s orbital of hydrogen while the other sp orbital overlaps
with each other.
The unhybridized Py and Pz
orbital of the two carbon atoms overlap above and below the plane to form two π
bonds.
ELECTRON
PAIR REPULSION THEORY:
This
theory explains about the geometry of simple covalent molecules and the ions of
non transitional elements. It is introduced by Sidgewick and Powell in
1940.it is based on the repulsion of electron pairs in the valence shell of
central atom in a molecule.
Main
postulates of this theory are given below.
i) The
central atom in a covalent molecule may have two types of electron pairs, the
bond pairs, and lone pairs of electron. These are called as active set of
electron pairs.
ii) These
bond and loan pair of electrons exert repulsive forces to each other try to be as far apart as possible,
hence they orient themselves in space in such a manner that forces of repulsion
between them is minimized.
iii) The
force of repulsion between two bond pair and loan pair is not the same. The order of repulsion is as
follows.
In case of molecule with double or triple bond, the π electron
pairs are not considered to be involved in the repulsion and hence called as
“inactive set” of electron.
iv) The
shape of molecule depends upon total number of active set of electron pair
around the central atom.
Saturday, December 10, 2011
Saturday, December 3, 2011
Numerical of General Gas Equation And Gas Laws
Hand out #4.1.2
Q. 1Draw the plot from following data
|
Pressure (atm)
|
0.2
|
0.25
|
0.40
|
0.60
|
0.80
|
1.0
|
|
Volume (dm3)
|
112
|
89.2
|
56.25
|
37.40
|
28.1
|
22.4
|
(a)volume against pressure (b)volume
against inverse of pressure (1/p)
Q.2 weather balloon has a volume of 175 dm3 when
filled with hydrogen at pressure of 1.00 atm. Calculate the volume of the balloon
where it rise to a height of 2000 m ‘where the atmospheric pressure is 0.800atm
.Assume that the temperature is constant.
Q.3 What is the volume of given mass of hydrogen at a
pressure of 2.50 atm , if it is volume
is 3.15 dm3 at 1.00 atm
Q.4 A sample of oxygen has a volume of 880 ml and pressure
of 740 torr .What addition pressure is required to reduce the volume to 440ml
Hand out # 4.2.1
Q. 1Draw the
plot Volume and Absolute
temperature from following data
|
Temperature (K)
|
135
|
200
|
270
|
395
|
450
|
540
|
|
Volume (dm3)
|
250
|
372
|
500
|
731
|
838
|
1000
|
Q.2 A sample of helium of gas has volume of 520 cm3
at 373k . Calculate the temperature at which the volume will become 260 cm3
at constant pressure .
Q.3 A mass of Neon occupies 200cm3 at 100oC
.Find its volume at 0oC the pressure remain constant .
Q.4 Anesthetic gas is normally given a patients when the
room temperature is 20 oC and the patient s body temperature is 37o C. What would this temperature change do to 1600ml
of gas at constant pressure and mass remain
constant.
Q.5 What will be the volume at 450K of a gas which occupies
200cm3 at 300K the pressure remaining constant throughout.
Q.6 A sample of oxygen gas occupies 250 cm3at
300K.What volumes it will occupy at 35oC if there is no change in pressure.
Hand out 4.4.1
Q.1 What is the final volume of one mole of nitrogen
initially at S.T.P. If it is subjected to pressure of 2 atm and heated to a
temperature of 546 K
Q.2 7.0 gram of a gas at 300K and one atmospheric
pressure occupies a volume of 4.1 dm3.What is molecular mass of gas
.
Q.3 10.0 gram of oxygen gas are introduced in a vessel of 5
dm3 capacity at 27oC.Calculate pressure of the gas in atmospheric
pressure in the container.
Q.4 Two gas bulbs of the same size are mantainated at same temperature .bulb “A “contain Carbon
dioxide and bulb “B” Contain an equal mass of ethane .
(a)What is the ratio of the number of molecules in the
bulbs?
(b) What is the ratio of the pressures in the bulbs?
Q.5 A sample of nitrogen gas occupies a volume of 1.0 dm3
at pressure of 0.5 atm at 40oC .Calculate the pressure if the gas
compressed to 0.225 cm3 at -6oC.
Thursday, December 1, 2011
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