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Chapter-13-solids and liquids

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					Chapter -13                             Liquids and Solids

Review Gases, liquids and solids: Some generalizations, page 378.

Distinguish between different types of forces that exist in
liquids and solids.

Interionic forces: is the strongest of all the forces that exist
between cations and anions that binds them together to form the
crystal lattice of solid ionic compounds. Ionic compounds have
high melting points due to the strong electrostatic attraction
between ions of opposite charges. The greater the strength of
Interionic forces, the higher the melting point of ionic compounds.

Intramolecular forces are the forces that exist between atoms
within a molecule or compound due to covalent bonding.

Intermolecular forces or Van der Waals forces: exist between
molecules. This force is weaker than intramolecular forces and
used to determine the physical properties of molecular substances.

DIPOLE FORCES: If there is a substantial difference in electro
negativity between atoms that make up molecular compounds
such as HCl that contain covalent bonds, due to development of
partial + or –ve charges, charge separation occurs that leads to the
formation of Dipoles.

When molecules with dipole are brought together, the + ve end of
one molecule attracts the –ve end of another molecule .these forces
are called dipole forces.

Hydrogen Bonds: are strong intermolecular forces that exist
between polar molecules that have H atoms covalently bonded to a
more electronegative F/O/N atom of molecule. Hydrogen bonding
accounts for the unusually high boiling points for water, HF and
NH3.

London /Dispersive forces: The motion of electrons in non-polar
molecules produces momentary dipoles that results in an attractive
force that acts between the electron rich one end of molecule and
the electron poor end of the next molecule. The transient attractive
Forces between nonpolar molecules are called London or
dispersive forces. London forces become significant in larger
nonpolar molecules. The strength of dispersive force decreases as
follows: I > Br > Cl > F.

The Liquid State:

The viscosity of liquid is related to the shape of molecules of
liquid. Liquids with low viscosity flow readily as they are made of
small , symmetrical molecules with weak intermolecular forces.2
types of intermolecular forces accounting for high viscosity of
liquids are 1) London dispersion forces (present in larger nonpolar
molecules) and hydrogen bonds present in small unsymmetrical
molecules.

Viscosity decreases with increasing temperature.

Surface Tension: is the force of attraction that causes the surface
of liquid to contract and form a bead or spherical drop. Liquids
with strong intermolecular forces have higher surface tension than
those with weak intermolecular forces.

Chemicals that reduce surface tension of water are called
surfactants found in laundry detergents.

The wetting action is defined as ability of liquid to spread evenly
over a surface as a thin film.
Vaporization is a process by which molecules of liquid break away
to enter into a gaseous phase.

The reverse process of vaporization in which the vapor of liquid is
converted back into liquid is called condensation.


Evaporation is a process in which a liquid with low boiling point
(volatile liquid) is converted from liquid phase to gaseous phase.

In a closed system, when rate of evaporation of liquid is equal to
the rate of condensation of liquid, dynamic equilibrium is
achieved.

The temperature at which liquid boils when the vapor pressure of
liquid becomes equal to the atmospheric pressure (1atm /760 torr)
is referred as the normal Boiling point of liquid. Boiling points
are used to identify the given unknown liquids.

Distillation: is a procedure used to resolve liquid mixtures on the
basis of difference in their boiling points. Boil the liquid mixture in
round bottom flask to produce vapors. When vapor temperature
corresponds to its boiling point, the separated liquid distills out in
pure form. Simple distillation is made up of one vaporization and
one condensation step.

Heat is absorbed from surroundings to vaporize a liquid. The
quantity of heat required to vaporize 1 mol of a liquid at constant
pressure and temperature is called molar heat of vaporization.

Example 13.4, pg: 389.

The Solid State: The molecules of solid are closely and tightly
packed in definite array and pattern that defines the crystal lattice
and three dimensional structure of solid. The degree of freedom of
motion for the molecules of solid is very much restricted. The
molecules of solid vibrate or oscillate from their almost fixed
positions. As temperature increases the vibration of molecules of
solid also increases.

Solids are broadly classified as Crystalline solids and
Noncrystalline solids.

Noncrystalline solids: are irregularly shaped and structured
amorphous solids. Molecules are not packed in definite order and
hence crystal lattice is absent. Amorphous solids do not exhibit
sharp melting points and soften gradually when heated.

Crystalline Solids: The molecules of solid are closely and tightly
packed in definite array and pattern that defines the crystal lattice
and three dimensional structure of solid. The three types of crystal
lattice found in crystalline solids are shown in fig 13.13, pg. 390.
They are simple cubic, body centered cubic and face centered
cubic arrangement.
Cr, Mn, Fe and Alkali metals have body centered cubic
arrangement in their crystal lattice.

Some ionic compounds like NaCl, KCl and CaO have face-
centered cubic arrangement in their crystal lattice.

Classification of solids on the basis of bonding found in them
Review the information in detail given in table 13.4 on page 391.

Ionic solids have ions in each lattice point. (Hard, high melting, low vapor
pressure, soluble in water)

       Molecular solids have individual, discrete covalent molecules at the
lattice points. (Soft, low melting, high vapor pressure, insoluble in water)
Covalent network/Macromolecular solids: contain atoms at the
lattice points that are connected by covalent bonds leading to
extensive network distributed throughout the molecule.
These solids are extremely hard and nonvolatile, have extremely
high melting points. Examples of such solids are tungsten carbide,
Quartz, Silicon carbide and SiO2.

When an element is capable of existing in 2 or more different
physical forms in the same state, they are referred as Allotropes.
The allotropes of carbon are diamond, graphite, nanotube
(synthetic allotrope) which also happens to be covalent network
solids. The carbon atoms are tetrahedral arranged in diamond
connected by covalent bonds (fig 13.14/392). In Graphite the
carbon atoms form hexagonal framework in each plane. The
different planes are stacked in layers which slide over one another
(fig. 13.15/ 393).

Metallic solids: refer to pg: 224/ fig. 8.9.
Metallic solid has three dimensional arrays of positive ions that
remain fixed in the crystal lattice and the loosely held valence
electrons cruise freely throughout the crystal like a fluid making
the metallic solids as good conductors of heat and electricity.

Melting point, Freezing point and Heating curve of water.

The temperature at which solid and liquid exist in dynamic
equilibrium is called melting point of solid

The temperature at which liquid and solid are in dynamic
equilibrium is called Freezing point.

Molar heat of Fusion: The amount of heat required to convert 1
mol of a solid to a liquid at its melting point is called Molar heat of
fusion.
Molar heat of vaporization: The amount of heat required to
convert 1 mol of a liquid into gas at its boiling point is called
Molar heat of Vaporization.

Study the figure 13.18, page v395 which displays the heating curve
for water.

Heat of fusion is less than heat of vaporization because less energy
is required ( slope of solid in fig 13.18) to disrupt the molecules of
Crystal lattice (solid) to allow the molecules to move around
freely in the liquid state.
The molecules of liquid still experience intermolecular force of
attraction between them. Substantial amount of energy supplied in
the form of heat is required (slope of liquid water in fig 13.18) to
disrupt and overcome the intermolecular force of attraction
experienced between the liquid molecules. This enables the liquid
molecules to escape into gaseous phase.

Review example 13.1, 13.2, 13.4, 13.5and 13.7 discussed in
chapters 13.

From this chapter I will just test you on definitions and on energy
problems similar to 13.5 or 13.7.

HW Assignment
13.2, 13.7, 13.9, 13.11, 13.12, 13.15, 13.53 and 13.65.

Due next Thursday.

				
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