1. Lecture 70 – Lecture 71 – Lecture 72 Liquids and Solids Ozgur Unal
NIS – CHEMISTRY
Lecture 70 – Lecture 71 – Lecture 72
Liquids and Solids
Ozgur Unal

2. Liquids Can take the shape of its container Have a fixed volume
Are much denser than gases
Are considered incompressible, unlike gases
Kinetic-molecular theory can also be applied to liquids.
The particles in a liquid also moves randomly, but this motion is limited to smaller space compared to gases.
The forces of attraction between particles (interparticle forces) play an important role.

3. Liquid Fluidity
Gases and liquids are classified as fluids because they can flow and diffuse.
Liquids usually diffuse more slowly than gases at the asme temperature, because intermolecular attractions interfere with the flow.
Liquids are less fluid than gases.
Example: Water and natural gas in pipes

4. Liquid Viscosity
Viscosity is a measure of the resistance of a liquid to flow.
The particles in a liquid are close enough for attractive forces to slow their movement as they flow past one another.
There are three factors that affect the viscosity of a liquid:
Intermolecular forces
Size and shape of the particles
Temperature

5. Viscosity Attractive forces: In typical liquids, the stronger
the intermolecular attractive
forces, the higher the viscosity.
Particle size and shape:
Recall kinetic energy (KE)  depends on mass and speed
Consider 2 different liquids A and B at the same temperature
If the molecules in A are heavier, then liquid A is more viscous than B.

6. How do you think temperature changes viscosity?
Viscosity decreases with temperature.
Example: The oil in a frying pan
starts flowing easily as you heat it.

7. Surface Tension
How do you think this spider is able to stand on the water?
Do you think intermolecular forces have anything to do with this?

8. Surface Tension
Particles in the midlle of a liquid can be attracted from particles above and below them.
The particles at the surface are attracted by the particles below.
In order to increase the surface area of a liquid, the particles below the surface has to overcome these intermolecular attraction forces.
The energy required to
increase the surface area of
a liquid by a given amount
is called surface tension.

9. Surface Tension
In general, the stronger the attractions between particles, the greater the surface tension.
Water’s high surface tension is what allows the spider to walk on the surface of the pond.
Why do water droplets form a sphere?
Why do we use soaps and detergents in water to remove dirt from dishes and clothes?
Compounds that lower the surface tension of water are called surfactants.

10. Cohesion and Adhesion How can you explain the surface shape
(called meniscus) of this liquid in the container?
Cohesion describes the force of attraction between identical molecules.
Adhesion describes the force of attraction between molecules that are different.
If a cylinder is extremely narrow, a thin film of water will be drawn upward  capillary action

11. Solids In solids, the intermolecular attractive
forces are dominant  particles are tightly
packed and they vibrate at their position.
Fixed volume and shape  not a fluid!
Generally solids have higher density than most liquids.
Incompressible
Some solids become less dense
when they melt  benzene
Some solids become more dense
when they melt  water

12. Crystalline Solids
In most solids, including ice, the molecules in the solid are packed together in a predictable way.
A crystalline solid is a solid whose atoms, ions or molecules are arranged in an orderly, geometric structure.
Check out Figure for the three ways that particles in a crystal lattice can be arranged to form a cube.

13. Crystalline Solids A unit cell is the smallest
arrangement of atoms in a
crystal lattice that has the
same symmetry as the whole
crystal.
The unit cell can be thought
of as a building block whose
shape determines the shape
of the crystal.
Check out Table 12.4 for the
seven categories of crystals
based on shape.

14. Categories of Crystalline Solids
Crystalline solids can be classified into five categories based on:
the types of particles they contain
how those particles are bonded together.
These categories are:
Atomic solids
Molecular solids
Covalent network solids
Ionic solids
Metallic solids
The only atomic solids are noble gases  their properties reflect the weak dispersion forces between the atoms

15. Categories of Crystalline Solids
Molecular solids:
In molecular solids, molecules are held together by dispersion forces, dipole-dipole forces or hydrogen bonds.
Poor conductor of electricity.
Most molecular compounds are not solids at room temperature.
Example: Water
Molecular compounds with
high molar mass are solid at
room temperature.
Example: Sugar

16. Categories of Crystalline Solids
Covalent network solids:
Atoms such as C and Si, which can form
multiple covalent bonds, are able to form
covalent network.
Example: Quartz (contains Si)
Ionic solids:
Each ion in an ionic solid is surrounded
by ions of opposite charge.
The type of ions and the ratio of ions
determine the structure of the lattice and
the shape of the crystal.
Example: Salt

17. Categories of Crystalline Solids
Metallic solids:
Remember that metallic solids consist
of positive metal ions surrounded by a
sea of mobile electrons.
As the mobile electrons increase, the
metal becomes a better conductor, more malleable and ductile.
Amorphous solids:
An amorphous solid is one in which the particles are not arranged in a regular pattern  no crystals
It forms when a molten material cools too
quickly to allow enough time for crystals to form.
Example: Rubber and plastics