Week 6 and 7 – SS1 Third Term Physics Notes

WEEK 6
TOPIC: CRYSTAL STRUCTURE OF MATTER- AMORPHOUS AND
CRYSTALLINE SUBSTANCES.
CONTENT : Crystal Structure

Crystalline and Amorphous Substance

  The term crystal structure is generally used to describe the internal structure of solids. The particles of a solid are orderly arranged in parallel planes. In other words, solid crystals consist of particles arranged in parallel planes. Crystals are built up from simple structural units called unit cells. A unit cell (also called a space lattice) is made up of few atoms, ions or molecules.
There are seven types of unit cells. Each type gives rise to a crystal system. They include cubic, rhombic, monoclinic, triclinic, tetragonal, rhombohedra and hexagonal crystal system. X- ray analysis of crystal shows that three pairs of opposite parallel faces bund the unit cells in all crystal systems, except in hexagonal system. We can draw three imaginary lines between the centres of the opposite parallel faces.
These imaginary lines represent three axes of symmetry. The length of these axes of symmetry and the angles between them determines the system to which a crystal belongs. This is demonstrated using cubic and monoclinic crystal systems.
In a cubic crystal system, the axes of symmetry have equal length and at right angles to each other. This type of crystal system is found in copper, sodium chloride, silver, gold, iron, sodium, potassium etc. however, the type of cubic crystal system found in copper, silver, gold and sodium chloride is different from the type found in sodium, iron and potassium. The former is called face centred cubic, while the later is called body centred cubic. In a monoclinic system, the axes are not equal in length and only two of them are at right angles to each other. These crystal systems are in sugar, washing soda, ferrous sulphate etc.
EVALUATION

1. What is a unit cell?
2. With the aid of diagram, distinguish between cubic crystal system and monoclinic crystal system.

DIFFERENCES BETWEEN CRYSTALLINE AND AMORPHOUS SUBSTANCES
On the basis of internal structure of solid, we can classify a solid as either a crystal substance (e.g. common salt) or an amorphous substance (e.g. glass). The differences between the two substances are:
                                                                                                Crystalline substance Amorphous substances             1. Have a definite internal arrangement Have a haphazard distribution of particles
of particles.
2. Have a cleavage planes along which Do not have cleavage planes
they fracture when struck
3. Meets sharply at a definite temperature Do not meet sharply at a definite
when heated. temperature
4. Regarded as true solid Regarded as super cooled liquids
5. Have a long range order of arrange- Have short range order of arrangement
ment of particles of particles
6. Are efflorescence substance Are not efflorescence substance
EVALUATION

1. Differentiate between crystalline and amorphous substances
2. Define crystal lattice

Reading Assignment : Read more on crystal structure of matter – New school physics (pg99- 101)

WEEKEND ASSIGNMENT
1. crystal structure is generally used to describe (a) the external structure of solids
(b) the internal structure of solids
(c)
the internal structure of liquids
(d) the external structure of liquids
2.
Particles of a solid are orderly arranged in .,……….. planes (a) parallel (b) horizontal (c) vertical (d) none of the above
3. Unit cell is also known as (a) monoclinic system (b) polyclinic system (c)space lattice (d) none of the above
4. ………… substance has a definite internal arrangement of particles (a) Amorphous (b) Crystalline (c) Elastic (d) Atomic
5. ………….. are not efflorescence substance (a) Amorphous (b) Crystalline (c) Elastic (d) Atom
THEORY

1. Differentiate between crystalline and amorphous substances
2. Define crystal lattice

 
WEEK 7
TOPIC: SURFACE TENSION
CONTENT: * Definition of surface tension
* Effect of surface tension
* Application of surface tension
* Reduction of surface tension

 Surface Tension:
(1) Is the property of a liquid to make its surface behave as though it is covered by an
elastic skin.
(2) Is the force per unit length. Y= F/2L
(3) Is the force acting parallel to the surface of the liquid

Effects of Surface Tension
1 Soap bubbles are spherical in shape
2. Water stakers are able to walk on the surface of water
3. Razor blade or needle gently placed on the surface of water floats
4. Spilled mercury on glass surface form spherical droplets

 EVALUATION

1. Define surface tension
2. State the three effects of surface tension

Application of surface tension

1. use in the manufacturing of rain proof or water proof
2. absorption of ink with blotting paper
3. rising of oil in lamp wicks
4. movement of melted wax into the neck of a burning candle

 Reduction of surface tension

1. adding impurities such as detergent/soap, alcohol, oil, camphor, kerosene, grease
2. by heating the liquid.

EVALUATION

1. State three applications of surface tension
2. State two ways of reducing surface tension

Reading Assignment : Read more on surface tension – New school physics (pg102-103)

WEEKEND ASSIGNMENT

1. Define surface tension. State the three effects of surface tension
2. (a)State three applications of surface tension (b)two ways of reducing surface tension