28:0:0 STRUCTURE OF CRYSTALS:
Solids are divided into two classes which are:
The basic difference between crystals and amorphous is the arrangement of the atoms or molecules in the solids.
Crystals:
A crystal is a piece of solid matter in which the atoms or molecules or ions are arranged in a regular repeating pattern or lattice. Crystals are small particles that make up a crystalline substance. We can also say that crystals are small particles of a crystalline solid which grow out from the solution of a solid when the solid is cooled to freezing point.
When crystals are formed, they grow gradually, touch one another and join to each other. There is high degree of order of particles within the crystals.
Some crystals do not exist as single crystals. When solution of sodium chloride ( NaCl ) is evaporated, flat surface crystals whose edges intersect are formed.
Crystallization:
Crystallization is the formation of crystal of a solid from the solution of the solid when the solution is cooled to its freezing point.
Lattice:
À lattice or crystal lattice is the repeated three dimensional arrangement of particles in a crystal.
The principal features that distiquish solids from liquids is the high degree of regularity in the arrangement of the molecules of the solids and liquids. Particles in liquids are scattered and disorganized because they move about. In gas, the molecules are very very scattered and disorganized more than in liquids.
Structure of simple crystal:
A simple crystal consist of large numbers of building block called unit cells. The unit cells are stacked or packed up and downs, side by side, in all directions to build the entire lattice.
Types of unit cells crystals:
Crystals are named based on where the ions, atoms or molecules are placed.
In a simple cubic lattice crystal, the atoms or ions or molecules are placed side by side, up and down like building blocks until the crystal is formed.
Examples of simple cubic lattice crystals:
In sodium chloride crystal, the atoms of sodium and chlorine are placed alternately in the cube in each of the three dimensions. Each atom within the solid has six immediate neighbors.
Image of sodium chloride crystal:
2. Face centered cubic crystal lattice:
In a face centered cubic crystal lattice, the unit cells are placed at the center of each face of the solid and a unit cell at each of the corners.
Examples of face centered cubic crystal lattice:
Image of face centered cubic crystal lattice
In body centered cubic crystal lattice, the unit cell has identical particles at each corner and one particle at the centre of the cell. Each atom has eight immediate neighboring atoms. The crystal pattern are not seen by human eye. It can only be revealed by X ray diffraction.
Examples of body centered cubic crystal lattice:
Non Crystalline or Amorphous Substances:
Amorphous substances do not have regular shapes because the atoms are not regularly arranged. They do not have any form. They are more like liquids than solids. Amorphous solids usually consist of long, chainline molecules that are intertwined like strands of earthworm.
Examples of amorphous substance:
Glass and plastics are examples of amorphous substances.
Cooling curve for crystalline solids:
The cooling curve for crystalline solid is as shown below.
Curve here:
Explanation of the cooling curve for crystalline solid:
Heating Curve for Crystalline Solid:
The heating curve for crystalline solid is as shown below.
Explanation of heating curve for crystalline solid:
Cooling Curve for Amorphous Solid / substance:
The cooling curve for amorphous substance is as shown below.
Explanation of cooling curve for amorphous substance:
Exercise:
*Differentiate between crystalline solid and amorphous substance. Name three examples of each.
*Name three types of crystal structure that you were taught and name three examples of each.
*With diagram, explain the structure of sodium chloride.
*Explain the following terms: I) crystal (ii) crystallization (iii) Amorphous substance.
*Differentiate between cubic crystal and body centered crystal.
FLUIDS AT REST AND IN MOTION:
Both liquids and gases are able to flow because their molecules are more free to move about. For the reason, liquids and gases are called fluids. Liquids and gases have no rigid shape and they respond to forces in a very different way than solids.
Effect of Surface Tension:
Surface Tension:
Surface tension is the force that act along the surface of a liquid and cause the liquid surface to behave as a stretched elastic skin.
Molecular Explanation of Surface Tension:
Surface tension is due to the intermolecular force of attraction of molecules of the liquid. Consider a liquid in a container. Molecules of liquid anywhere in the liquid experience equally amount of molecular attraction by the neighbouring molecules and therefore have zero resultant force of attraction.
Molecules of liquid at the surface of the liquid only experience molecular force of attraction from molecules of liquid below the liquid surface. This force pulls the molecules of liquid at the surface from below at right angle to the surface, tend to shrink the liquid surface, reduce the surface area of the liquid and strain the liquid surface. This make the liquid surface to behave like elastic skin.
Application of The Effect of Surface Tension:
Effect of surface tension is used to produce umbrellas, raincoats and tents. The materials are treated with oil based substances which prevent water from wetting the material.
It is difficult to wash oily plates or dirty cloths with only water. This is so because the oil or dirt repel the water and does not allow the water to wet the plate or cloth for effective washing. Addition of soaps or detergents weakens or brake the surface tension of the water and enable it to float away the particles of oil or dirt from the plate or dirty cloth.
Detergents contain some chemical which can combine dirt and oil and make the soluble in water.
Reduction of Surface Tension:
Surface tension of a, liquid can be reduced by the following ways:
Capillarity or Capillary Action:
Capillarity or capillary action is the ability or tendency of a liquid to rise or fall in a narrow tube or capillarity tube. The narrower the tube, the stronger the capillarity.
Factors that bring about Capillarity:
The two forces that bring about capillarity are the cohesion force and the adhesion force.
Cohesion force:
Cohesion force is the force of attraction between molecules of the same substances. That is force of attraction between molecules of water and water or force of attraction between molecules of iron and iron. Etc.
Adhesion force:
Adhesion force is the force of attraction between molecules of different substances. That is force of attraction between molecules of water and molecules of glass or force of attraction between molecules of glass and molecules of wood. Etc.
Demonstration of Capillarity:
If a capillarity tube is inserted in water, water rises up the capillarity tube. The married the tube, the higher the water will rise. The wider the tube, the lesser the night of water rise. This can be seen in the figure below.
Reason That Water Wet Glass:
Water wet Glass because the adhesion force between water molecules and glass molecules is stronger than the cohesion force between water molecules.
If a capillarity tube is inserted into mercury, the mercury level in the tube will fall. The wider the tube, the more the mercury level will fall.
Diagram here:
Reason Why Mercury Does Not Wet Glass:
When mercury is poured on to a surface, the mercury does not wet the surface rather the mercury will form ball
Mercury does not wet glass because the cohesion force of Mercury molecules is stronger than the adhesion force between Mercury molecules and glass molecules.
Application of Capillarity:
The action of capillarity is applied in the following:
Friction in Fluid:
It is easy to pour water into and out of a container than, honey, oil, glycerine and other thick liquids. Also, if a stone is dropped into water, the stone falls faster through the liquid and take short time to reach the bottom of the container. If the same stone is dropped into oil, glycerine or any other thick liquid, the stone will fall slowly through the liquid and will take longer time to fall to the bottom of the container. From the two above explanation, it is the friction force between the molecules of the liquid that determined the speed of the stone through the different liquid. In water, the frictional force between the molecules of the water is low hence the stone fall faster through the liquid and take shorter time to reach the bottom. But in oil, the frictional force between the molecules of the oil is grate or large, and it holds the molecules of the oil closely together. This make the oil to be thick. Because of high frictional force between molecules of oil and thickness of the oil, the stone fell slowly through the oil and take longer time to reach the bottom of the container.
Viscosity:
Viscosity is the internal friction force that exist between layers / molecules of a liquid or gas.
High Viscous Fluid:
High viscous fluids are those fluid which pour slowly.
Examples of High Viscous Fluids:
Oil, glycerine, cyrup, mud.
Low Viscous Fluids:
Low viscous fluids are those fluids which pour out easily.
Examples of Low Viscous Fluids:
Water, kerosene, petrol, diesel, etc
Explanation of Terminal Velocity / speed of object falling through viscous fluid:
When a stone is dropped into a viscous fluid, the stone falls through the viscous fluid. As the stone falls through the liquid, the stone accelerates as its velocity increases from zero to maximum value and remain constant for the remaining time that the stone falls through the liquid. This constant velocity is called terminal velocity.
Definition Terminal Velocity / speed of object falling through viscous fluid:
Terminal velocity is the constant velocity or speed of an object that is falling through viscous fluid.
Graph of Terminal Velocity:
Forces that Act on An Object falling through viscous fluid:
Three forces act on any object that falls through viscous fluid. The forces are as follows:
Equation of motion of stone falling through viscous fluid:
Force = mass * acceleration
The effective force that is acting on the stone is obtained by subtracting all the upward forces from the downward force.
Therefore,
effective force that moves the stone down the liquid = W – V – U
Substitution: W – V – U = m*a
W is weight of the stone; V is viscous force of liquid; U is upthrust of liquid on the stone; m is mass of the stone; a is acceleration of the stone as it falls through the liquid.
As the stone falls, the viscous force V increases as the speed of the stone increases. At maximum speed, the viscous force is equal to the weight of the stone. At this point, the stone then moves with constant velocity and its acceleration becomes zero.
Therefore, the above equation now become,
W – V – U = ma . W – V – U = m * 0 W – V – U = 0
Or,
V = W - U
Note: any object that is released from a particular height attains a terminal velocity before it hits the ground.
Similarities Between Viscosity and Friction:
Difference Between Viscous force and Friction Force:
Application of Viscosity:
Viscostatic Fluids:
Viscostatic fluids are fluids whose viscosity increases with in crease in temperature..
Examples of Viscostatic Fluid:
Grease
Exercises:
Solids are divided into two classes which are:
- Crystalline solids or crystals
- Non- crystalline solids or amorphous solids
The basic difference between crystals and amorphous is the arrangement of the atoms or molecules in the solids.
Crystals:
A crystal is a piece of solid matter in which the atoms or molecules or ions are arranged in a regular repeating pattern or lattice. Crystals are small particles that make up a crystalline substance. We can also say that crystals are small particles of a crystalline solid which grow out from the solution of a solid when the solid is cooled to freezing point.
When crystals are formed, they grow gradually, touch one another and join to each other. There is high degree of order of particles within the crystals.
Some crystals do not exist as single crystals. When solution of sodium chloride ( NaCl ) is evaporated, flat surface crystals whose edges intersect are formed.
Crystallization:
Crystallization is the formation of crystal of a solid from the solution of the solid when the solution is cooled to its freezing point.
Lattice:
À lattice or crystal lattice is the repeated three dimensional arrangement of particles in a crystal.
The principal features that distiquish solids from liquids is the high degree of regularity in the arrangement of the molecules of the solids and liquids. Particles in liquids are scattered and disorganized because they move about. In gas, the molecules are very very scattered and disorganized more than in liquids.
Structure of simple crystal:
A simple crystal consist of large numbers of building block called unit cells. The unit cells are stacked or packed up and downs, side by side, in all directions to build the entire lattice.
Types of unit cells crystals:
Crystals are named based on where the ions, atoms or molecules are placed.
- Simple Cubic Lattice:
In a simple cubic lattice crystal, the atoms or ions or molecules are placed side by side, up and down like building blocks until the crystal is formed.
Examples of simple cubic lattice crystals:
- Sodium chloride ( NaCl ):
In sodium chloride crystal, the atoms of sodium and chlorine are placed alternately in the cube in each of the three dimensions. Each atom within the solid has six immediate neighbors.
Image of sodium chloride crystal:
2. Face centered cubic crystal lattice:
In a face centered cubic crystal lattice, the unit cells are placed at the center of each face of the solid and a unit cell at each of the corners.
Examples of face centered cubic crystal lattice:
- Zinc Sulphide ( ZnS ),
- copper,
- silver,
- aluminium
- lead etc
Image of face centered cubic crystal lattice
- Body centered cubic crystal lattice:
In body centered cubic crystal lattice, the unit cell has identical particles at each corner and one particle at the centre of the cell. Each atom has eight immediate neighboring atoms. The crystal pattern are not seen by human eye. It can only be revealed by X ray diffraction.
Examples of body centered cubic crystal lattice:
- Crystal of chromium, iron and platinum salts.
Non Crystalline or Amorphous Substances:
Amorphous substances do not have regular shapes because the atoms are not regularly arranged. They do not have any form. They are more like liquids than solids. Amorphous solids usually consist of long, chainline molecules that are intertwined like strands of earthworm.
Examples of amorphous substance:
Glass and plastics are examples of amorphous substances.
Cooling curve for crystalline solids:
The cooling curve for crystalline solid is as shown below.
Curve here:
Explanation of the cooling curve for crystalline solid:
Heating Curve for Crystalline Solid:
The heating curve for crystalline solid is as shown below.
Explanation of heating curve for crystalline solid:
Cooling Curve for Amorphous Solid / substance:
The cooling curve for amorphous substance is as shown below.
Explanation of cooling curve for amorphous substance:
Exercise:
*Differentiate between crystalline solid and amorphous substance. Name three examples of each.
*Name three types of crystal structure that you were taught and name three examples of each.
*With diagram, explain the structure of sodium chloride.
*Explain the following terms: I) crystal (ii) crystallization (iii) Amorphous substance.
*Differentiate between cubic crystal and body centered crystal.
FLUIDS AT REST AND IN MOTION:
Both liquids and gases are able to flow because their molecules are more free to move about. For the reason, liquids and gases are called fluids. Liquids and gases have no rigid shape and they respond to forces in a very different way than solids.
Effect of Surface Tension:
- Ants walk on water surface
- Dry plant leaf float on water surface
- Formation of balloon or bag by drop of water forming slowly on the mouth of a water tap. Water gradually fill the balloon. The elastic bag support the weight of the water until the spherical drop of water falls.
- Floatation of needle on water surface: Place a needle carefully on a filter paper. Place the filter paper gently on the water surface. The needle will float when the filter paper is soaks and sinks.
Surface Tension:
Surface tension is the force that act along the surface of a liquid and cause the liquid surface to behave as a stretched elastic skin.
Molecular Explanation of Surface Tension:
Surface tension is due to the intermolecular force of attraction of molecules of the liquid. Consider a liquid in a container. Molecules of liquid anywhere in the liquid experience equally amount of molecular attraction by the neighbouring molecules and therefore have zero resultant force of attraction.
Molecules of liquid at the surface of the liquid only experience molecular force of attraction from molecules of liquid below the liquid surface. This force pulls the molecules of liquid at the surface from below at right angle to the surface, tend to shrink the liquid surface, reduce the surface area of the liquid and strain the liquid surface. This make the liquid surface to behave like elastic skin.
Application of The Effect of Surface Tension:
- Production of Waterproof Materials:
Effect of surface tension is used to produce umbrellas, raincoats and tents. The materials are treated with oil based substances which prevent water from wetting the material.
- Cleansing Action of Soaps and Detergents:
It is difficult to wash oily plates or dirty cloths with only water. This is so because the oil or dirt repel the water and does not allow the water to wet the plate or cloth for effective washing. Addition of soaps or detergents weakens or brake the surface tension of the water and enable it to float away the particles of oil or dirt from the plate or dirty cloth.
Detergents contain some chemical which can combine dirt and oil and make the soluble in water.
Reduction of Surface Tension:
Surface tension of a, liquid can be reduced by the following ways:
- By addition of soaps or detergent to the water.
- By increasing the temperature of the water or heating the water.
- By addition of alcohol, camphor.
Capillarity or Capillary Action:
Capillarity or capillary action is the ability or tendency of a liquid to rise or fall in a narrow tube or capillarity tube. The narrower the tube, the stronger the capillarity.
Factors that bring about Capillarity:
The two forces that bring about capillarity are the cohesion force and the adhesion force.
Cohesion force:
Cohesion force is the force of attraction between molecules of the same substances. That is force of attraction between molecules of water and water or force of attraction between molecules of iron and iron. Etc.
Adhesion force:
Adhesion force is the force of attraction between molecules of different substances. That is force of attraction between molecules of water and molecules of glass or force of attraction between molecules of glass and molecules of wood. Etc.
Demonstration of Capillarity:
- Capillarity of Water:
If a capillarity tube is inserted in water, water rises up the capillarity tube. The married the tube, the higher the water will rise. The wider the tube, the lesser the night of water rise. This can be seen in the figure below.
Reason That Water Wet Glass:
Water wet Glass because the adhesion force between water molecules and glass molecules is stronger than the cohesion force between water molecules.
- Capillarity of Mercury:
If a capillarity tube is inserted into mercury, the mercury level in the tube will fall. The wider the tube, the more the mercury level will fall.
Diagram here:
Reason Why Mercury Does Not Wet Glass:
When mercury is poured on to a surface, the mercury does not wet the surface rather the mercury will form ball
Mercury does not wet glass because the cohesion force of Mercury molecules is stronger than the adhesion force between Mercury molecules and glass molecules.
Application of Capillarity:
The action of capillarity is applied in the following:
- Blotting paper absorbs ink when soaked in ink.
- Rising of water in the stern of plants
- The rising up of liquid candle wax on the wick of a candle.
- Rising up of kerosene in the with k of a lamp or stove.
Friction in Fluid:
It is easy to pour water into and out of a container than, honey, oil, glycerine and other thick liquids. Also, if a stone is dropped into water, the stone falls faster through the liquid and take short time to reach the bottom of the container. If the same stone is dropped into oil, glycerine or any other thick liquid, the stone will fall slowly through the liquid and will take longer time to fall to the bottom of the container. From the two above explanation, it is the friction force between the molecules of the liquid that determined the speed of the stone through the different liquid. In water, the frictional force between the molecules of the water is low hence the stone fall faster through the liquid and take shorter time to reach the bottom. But in oil, the frictional force between the molecules of the oil is grate or large, and it holds the molecules of the oil closely together. This make the oil to be thick. Because of high frictional force between molecules of oil and thickness of the oil, the stone fell slowly through the oil and take longer time to reach the bottom of the container.
Viscosity:
Viscosity is the internal friction force that exist between layers / molecules of a liquid or gas.
High Viscous Fluid:
High viscous fluids are those fluid which pour slowly.
Examples of High Viscous Fluids:
Oil, glycerine, cyrup, mud.
Low Viscous Fluids:
Low viscous fluids are those fluids which pour out easily.
Examples of Low Viscous Fluids:
Water, kerosene, petrol, diesel, etc
Explanation of Terminal Velocity / speed of object falling through viscous fluid:
When a stone is dropped into a viscous fluid, the stone falls through the viscous fluid. As the stone falls through the liquid, the stone accelerates as its velocity increases from zero to maximum value and remain constant for the remaining time that the stone falls through the liquid. This constant velocity is called terminal velocity.
Definition Terminal Velocity / speed of object falling through viscous fluid:
Terminal velocity is the constant velocity or speed of an object that is falling through viscous fluid.
Graph of Terminal Velocity:
Forces that Act on An Object falling through viscous fluid:
Three forces act on any object that falls through viscous fluid. The forces are as follows:
- The weight ( W = mg ), of the object which act downward and move the object down through the liquid
- The upthrust U, of the liquid on the stone which act upward and oppose the downward motion of the stone
- Viscous force of the liquid which act upward and oppose the downward motion of the stone.
Equation of motion of stone falling through viscous fluid:
Force = mass * acceleration
The effective force that is acting on the stone is obtained by subtracting all the upward forces from the downward force.
Therefore,
effective force that moves the stone down the liquid = W – V – U
Substitution: W – V – U = m*a
W is weight of the stone; V is viscous force of liquid; U is upthrust of liquid on the stone; m is mass of the stone; a is acceleration of the stone as it falls through the liquid.
As the stone falls, the viscous force V increases as the speed of the stone increases. At maximum speed, the viscous force is equal to the weight of the stone. At this point, the stone then moves with constant velocity and its acceleration becomes zero.
Therefore, the above equation now become,
W – V – U = ma . W – V – U = m * 0 W – V – U = 0
Or,
V = W - U
Note: any object that is released from a particular height attains a terminal velocity before it hits the ground.
Similarities Between Viscosity and Friction:
- The two of them oppose relative motion between two surfaces.
- The two of them depend on the nature of the materials in contact.
Difference Between Viscous force and Friction Force:
- Friction force does not depend on the area of surfaces in contact while viscous force depends on the area of surfaces in contact.
- Friction force depends on the normal reaction, while viscosity does not.
- Friction force occurs in solid while viscosity occurs in liquids and gas or fluids.
- Friction force does not depend on the relative velocities between the two layers in contact while viscosity depends on the relative velocities of the two layers in contact
Application of Viscosity:
- The idea of viscosity enable the use of oil, grease, and air as lubricant. It help to prevent the two surfaces from rubbing together
- Viscosity of air makes the Bob of a swinging pendulum to stop
Viscostatic Fluids:
Viscostatic fluids are fluids whose viscosity increases with in crease in temperature..
Examples of Viscostatic Fluid:
Grease
Exercises:
- The action of blotting paper on ink is caused by ....
- What is the meniscus of water in a capillarity tube?
- Tension three areas in which surface tension is important
- With the aid of diagram, explain the three forces that act on object falling through viscous fluid
- State the equation of object falling through viscous fluid with a terminal velocity.
- Differentiate between force of cohesion and adhesion
- What is the meniscus of mercury in a capillarity tube?
- Why does water wet glass and mercury does not?
- Sketch and explain the graph of terminal velocity
- What is surface tension? Explain its areas of applications.
- Explain surface tension in terms of intermolecular forces.
- Why does a needle float on clean water but sinks when detergent is added.
- Explain the difference in meniscus of water and mercury.
- Describe a simple experiment to demonstrate the surface tension of a liquid.
- Explain two methods of reducing the surface tension of water.
Well done concept. Really appreciate this top-notch, well structured piece.
ReplyDeleteI will need more topics on physics
ReplyDeleteI am happy to find this post Very useful for me, as it contains lot of information. I Always prefer to read The Quality and glad I found this thing in you post. Thanks healing crystals
ReplyDelete