TOPIC 6: STRUCTURE AND PROPERTIES OF MATTER
Structure of Matter
State of matter is defined in terms of phase transitions, which indicate changes in structure and properties. Solids, liquids, and gases are all made up of microscopic particles. The behavior of these particles varies in the three phases.
The Concept of Matter
Matter is anything, such as a solid, liquid, or gas, that has weight (mass) and occupies space. For anything to occupy space, it must have volume.
The Particulate Nature of Matter
Matter is made up of tiny particles called atoms or molecules. Examples of substances made up of atoms include gold, copper, argon, and silver; those made up of molecules include oxygen, water, and ammonia.
- In solids, strong attractive forces hold molecules together so that they are not free to move but can only vibrate about their mean positions.
- In liquids, there are weak forces of attraction between molecules; therefore, the molecules are free to move randomly. The distances between molecules in liquids are larger than in solids.
In gases, the molecules experience very weak forces of attraction and hence are free to move randomly, filling the whole space of the containing vessel. The distances between molecules in gases are comparatively greater than those in solids and liquids, as shown in the figure below.
Demonstration to show the intermolecular space in solids, liquids, and gases.
The Kinetic Theory of Matter
Generally, when solid particles are placed near a heat source, the particles tend to move from hot areas to cold areas. These particles move because they gain energy called kinetic energy.
The kinetic theory of matter attempts to explain how properties of gases like pressure, temperature, and volume remain constant in motion.
There are three main parts of the kinetic theory of matter:
- Matter is made up of tiny invisible particles.
- Matter comes in different sizes.
- The smallest particles of matter can be the fastest.
Therefore, the kinetic theory of matter states: “All matter is composed of small particles” or “Particles of matter are in steady motion and all impacts between the units of matter are completely elastic.”
Three States of Matter
There are three states of matter, namely:
- Solid state
- Liquid state
- Gaseous state
Solid state is the state of matter which includes solid materials, in which the intermolecular forces between molecules are greatest and the distance between molecules is small. Examples of solid state are wood, iron, etc.
Liquid state is one of the states of matter in which the intermolecular forces are low compared to solid state, and there is greater distance between molecules. Examples include water, soda, kerosene, and petroleum.
Gaseous state is the state of matter in which there are no intermolecular forces between molecules; hence molecules are free to move from one place to another. Examples of gases are hydrogen, oxygen, and carbon dioxide.
Difference between Solid, Liquid, and Gaseous States of Matter
| Solid state | Liquid state | Gaseous state |
|---|---|---|
| Concerns solid matter | Concerns liquids/fluids matter | Concerns gases |
| Has high intermolecular forces | Has low intermolecular forces | No intermolecular forces |
| No distance between molecules | There is little distance between molecules | Molecules are far from each other |
| Examples: iron, wood, etc. | Examples: water, soda, kerosene, petrol | Examples: oxygen, hydrogen |
Brownian Movement
According to Robert Brown: Brownian movement refers to the irregular motion of tiny particles suspended in a fluid (liquid or gas). Consider the demonstration below.
Robert Brown, an English botanist, powdered some pollen grains in water and observed that particles floating in the water were darting about.
The irregular motion of tiny particles suspended in a fluid (liquid or gas) is called Brownian movement.
The tiny particles dart about because liquid molecules that are in a state of motion bombard them.
Elasticity
The Concept of Elasticity
When a force is applied to a body, the dimensions of the body are usually altered. If an iron wire is stretched by a small force applied longitudinally, the wire returns to its original shape and size when the force is removed.
Elasticity can be defined as the property of the iron wire by which it recovers its original shape and size on removal of the stretching force.
The Relationship between Tension and Extension of a Loaded Elastic Material
Consider the graph below:
Point A is called the elastic limit. The straight region OA of the graph has a slope K given by the ratio:
K = Tension / Extension
The ratio is called the force constant or coefficient of stiffness of the wire and is expressed in newtons per metre (N/m).
The Application of Elasticity in Real Life
In everyday life, we often engage in activities that involve the application of physics. Here are some applications of elasticity:
- Spring mattress: When you sit or sleep on a spring mattress, your weight compresses the springs. Due to elasticity, the springs stretch and compress repeatedly.
- Springs used as shock absorbers on motorcycles: Springs in suspension systems dampen shocks when a motorcycle travels over uneven surfaces.
- Catapults: Rubber slingshots stretch when pulled and return to their original shape after the force is removed due to elasticity.
Adhesion and Cohesion
The Concept of Adhesion and Cohesion
Matter is made up of molecules that exert forces of attraction. These forces may be either cohesion or adhesion.
- Cohesion is the force of attraction between molecules of the same substance, e.g., water molecules attracting each other.
- Adhesion is the force of attraction between molecules of different substances, e.g., water molecules attracting glass molecules.
Water molecules experience cohesion among themselves, while water molecules and glass molecules experience adhesion.
Definite shapes of solids are due to strong cohesive forces among their molecules.
Shapes and Meniscus of a Liquid
When determining the volume of a liquid in a ring or measuring cylinder, the surface of the liquid forms a meniscus. The volume must be read at the bottom or top of the meniscus depending on the liquid used. For mercury, the top of the meniscus is read.
The formation of a meniscus in a liquid is due to adhesion forces between the liquid and the walls of the container. Adhesion of liquids such as water to the vessel walls causes an upward force on the liquid at the edge.
The meniscus of water curves upwards forming a concave shape. When drops of mercury and water are placed on a glass sheet, water spreads further than mercury because mercury has a higher cohesion force among its particles.
Why Water Wets Glass?
Water wets glass due to adhesion forces between water molecules and glass molecules.
Why Methanol Does Not Wet Glass?
Methanol does not wet glass because of weaker adhesion forces between methanol molecules and glass molecules.
Applications of Adhesion and Cohesion in Daily Life
- To stick two different objects together using adhesive effects of tape or glue.
- Adhesion is used to remove harmful materials such as bacteria from drinking water.
- Cohesion assists in the transport of water in plants and animals by allowing one molecule to pull others along.
- Cohesion helps tissues in plants and animals repair damage.
- Ink sticks on paper because of adhesive forces between the paper and ink.
Surface Tension
The Concept of Surface Tension
Surface tension is the ability of molecules on the surface of a liquid to attract and stick to each other, allowing them to resist an external force. This property enables insects such as water striders and mosquitoes to walk on water. It also allows small objects, even metallic ones like needles and razor blades, to float on the surface of water.
Surface tension results from attractive forces between molecules in a liquid. Molecules below the surface have forces of attraction between neighboring particles. However, molecules at the surface have no neighboring molecules above them, making their attractive force stronger than that of their nearest neighbors on the surface.
When detergent is added to water, objects that previously floated sink because the detergent reduces the surface tension of the water.
Detergents are examples of surfactants. A surfactant is a substance that reduces the surface tension of a liquid.
Note: The term surfactant is an acronym for surface-active agent.
Factors Affecting Surface Tension
- Nature of the liquid
- Contamination or impurities
- Temperature
Applications of Surface Tension
- Extraction of impurities during laboratory processes.
- Surfactants are used to make emulsions of liquids like oil and water.
- Cleaning action of soap.
Applications of Surface Tension in Daily Life
- Extraction of impurities during laboratory processes.
- Surfactants are used to make emulsions of liquids like oil and water.
- Cleaning action of soap.
Capillarity
The Concept of Capillarity
Capillarity is the tendency of a liquid to rise in narrow tubes or to be drawn into small openings such as those between the fibers of a towel. Capillarity can pull a column of liquid upward until the weight of the liquid becomes greater than the surface tension.
In a tube, capillarity depends on the tube’s diameter, but the weight of the water column depends on other factors as well.
The smaller the radius of the tube, the higher the liquid will rise in it. This implies that capillarity height is inversely proportional to the diameter of the tube.
By definition, capillarity is the tendency of liquid to rise in narrow tubes or to be drawn into small openings such as those between the fibers of a towel.
Capillarity action is the ability of a liquid to rise or fall in a narrow tube.
- Capillarity depends on the type of liquid. For example, if you dip a capillary tube in water, the water rises in the tube and above the level of the water in the vessel.
- If the tube is dipped in mercury, the liquid does not rise in the tube. It suffers capillarity depression.
Applications of Capillarity in Daily Life
- Capillarity is essential to plants and animals.
- In plants, it facilitates the transport of water and nutrients from the roots to the leaves where photosynthesis produces the plant’s food. In animals, it assists in the circulation of blood.
- Capillarity promotes the movement of groundwater.
- It is the principle on which paper and fabric towels absorb water.
- Cotton clothing in hot climates uses capillarity action to draw perspiration away from the body.
- In oil or kerosene lamps, capillarity draws the fuel up into the wick where it can be burnt.
- A writing pen splits in the middle so that a fine capillary is formed.
Osmosis
The Concept of Osmosis
Osmosis is defined as the movement of a solvent from a region of low concentration to a region of high concentration through a semi-permeable membrane.
Particles will diffuse through the membrane in an attempt to equalize the concentration on either side. For example, two solutions of different concentration separated by a semi-permeable membrane. The membrane is permeable to the smaller solvent molecules but not to the larger solute molecules. Osmosis stops when the concentration becomes the same on either side of the membrane.
Applications of Osmosis in Daily Life
- Control the movement of water and nutrients in and out of cells.
- Filtration processes.
- Removal of harmful ingredients from drinking water.
- Removing salt from seawater to make it suitable for drinking and other domestic uses.
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