Matter In Our Surroundings Class 9 Science Short Notes
Introduction
- Matter is the material that makes up everything in the universe, including air, food, stones, clouds, stars, plants, animals, water, and sand.
- All matter occupies space and has mass.
- Early Indian philosophers classified matter into five basic elements - air, earth, fire, sky, and water. Everything, living or non-living, was believed to be made up of these five elements.
- Ancient Greek philosophers also similarly classify matter.
- Modern scientists have two classes of classification of matter: one on the basis of physical nature, and another based upon chemical nature.
Physical Nature Of Matter
Matter consists of tiny, discrete pieces of matter called atoms and molecules. These molecular or atomic units are too small to be seen with the naked eye. The physical and chemical properties of matter are due to the formation, motion, and interaction of such tiny particles which form all the matter in the universe.
Properties of Particles of Matter
1. PARTICLES OF MATTER HAVE SPACE BETWEEN THEM.
The particles of matter, including atoms and molecules, do not occupy the whole volume of the substance. Instead, there are tiny spaces or voids between individual particles. This particle-like characteristic of matter with spaces between it is the very basic concept explaining the numerous physical properties of the substances.
2. PARTICLES OF MATTER ARE ALWAYS IN MOTION.
The particles that compose matter are constantly, randomly in motion, even in solids in which the atoms and molecules have been packed quite tightly.
3. PARTICLES OF MATTER ATTRACT EACH OTHER.
The particles that constitute matter are attracted to each other through a number of intermolecular forces. These include such forces as the van der Waals forces, hydrogen bonding and so on.
States of Matter
Solid State
The particles (atoms or molecules) are closely packed and highly arranged in a solid state of matter in a well-ordered pattern. The attraction between the particles of a solid holds them to their positions as rigid objects which can't easily move around and be compressed in one direction since their inter particle distances are strong, so liquids and gases tend to have very few inter particles. The distance is too much.
Liquid State
- The particles (atoms or molecules) in a liquid are closely packed but not in a fixed, ordered arrangement.
- Liquids can flow and take the shape of the container they are in, as the particles have enough energy to move past one another.
- Liquids have a definite volume but no definite shape, as the particles are not fixed in a rigid structure.
- Liquids can be compressed to some extent.
Gaseous State
In the gas state of matter, the atoms or molecules move freely and very randomly in any direction at fast speeds because particles are very spread out. Between the particles, the attractive forces are very weak, allowing for free movement so that they would fill the container completely.
This means that gases have no specific shape, nor a definite volume, and expand to fill the available space. Gases also have a high compressive strength because the large spaces between them help compress them together. Compressibility:
Change of State Of Matter
It refers to the transition of a substance from one state of matter to another, whether it is a solid, liquid, or gas. This transition occurs due to changes in energy and arrangement among the particles forming the substance.
Matter Can Change its State. Water exists in three forms of matter:
• As ice, in the solid form
• As water, in the liquid form
• As water vapour, in the gaseous form
Effect Of Temperature
1. Melting : This is the condition where an increase in temperature melts a solid: the particles possess increased kinetic energy, thus vibrates rapidly. The particles easily overcome the attraction forces holding the particles together thus melting and taking the shape of a liquid.
2. Melting point: The lowest temperature at which a solid is melted and forms a liquid under atmospheric pressure is known as melting point. Melting point thus gives the intensity of the interparticle attractive forces.
3. Latent heat of fusion: The melting process in a solid does not raise the temperature; however, the melting of the solid absorbs latent heat of fusion that is utilized to overcome the intermolecular forces.
4. Boiling: If the temperature of a liquid increases further, a stage is attained where the particles gain energy enough to fully surpass the attractive forces and can enter the gaseous state with the term boiling.
5.Boiling point: The temperature at which a liquid starts boiling at atmospheric pressure is called the boiling point.
6. Latent heat of vaporization: The heat energy absorbed by a liquid during the boiling process, without causing an increment in its temperature, is called the latent heat of vaporization.
7. Temperature and state change: Increased temperature causes a substance to go from solid to liquid, and from liquid to gas, overcoming the intermolecular attractive forces.
EFFECT OF CHANGE OF PRESSURE
- Gases can be liquefied by increasing pressure and lowering temperature.
- Solid CO2 (dry ice) goes directly from solid to gas without melting, as its phase diagram is unique.
Evaporation
- This phenomenon of a liquid changing into vapor at any temperature, without reaching the boiling point, is called evaporation.
- Change of state does not always require heating or changing pressure. There are cases where liquids can change to vapor without reaching the boiling point.
Examples from everyday life:
Water left uncovered slowly changes into vapor.
Wet clothes dry up as the water in them evaporates.
In liquids, particles at the surface have higher kinetic energy and thus can break loose from the forces of intermolecular attraction; they directly pass into the vapour state.