CLASS 7_ MATTER AND ITS COMPOSITION

This is a simulation showing the motion of particles in different states of matter.

https://phet.colorado.edu/sims/html/states-of-matter-basics/latest/states-of-matter-basics_en.html

SOME  VIDEOS

1.  https://www.youtube.com/watch?v=jmm1J2yI9tk 

2.  IS FIRE A SOLID?

3. https://www.youtube.com/watch?v=ENVKQVIDNLY

4. https://phet.colorado.edu/sims/html/states-of-matter/latest/states-of-matter_en.html


LINK FOR CONCISE CHEMISTRY EXERCISE QUESTIONS

https://www.aplustopper.com/selina-concise-chemistry-class-7-icse-solutions-matter-and-its-composition/

MATTER AND ITS COMPOSITION 

MATTER

Anything that occupies space, has mass and can be perceived by our senses is called     matter.

E.g. water, wood, air etc.

 COMPOSITION OF MATTER

Matter is made up of small particles called atoms, molecules and ions.

 ATOM

An atom is the smallest unit of matter that may or may not exist independently but can take part in a chemical reaction.

 MOLECULE

A molecule is the smallest unit of pure substance that exists independently and exhibits all the properties of that substance.

It can be made up of same type or different type of atoms.

E.g. H₂, Cl₂, H₂O, etc.

A molecule of hydrogen (H₂) is made up of 2 hydrogen atoms.

A molecule of water (H₂O) is made up of 2 hydrogen atoms and 1 oxygen atom.

CHARACTERISTICS OF MATTER (or PARTICLES OF MATTER)

               1.      Particles of matter are very small.

2.      Particles of matter have space between them. The space between the particles of matter are called inter- particle or inter-molecular space.

3.      Particles of matter are in constant random motion.

4.      Particles of matter attract each other. The force of attraction between the particles of matter holds them together and is called inter-molecular force of attraction.

STATES OF MATTER

The physical state of a substance is determined by:

   i. The magnitude of inter-particle force of attraction.

 ii.  The randomness of motion of the particles.

iii. The magnitude of inter-particle space.

Thus matter can exist in any of the three states:  Solid, Liquid and Gas.

 There are two more states of matter i.e. Plasma State and Bose-Einstein Condensate (BEC).

Table 1: Difference between the Three States of Matter

Property	Solid	Liquid	Gas
Shape	Definite	No definite shape	No definite shape
Volume	Definite	Definite	No definite volume
Packing of particles	Very closely packed	Less closely packed	Least closely packed
Free Surface	Any number of free surfaces	One free surface	No free surface
Fluidity	Does not flow	Can Flow	Can Flow
Rigidity	Highly rigid	Less rigid	Not rigid
Intermolecular space	Minimum	More than solids but less than gases	Maximum
Intermolecular force of attraction	Maximum	Less than solids but more than gases	Minimum
Diffusion	Do not undergo diffusion	Show diffusion	Diffuse easily
Compressibility	Incompressible	Negligible	Highly compressible

Fluids: All substances that can flow are called fluids. Liquids and gases are fluids.

INTERCONVERSION OF STATES OF MATTER

The change in state of matter is caused by

1. Change in temperature

2. Change in pressure.

  

Melting or Fusion

The process by which a substance changes from solid state to liquid state on absorbing heat is called melting or fusion.

E.g. Ice changes to water.

Freezing or Solidification

The process by which a substance changes from liquid state to solid state is called freezing or solidification.

E.g. Water changes to ice

Vaporisation

The process of conversion of a substance from its liquid state to its vapour state is called vaporisation.

E.g. Water changes to water vapour

Condensation or Liquefaction

The process of conversion of a substance from its gaseous state to liquid state is called condensation or liquefaction.

Liquefaction of a gas can also be brought about by the application of pressure. Gases have to be cooled to a certain temperature before application of pressure.

E.g. Water vapour condenses to water.

Sublimation

Sublimation is the process by which a substance changes from solid state directly to gaseous state without passing through the intermediate liquid state or vice versa.  

The solid formed by the condensation of vapours of the substance that sublimes on heating is called sublimate.

E.g. of sublimable substances are naphthalene, camphor, iodine, dry ice, ammonium chloride etc.

                        _____________________________________________

Review of Concepts:

1. An ice cube is placed in a closed container. On heating, the ice cube first melts and the water then boils to form steam. Which of the following statements is true?

(a) The physical appearance of the water is different at every stage of change.

(b) The mass of water is greatest for the ice cube and least for the steam

EXERCISE

1.      1.      Define matter.

2.      Write your observations and conclusions for the following:

               i. When few marbles are put in a glass half filled with water.

Ans.: Observation: The water level rises.

 Conclusion: The marbles occupy space. Thus matter occupies space.

             ii. Ice kept at room temperature.

Ans.: Observation: The ice melts and changes to liquid state.

Conclusion: Solid changes to liquid state by absorbing heat energy.

3.      Why liquids and gases are called fluids?

Ans.: Liquids and gases can flow. So they are called fluids.

4.      Give reasons:

                 i. When a stone is dipped in a glass containing some water, the level of water rises but when a spoon of sugar is added to it and stirred, the water level does not rise.

Ans.: The stone occupies space so the level of water rises. The sugar particles are small and occupies the intermolecular space in water. So the water level does not rise.

               ii. A drop of ink added to water in a glass turns the whole water blue.

Ans.: The water and ink particles are in continuous random motion. The particles of ink diffuse in water and spreads all over.