Solids, Liquids and Gases Class 5 Notes Science

Molecules and Atoms

•  Anything that takes up space and has mass is referred to as matter. 
•  Matter can be found in three forms: solids, liquids, and gases. 
•  Matter consists of very small particles known as molecules. 
•  A molecule is a tiny piece of a substance that retains all the characteristics of that substance. 
•  Molecules are too small to be seen with the human eye. 
•  The arrangement of molecules varies between different substances. 
•  Molecules can be divided into even smaller units called atoms. 
• Atoms are the smallest parts of matter and cannot be split into smaller pieces. 

Elements and Compounds

• Atoms of the same kind combine to form elements.
• Elements are pure substances that cannot be broken down into simpler substances by chemical means. They are the basic building blocks of matter and are made up of atoms.
• Atoms of different kinds combine to form compounds.
• Compounds are substances made from two or more different elements that are combined together in a specific way. They have their own unique properties that are different from the elements that form them.
• Water is a common example of a compound that is made of two kinds of elements i.e. hydrogen and oxygen. 

Arrangement of Molecules in Matter  

There are three states of matter solid, liquid and gas. Molecules in matter are always moving. They constantly attract each other and keep moving towards each other. All the three states have different arrangements of molecules. 

• Solids: In solids, the molecules are tightly packed. They attract each other with a strong force of attraction. There is no intermolecular space between the molecules so they cannot move. That is why solids have definite shapes and volumes. 
• Liquids: In liquids, the molecules are not as closely packed as in solids. The force of attraction between the molecules is less as compared to that of solids. There is intermolecular space between the particles so that they can move freely. That is why liquids can flow. Liquids have definite volume but no definite shape. 
• Gases: In gases, the molecules are far apart with large intermolecular spaces between them. They can move freely in all directions. So, gases can flow easily and take up all the available space. Gases do not have definite shapes and volumes. 

Solutions and Solubility

• A solution is a mixture formed when a solute dissolves in a solvent. 
• A solute is a substance that gets dissolved in a liquid. 
• A solvent is a liquid that dissolves a solute to create a solution. For example, in a glass of saltwater, water is the solvent because it dissolves the salt.

Solvent + Solute = Solution 

• Some solids dissolve in water. We call them soluble substances.
  For example, sugar, salt, juices. 
• Some solids do not dissolve in water. We call them insoluble substances.
  For example, sand, chalk, tea leaves, and oil.

 Factors affecting Solubility

• Stirring a Solution: Some substances dissolve quickly on stirring.
• Temperature: More sugar can dissolve in hot water than in cold water.

How does a Solution Form?

 1. Solubility of Solids 

• Solid solutes like salt, sugar, etc. dissolve in water to form a solution. 
• Molecules of the solute that are added to the solvent, occupy the space between the molecules of the solvent to form a new liquid, which is called a solution.

2. Solubility of Gases 

• Just like solids, gases also dissolve in water and occupy the gaps in it.
• Fizzy drinks are a solution of the gas carbon dioxide in water. The bubbles that you see in a fizzy drink are of carbon dioxide.
• Water in lakes, ponds, seas, etc., has gases dissolved in them. Fish breathe the oxygen dissolved in water.

3. Solubility of Liquids

• When two liquids can be mixed to form a solution they are called miscible.
  Example: Water and rose syrup are miscible.
• When two liquids cannot be mixed to form a solution they are called immiscible.
  Example: Oil and water are immiscible.

Water is called a universal solvent because it dissolves more substances than any other liquid.
This property is very important for life because it means that wherever water goes, either through the air, through the ground, or through our bodies, it takes along valuable chemicals, minerals, and nutrients dissolved in it.

Change of State 

Matter can change from one state to another on heating or cooling.

Melting 

When ice is kept out of a refrigerator, it melts into water. The process of changing a solid into a liquid on heating is called melting.
When ice is kept in a warm place, the molecules of ice start vibrating faster and become free from the rigid form. They become loosely packed to form water.

Evaporation 

When water is heated, it changes into water vapour. The process of changing of a liquid into a gas on heating is called evaporation. The molecules of water start vibrating faster on heating. They become free and escape into the air as gas. Molecules of a gas move much more freely.

Condensation 

When the steam touches a cold surface, it changes into water. The process of changing a gas into a liquid on cooling is called condensation. When molecules of steam or water vapour touch a cold surface, their movement slows down. They become less free to move and form water. 

Freezing 

When water is kept in a freezer, it changes into ice. The process of changing a liquid into a solid on cooling is called freezing. In cooling water, the molecules slow down and come very close to each other. They pack themselves into a rigid form to make ice.

Expansion and Contraction of Matter 

• When we heat a substance, the molecules start vibrating rapidly. 
• Due to this intermolecular space between the molecules increases and the substance expands. 
• Thus, expansion is the increase in the size of matter on heating. For example, the tight metal lid of a jar can be opened easily by dipping it in hot water. 

• This happens because hot water causes the lid to expand a little and thus it opens out easily. 
• Similarly, electric wires between electric poles hang loose in the summer season. 

• On the other hand, when we cool a substance, the movement of molecules slows down. 
• Due to this intermolecular space between the molecules decreases and the substance contracts. 
• Thus, contraction is the decrease in the size of matter on cooling. For example, electric wires do not hang loose between electric poles in the winter season. 

Physical and Chemical Changes

There is a difference between the physical and chemical changes that take place as matter changes its form. Let's learn about them.

Physical Changes 

A physical change is a temporary change that can be reversed. For example, the melting of ice, evaporation of water, melting of wax and glowing of a bulb are physical changes as they give us back the original substance.

Examples: 

• Boiling, melting, freezing, and shredding
• Melting of butter, ice cream, wax 
• Shredding of paper, clothes, etc 
• Chopping wood

The original material remains the same. These changes are in the state of matter and can be reversed easily.

Chemical Changes

A chemical change is a permanent change that cannot be reversed. For example, burning of paper, burning of matchsticks, cooking of food and formation of curd from milk are chemical changes.

Examples: 

• Burning, cooking, rusting, and rotting 
• Burning wood 
• Souring milk 
• Cooking an egg 
• Heating sugar to form caramel 
• Baking a cake 
• Rusting of iron

We cannot get original things back when a chemical change occurs in them. A chemical change results from a chemical reaction.