Pure Substances
A pure substance is a material made up of only one kind of particles and has fixed composition and properties.
Types of Pure Substances
-
Elements – Made of only one type of atom.
Examples: Oxygen, Iron -
Compounds – Formed when two or more elements combine chemically in a fixed ratio.
Examples: Water, Carbon Dioxide
Characteristics of Pure Substances
- Have fixed composition
- Have definite melting and boiling points
- Cannot be separated by physical methods
Mixtures
A mixture is formed when two or more substances are mixed together physically without any chemical change.
Types of Mixtures
1. Homogeneous Mixture
A mixture with uniform composition throughout.
Examples:
- Salt solution
- Air
2. Heterogeneous Mixture
A mixture with non-uniform composition.
Examples:
- Sand and water
- Oil and water
Characteristics of Mixtures
- Composition may vary
- Components retain their properties
- Can be separated by physical methods
- Do not have fixed melting or boiling points
Solutions and Their Properties
Solution
A solution is a homogeneous mixture of two or more substances.
- The substance that dissolves is called the solute.
- The substance in which the solute dissolves is called the solvent.
Example: In salt water, salt is the solute and water is the solvent.
Properties of Solutions
1. Homogeneous Nature
A solution has a uniform composition throughout.
2. Very Small Particle Size
The particles of a solution are extremely small and cannot be seen with naked eyes.
3. Particles Do Not Settle Down
The solute particles do not settle at the bottom when left undisturbed.
4. Cannot Be Separated by Filtration
The particles are so small that they pass through filter paper.
5. Transparent in Nature
Most solutions are transparent and allow light to pass through.
6. Stable Mixture
The components of a solution remain mixed uniformly for a long time.
Types of Solutions
1. Solid in Liquid
Example: Salt in water
2. Liquid in Liquid
Example: Alcohol in water
3. Gas in Liquid
Example: Carbon dioxide in water (soft drinks)
Concentration of a Solution
The amount of solute present in a given amount of solvent or solution is called concentration.
Types
- Dilute Solution – Contains less solute
- Concentrated Solution – Contains more solute
Saturated and Unsaturated Solutions
Saturated Solution
A solution in which no more solute can dissolve at a given temperature.
Unsaturated Solution
A solution in which more solute can still dissolve at a given temperature.
Suspensions and Colloids
Suspension
A suspension is a heterogeneous mixture in which insoluble particles are spread throughout the liquid.
Examples
- Muddy water
- Chalk powder in water
Properties of Suspensions
- It is a heterogeneous mixture.
- Particles are large enough to be seen with naked eyes.
- Particles scatter light passing through them.
- Particles settle down when left undisturbed.
- Components can be separated by filtration.
Colloids
A colloid is a heterogeneous mixture in which very small particles are evenly spread throughout another substance.
Examples
- Milk
- Fog
- Smoke
Properties of Colloids
- Colloids appear homogeneous but are actually heterogeneous.
- Particles are very small and cannot be seen easily.
- Particles do not settle down on standing.
- Colloids scatter light due to the Tyndall effect.
- Components cannot be separated by ordinary filtration.
Physical and Chemical Changes
Physical Change
A physical change is a change in which only the physical properties of a substance change, and no new substance is formed.
Characteristics of Physical Changes
- No new substance is formed.
- Usually temporary and reversible.
- Only physical properties like shape, size, or state change.
Examples
- Melting of ice
- Boiling of water
- Cutting paper
Chemical Change
A chemical change is a change in which one or more new substances are formed with different properties.
Characteristics of Chemical Changes
- New substances are formed.
- Usually permanent and irreversible.
- Energy may be released or absorbed.
- Change in color, smell, or temperature may occur.
Examples
- Rusting of iron
- Burning of wood
- Cooking food
Elements and Compounds
Elements
An element is a pure substance made up of only one kind of atom. It cannot be broken down into simpler substances by chemical methods.
Examples of Elements
- Oxygen
- Hydrogen
- Iron
- Gold
Characteristics of Elements
- Made of only one type of atom.
- Pure substances with fixed properties.
- Cannot be separated into simpler substances chemically.
Compounds
A compound is a pure substance formed when two or more elements combine chemically in a fixed ratio.
Examples of Compounds
- Water (Hydrogen + Oxygen)
- Carbon Dioxide
- Common salt (Sodium + Chlorine)
Characteristics of Compounds
- Formed by chemical combination of elements.
- Components are present in fixed proportions.
- Properties are different from the elements that form them.
- Can be broken into elements only by chemical methods.
Types of Elements – Metals, Non-Metals and Metalloids:
Elements are classified into metals, non-metals, and metalloids based on their physical and chemical properties.
1. Metals
Metals are elements that are generally hard, shiny, and good conductors of heat and electricity.
Properties of Metals
- Lustrous (shiny)
- Good conductors of heat and electricity
- Malleable (can be beaten into sheets)
- Ductile (can be drawn into wires)
- Usually hard and strong
Examples: Iron, Copper, Gold, Aluminium , etc.
2. Non-Metals
Non-metals are elements that are generally soft and poor conductors of heat and electricity.
Properties of Non-Metals
- Dull appearance
- Poor conductors of heat and electricity
- Brittle (break easily)
- Not malleable or ductile
Examples
- Oxygen
- Sulfur
- Carbon
3. Metalloids
Metalloids are elements that show properties of both metals and non-metals.
Properties of Metalloids
- Have mixed properties of metals and non-metals
- Semiconductors of electricity
- Usually brittle solids
Examples
- Silicon
- Germanium
- Boron
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