Notes For All Chapters – General Science Class 7
Elements, Compounds and Mixtures
1. Introduction
- Everything around us is made up of matter.
- Matter can exist in three states: solid, liquid, and gas.
- Matter is made up of elements, compounds, and mixtures.
2. What is Matter?
- Matter is anything that has mass and occupies space.
- It is made up of tiny particles called atoms.
Three States of Matter
| State | Example | Properties |
|---|---|---|
| Solid | Ice, Wood | Fixed shape and volume |
| Liquid | Water, Milk | No fixed shape but fixed volume |
| Gas | Air, Oxygen | No fixed shape or volume |
3. Elements
- An element is a pure substance made of only one type of atom.
- It cannot be broken down into simpler substances.
Examples of Elements
| Metals | Non-Metals | Metalloids |
|---|---|---|
| Iron (Fe), Gold (Au), Silver (Ag) | Oxygen (O), Nitrogen (N), Sulfur (S) | Silicon (Si), Arsenic (As), Boron (B) |
4. Compounds
- A compound is a substance made of two or more elements chemically combined.
- It has new properties different from its original elements.
- Compounds cannot be separated by physical methods.
Examples of Compounds
| Compound | Elements Present | Formula |
|---|---|---|
| Water | Hydrogen + Oxygen | H₂O |
| Carbon Dioxide | Carbon + Oxygen | CO₂ |
| Salt | Sodium + Chlorine | NaCl |
5. Mixtures
- A mixture is made up of two or more substances mixed together without a chemical reaction.
- The substances in a mixture retain their original properties and can be separated easily.
Types of Mixtures
| Type | Definition | Example |
|---|---|---|
| Homogeneous Mixture | A mixture where substances are evenly mixed | Sugar in water, Air |
| Heterogeneous Mixture | A mixture where substances are not evenly mixed | Sand and water, Oil and water |
6. Differences Between Elements, Compounds, and Mixtures
| Feature | Element | Compound | Mixture |
|---|---|---|---|
| Composition | Made of only one type of atom | Made of two or more elements chemically combined | Made of two or more substances physically mixed |
| Separation | Cannot be broken down | Cannot be separated by physical methods | Can be separated easily |
| Properties | Same as the original atoms | Different from the original elements | Retains the properties of its substances |
| Examples | Oxygen, Gold, Iron | Water, Carbon dioxide, Salt | Air, Sand and water, Sugar in water |
7. Methods of Separating Mixtures
- Mixtures can be separated using physical methods.
| Method | Use | Example |
|---|---|---|
| Filtration | Separating solid from liquid | Tea leaves from tea |
| Evaporation | Removing liquid to get solid | Salt from seawater |
| Distillation | Separating two liquids | Purifying water |
| Centrifugation | Separating lighter particles from liquid | Butter from buttermilk |
| Chromatography | Separating colors in ink | Ink separation |
| Separating Funnel | Separating two liquids that do not mix | Oil and water |
8. Rusting of Iron (Corrosion)
✔ Rusting happens when iron reacts with water and oxygen, forming a brownish substance called rust.
✔ Rusting makes iron weak and brittle.
How to Prevent Rusting?
✔ Painting → Covers iron and prevents contact with air and water.
✔ Galvanization → Coating iron with zinc to stop rusting.
✔ Oiling and Greasing → Protects metal surfaces from moisture.
9. Importance of Alloys
- An alloy is a mixture of two or more metals to make them stronger and more useful.
Examples of Alloys
| Alloy | Metals Used | Uses |
|---|---|---|
| Steel | Iron + Carbon | Buildings, Tools |
| Brass | Copper + Zinc | Musical Instruments |
| Bronze | Copper + Tin | Statues, Medals |
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