CBSE Class 8 > Class 8 Notes > Science Curiosity - New NCERT > Cheat Sheet: Elements Compounds And Mixtures
Cheat Sheet: Elements Compounds And Mixtures
1. Nature of Matter - Definitions & Classifications
1.1 Definitions
| Term | Definition |
|---|---|
| Matter | Anything that has mass and occupies space |
| Mixture | Two or more substances combined with each substance retaining its own properties and not reacting chemically |
| Component | An individual substance present in a mixture |
| Pure substance | Contains only one kind of matter throughout and cannot be separated by physical processes |
| Element | Pure substance made of only one type of atom |
| Compound | Pure substance formed by chemical combination of two or more elements in a fixed ratio |
| Physical change | Change that alters state without changing the type of substance |
| Non-matter | Entities lacking mass or volume such as light, heat, electricity, thoughts, emotions |
| Alloy | Mixture of two or more metals with distinct combined properties |
| Mineral | Naturally occurring substance found in rocks |
| Air Quality Index (AQI) | Index used to describe air quality |
1.2 Types of Mixtures
| Type | Characteristic |
|---|---|
| Heterogeneous mixture | Non-uniform; components visible and separable by sight or simple methods |
| Homogeneous mixture | Uniform; components not visible separately even under a microscope |
1.3 Types of Pure Substances
| Type | Characteristic |
|---|---|
| Elements | Cannot be broken into simpler substances by chemical means |
| Compounds | Formed in fixed ratios and possess properties different from constituent elements |
1.4 Classification of Elements
| Class | Characteristic |
|---|---|
| Metals | Good conductors; shiny; malleable |
| Non-metals | Poor conductors; brittle |
| Metalloids | Properties intermediate between metals and non-metals |
1.5 Key Facts about Elements
| Fact | Value |
|---|---|
| Total known elements | 118 |
| Elements gaseous at room temperature | 11 |
| Elements liquid at room temperature | Mercury and bromine |
| Solids that melt near 30°C (303 K) | Gallium and caesium |
| Common physical state | Most elements are solids at room temperature |
2. Mixtures, Compounds, and Tests
2.1 Air and Pollutants
| Term | Detail |
|---|---|
| Air | Uniform mixture of gases mainly nitrogen, oxygen, argon, carbon dioxide, and water vapour |
| Pollutants in air | Particulate matter and gases such as carbon monoxide, ozone, NO₂, SO₂ |
| AQI | Air Quality Index describes air quality |
2.2 Tests and Observations
| Test | Observation |
|---|---|
| Lime water preparation | Calcium oxide added to water produces lime water (calcium hydroxide) |
| Lime water reaction | Lime water turns milky on exposure to air due to formation of insoluble calcium carbonate, indicating carbon dioxide |
| Electrolysis of water | Water decomposes into hydrogen and oxygen gases |
| Common gas tests | Hydrogen gives a 'pop' with flame; oxygen makes a glowing flame burn brighter |
2.3 Mixture versus Compound
| Aspect | Comparison |
|---|---|
| Composition | Mixture: component proportions can vary; Compound: elements combined in fixed ratios |
| Properties | Mixture: components retain original properties; Compound: new properties different from constituents |
| Separation | Mixture: separable by physical methods; Compound: requires chemical methods |
3. Minerals, Uses, and Applications
3.1 Minerals
| Term | Detail |
|---|---|
| Mineral definition | Naturally occurring substance found in rocks; most rocks are mixtures of minerals |
| Mineral composition | Minerals are either pure elements or compounds of elements |
| Native minerals | Pure elements occurring in elemental form in nature |
| Compound minerals | Minerals made of two or more elements combined chemically |
3.2 Everyday Presence and Role in Innovation
- Elements, compounds, and mixtures form the basis of everyday materials
- Chemical combinations of elements enable development of medicines and vaccines
- Knowledge of compounds improves fertilizer design and crop production
- Engineers use compounds and mixtures to design stronger materials
- Minerals supply raw materials for buildings, tools, and products
- Common construction materials are often mixtures chosen for combined properties like strength and flexibility
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