Class 10 Science Chapter 1 Notes: Chemical Substances: Nature and Behaviour

Class 10 Science Chapter 1 Notes: Chemical Substances: Nature and Behaviour: This chapter is one of the most crucial parts of Class 10 Science. It deals with the chemical properties, reactions, and behaviors of various substances, which form the foundation for understanding Chemistry. Let’s explore the chapter with detailed one-liners for each concept.

1. Chemical Reactions and Equations

1.1 What is a Chemical Reaction?

A chemical reaction is a process in which substances (reactants) undergo a change to form new substances (products) with different properties. It is represented by chemical equations.

1.2 Characteristics of Chemical Reactions

• Formation of a precipitate: A solid product formed during the reaction.
• Change in color: Indicates a chemical change, e.g., iron rusting.
• Evolution of gas: Bubbles observed in the reaction of acids with carbonates.
• Change in temperature: Exothermic reactions release heat, while endothermic reactions absorb heat.
• Change in state: Substances may change their state, e.g., solid to liquid.

1.3 Types of Chemical Reactions

• Combination Reaction: Two or more substances combine to form one.
• Example: 2H₂ + O₂ → 2H₂O
• Decomposition Reaction: A single compound breaks into two or more products.
• Example: 2HgO → 2Hg + O₂
• Displacement Reaction: A more reactive element replaces a less reactive one.
• Example: Zn + CuSO₄ → ZnSO₄ + Cu
• Double Displacement Reaction: Exchange of ions between two compounds.
• Example: NaCl + AgNO₃ → AgCl + NaNO₃
• Oxidation and Reduction:
• Oxidation: Gain of oxygen or loss of hydrogen.
• Reduction: Gain of hydrogen or loss of oxygen.
• Example: CuO + H₂ → Cu + H₂O

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2. Acids, Bases, and Salts

2.1 Acids

• Substances that release H⁺ ions in an aqueous solution.
• Examples: Hydrochloric acid (HCl), Sulphuric acid (H₂SO₄), Acetic acid (CH₃COOH).
• Properties: Sour taste, turn blue litmus red, and react with metals to release hydrogen gas.

2.2 Bases

• Substances that release OH⁻ ions in an aqueous solution.
• Examples: Sodium hydroxide (NaOH), Potassium hydroxide (KOH), Ammonium hydroxide (NH₄OH).
• Properties: Bitter taste, slippery to touch, turn red litmus blue.

2.3 Indicators

Indicators are substances that change color to identify acids and bases.

• Natural Indicators: Litmus, turmeric, red cabbage.
• Synthetic Indicators: Phenolphthalein, methyl orange.
• Olfactory Indicators: Onion, vanilla.

2.4 Neutralization Reaction

A reaction between an acid and a base to form salt and water.

• Example: NaOH + HCl → NaCl + H₂O

2.5 Salts

Salts are the products of neutralization reactions between acids and bases.

• Common Salts and Uses:
• Sodium chloride (NaCl): Common table salt.
• Baking soda (NaHCO₃): Used in cooking and as an antacid.
• Washing soda (Na₂CO₃): Cleansing agent.

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3. Metals and Non-Metals

3.1 Metals

• Elements that are good conductors of heat and electricity.
• Examples: Iron (Fe), Aluminum (Al).
• Properties:
• Lustrous (shiny appearance).
• Malleable (can be beaten into thin sheets).
• Ductile (can be drawn into wires).
• High tensile strength.

3.2 Non-Metals

• Elements that are poor conductors of heat and electricity.
• Examples: Carbon (C), Sulfur (S).
• Properties:
• Non-lustrous (dull appearance).
• Brittle (break easily).
• Low melting and boiling points.

3.3 Reactivity of Metals

• Reactivity depends on the tendency to lose electrons.
• Reactivity Series:
• Highly reactive: Potassium (K), Sodium (Na).
• Moderate reactive: Zinc (Zn), Iron (Fe).
• Least reactive: Gold (Au), Platinum (Pt).

3.4 Corrosion

• The process where metals react with substances in the environment to form undesirable compounds.
• Example: Rusting of iron (Fe₂O₃ · xH₂O).
• Prevention:
• Painting, galvanization, alloying.

4. Carbon and Its Compounds

4.1 Covalent Bonding

• Carbon forms covalent bonds by sharing electrons.
• Example: Methane (CH₄).

4.2 Allotropes of Carbon

• Diamond: Hard, used in cutting tools.
• Graphite: Conducts electricity, used in lubricants.
• Fullerenes: Spherical molecules of carbon.

4.3 Hydrocarbons

• Compounds containing carbon and hydrogen.
• Types:
• Alkanes: Saturated hydrocarbons (CnH₂n+2).
• Alkenes: Unsaturated hydrocarbons with double bonds (CnH₂n).
• Alkynes: Unsaturated hydrocarbons with triple bonds (CnH₂n-2).

4.4 Functional Groups

• Groups of atoms that determine the chemical properties of compounds.
• Alcohols (-OH): Ethanol (C₂H₅OH).
• Carboxylic acids (-COOH): Acetic acid (CH₃COOH).

5. Periodic Classification of Elements

5.1 Mendeleev’s Periodic Table

• Elements were arranged based on their atomic masses.
• Strength: Helped predict properties of undiscovered elements.
• Limitation: No place for isotopes.

5.2 Modern Periodic Table

• Elements are arranged based on their atomic numbers.
• Trends in the Modern Periodic Table:
• Atomic size: Decreases across a period, increases down a group.
• Metallic character: Decreases across a period, increases down a group.

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Frequently Asked Questions in EXAMS (BOARD & CBSE) from the past five years

Here are some frequently asked questions from the past five years for the chapter “Chemical Substances: Nature and Behaviour” in Class 10 Science:

1. Chemical Reactions and Equations

1. Define a chemical reaction and list its characteristics. (1/2 Marks)
2. Write a balanced chemical equation for the following:
   • The reaction of iron with steam. (2 Marks)
   • The thermal decomposition of calcium carbonate. (2 Marks)
3. Distinguish between displacement and double displacement reactions with examples. (3 Marks)
4. What is oxidation? Give an example. (2 Marks)
5. In the reaction: CuO + H₂ → Cu + H₂O, identify the oxidizing and reducing agents. (1 Mark)

2. Acids, Bases, and Salts

1. What happens when an acid reacts with a metal? Give the equation. (2 Marks)
2. Name a natural indicator and its color change in acidic and basic mediums. (1 Mark)
3. Explain the importance of pH in everyday life with examples. (3 Marks)
4. Write the chemical formula of washing soda. How is it prepared? List one use. (3 Marks)
5. Why does tooth decay occur more easily when the pH of the mouth is lower than 5.5? (2 Marks)

3. Metals and Non-Metals

1. Why are metals good conductors of electricity? (1 Mark)
2. Write the balanced chemical equation for the reaction of sodium with water. (2 Marks)
3. What is corrosion? How can it be prevented? (3 Marks)
4. State the reactivity series. Why is gold found in a free state in nature? (3 Marks)
5. Why is aluminum used to make aircraft bodies? (2 Marks)

4. Carbon and Its Compounds

1. Explain covalent bonding with the example of methane. (3 Marks)
2. Write the IUPAC names of the following compounds:
   • CH₃CH₂OH (Ethanol)
   • CH₃COOH (Acetic acid) (2 Marks)
3. What are hydrocarbons? Differentiate between saturated and unsaturated hydrocarbons with examples. (3 Marks)
4. What are allotropes of carbon? Mention one use of diamond and graphite. (2 Marks)
5. Explain why carbon forms a large number of compounds. (3 Marks)

5. Periodic Classification of Elements

1. State Mendeleev’s periodic law. Mention one limitation of Mendeleev’s periodic table. (2 Marks)
2. Why does atomic size decrease across a period? (2 Marks)
3. Elements X and Y have atomic numbers 11 and 17, respectively. Predict the type of bond they will form and write its formula. (3 Marks)
4. Differentiate between groups and periods in the modern periodic table. (2 Marks)
5. How do the properties of elements vary in a group and across a period? (3 Marks)

5-Mark Questions (Long Answer)

1. Write the reactions involved in the preparation of the following salts and name the type of reaction:
   • Sodium chloride
   • Washing soda
   • Plaster of Paris
2. Describe the modern periodic table. Mention any three trends observed in it.
3. Draw the electron dot structure of methane and explain covalent bonding in it.

These questions will help you understand the types of questions usually asked and the key areas to focus on while preparing for exams. Let me know if you need detailed answers or explanations!

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Conclusion

The chapter ‘Chemical Substances: Nature and Behaviour’ explains the fundamentals of chemical reactions, the behavior of acids, bases, salts, and the unique properties of metals and non-metals. Understanding these concepts thoroughly helps in scoring well in exams and builds a foundation for advanced Chemistry topics.