ICSE Class 8 Chemistry Language of Chemistry Notes | PDF Download

Introduction

Are you searching for ICSE Class 8 Chemistry Language of Chemistry Notes PDF Download? This chapter is one of the most important topics in ICSE Class 8 Chemistry because it introduces students to chemical symbols, valency, radicals, formula writing, and chemical equations. These notes will help students understand the basics of chemistry in a simple and easy language.

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Language of Chemistry | ICSE Class 8 Chemistry Notes

Symbol

A symbol is a shorthand notation representing an element (e.g., H for Hydrogen, O for Oxygen).

Need for Symbols

Symbols are used because:

• They make the representation of elements and compounds simpler.
• They help in writing chemical equations easily and clearly.

Rules for Writing Symbols

1. Single Letter Symbols

The symbol is the first letter of the element’s name, written in capital.

Examples:

• Hydrogen → H
• Oxygen → O
• Carbon → C

2. Two-Letter Symbols

If two or more elements start with the same letter, use two letters.
The first letter is capital, the second is small.

Examples:

• Cobalt → Co
• Calcium → Ca
• Chlorine → Cl
• Chromium → Cr

3. Each Symbol Represents One Atom

Examples:

• H represents one atom of hydrogen.
• C represents one atom of carbon.

4. Symbols Derived from Latin or Greek Names

Some symbols come from the Latin or Greek names of elements.

Examples:

• Iron → Ferrum → Fe
• Sodium → Natrium → Na
• Potassium → Kalium → K
• Copper → Cuprum → Cu

Valency

Valency is the combining capacity of an atom of an element or a radical with other atoms to form molecules or compounds.

Examples

• Hydrogen Chloride (HCl):
  One atom of chlorine combines with one atom of hydrogen.
  Valency of chlorine = 1
• Water (H₂O):
  One atom of oxygen combines two atoms of hydrogen.
  Valency of oxygen = 2
• Ammonia (NH₃):
  One atom of nitrogen combines with three atoms of hydrogen.
  Valency of nitrogen = 3
• Methane (CH₄):
  One atom of carbon combines with four atoms of hydrogen.
  Valency of carbon = 4

Trend in Valency

• The valency of elements increases from 1 to 4 and then decreases back to 1.

• Elements like Helium, Neon, and Argon have a valency of 0, as their outermost electron shell is complete — they are inert gases.

Modern Concept of Valency

Valency can also be defined as:
The number of electrons lost, gained, or shared by an atom during a chemical reaction or when forming compounds.

Example 1: Sodium Chloride (NaCl)

• Sodium atom loses one electron → forms Na⁺ (cation).
• Chlorine atom gains one electron → forms Cl⁻ (anion).
• Hence, both have a valency of 1.

Example 2: Hydrogen Chloride (HCl)

• Hydrogen shares one electron with chlorine.
• Both have a valency of 1.

Name, Symbol, and Valency of the some Important Elements

Variable Valency

Some elements can show more than one valency.
This happens because they can lose different numbers of electrons in different compounds.

Examples of Metals with Variable Valency

Naming Rule

• Lower valency: ends with -ous (e.g., Ferrous → Fe²⁺)

• Higher valency: ends with -ic (e.g., Ferric → Fe³⁺)

Radicals / Ions

• A radical is an atom or a group of atoms that behaves as a single unit with a positive or negative charge.
• Radicals are also called ions.

Types of Radicals

(i) Basic Radicals

• Have a positive charge.
• Also called cations.
• All metallic ions and ammonium (NH₄⁺) are basic radicals.

(ii) Acid Radicals

• Have a negative charge.
• Also called anions.
• Mostly non-metallic ions or groups with negative charge.

Valency and Symbols of Some Common Positive Radicals

Valency and Symbol of Common Negative Radicals

Naming an Ion or a Radical

1. For Positive Ions (Cations)

Derived from the parent element name.

Example: Na⁺ → Sodium ion,

Cu⁺ → Cuprous ion

2. For Negative Ions (Anions):

Derived by replacing the last few letters of the element’s name with the suffix “-ide”.

Example: Cl⁻ → Chloride ion,
O²⁻ → Oxide ion

3. For Polyatomic Ions:

Names often end with –ate, –ite, or –ide depending on oxygen content.

Examples:

• SO₄²⁻ → Sulphate ion
• SO₃²⁻ → Sulphite ion
• OH⁻ → Hydroxide ion

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Molecular Formula of Compounds

• A molecular formula represents the symbols and number of atoms of each element in a molecule.

• It shows:
  • The types of atoms present.
  • The number of each atom in the compound.

• Examples
  • Sulphur dioxide (SO₂):
    One atom of sulphur + two atoms of oxygen → SO₂
  • Water (H₂O):
    Two atoms of hydrogen + one atom of oxygen → H₂O

To Write a Molecular or Chemical Formula

To write a chemical formula, the following are needed:

1. Symbols of elements or radicals
2. Valencies (combining capacities) of the elements/radicals

The criss-cross method is used to write the formula.

Molecular formulae of some common compound

Naming rules for simple compounds

• Rule 1 : metal + non-metal
  The name of metal is written first, then the name of non-metal is written with ‘-ide’ ending.
  Example:
  CaO – Calcium Oxide
• Rule 2 : non-metal + non-metal
  The number of atoms of each element is generally indicated in the name by ‘di’, ‘tri’, ‘tetra’, ‘Penta’ etc.
  Example:
  • N₂O₅ – dinitrogen pentoxide
  • PCl₃ – Phosphorus trichloride
    (prefix mono is not used)
• Rule 3: If the first element of a molecular compound is Hydrogen, the number of its atom is not written.
  Example:
  H₂S – Hydrogen Sulphide

Important points

• Always write metal (positive radical) first, followed by the non-metal (negative radical).
• Reduce the valencies to their lowest ratio when possible.
• Use brackets for polyatomic radicals if more than one unit is required.
  Example: Ca(NO₃)₂ → Calcium nitrate.
• The subscript in a chemical formula represents the number of atoms of that element.

Significance of Molecular / Chemical Formula

1. Represents one molecule of a compound.
2. Shows the elements or ions present in the compound.
3. Indicates the number and ratio of each kind of atom or ion in one molecule.
4. Helps calculate the molecular mass of a compound, if the atomic masses of its elements are known.

Example: Sulphur Dioxide (SO₂)

• Molecular formula: SO₂
• Elements present: Sulphur (S) and Oxygen (O)
• Composition: 1 atom of Sulphur + 2 atoms of Oxygen
• Molecular mass of SO₂ = 32 + (2 × 16) = 64 amu

Atomic Mass

The mass of an atom is called its atomic mass.
Because atoms are extremely small, their masses are measured using a standard reference atom.

Atomic Mass Unit (amu):

• Defined as 1/12th of the mass of one atom of carbon-12 isotope.
• The atomic mass of an element is a number that shows how heavy its atom is compared to 1 amu.
• Symbol: amu (atomic mass unit)

Examples of Atomic Masses (First 20 Elements)

Chemical Equations

A chemical equation is the symbolic representation of a chemical reaction using symbols and formulae of the substances involved.

Key Terms:

• Reactants: Substances that react (present on the left-hand side).
• Products: Substances formed as a result of the reaction (present on the right-hand side).

Example:

• Burning of coal in air

• Word equation:
  Carbon + Oxygen → Carbon dioxide
• Symbolic equation:
  C + O₂ → CO₂
  Here,
  Reactants: Carbon, Oxygen
  Product: Carbon dioxide

Steps Involved in Writing a Chemical Equation

1. Write the symbols or formulae of the reactants on the left-hand side, with a plus (+) sign between them if more than one.
2. Write the symbols or formulae of the products on the right-hand side, with a plus (+) sign between them if more than one.
3. Put an arrow (→) between the reactants and products.
   The arrow points from reactants to products.
4. Represent the reactants and products by their correct formulae.
5. The equation should be balanced, i.e., the number of atoms of each element on both sides must be equal.

Examples of Chemical Reactions

1. Reaction of Lead Monoxide with Carbon: PbO + C → Pb + CO

2. Reaction between Iron and Sulphur: Fe + S → FeS

3. Reaction between Carbon Dioxide and Water: CO₂ + H₂O → H₂CO₃

4. Reaction between Calcium Oxide and Water: CaO + H₂O → Ca(OH)₂

Word Equation

A word equation shows the names of the reactants and products involved in a chemical reaction.
Example:
Magnesium + Oxygen → Magnesium Oxide

Skeletal Chemical Equation

If the number of atoms of each element in the reactants is not equal to the number of atoms of each element in the products, the equation is called a Skeletal Chemical Equation.
It is also known as an Unbalanced Chemical Equation.
Example:
Mg + O₂ → MgO

Balanced Chemical Equation

A balanced chemical equation is one in which the number of atoms of each element on the reactant side is equal to the number of atoms of the same element on the product side.
Example:
2Mg + O₂ → 2MgO

Need for Balancing a Chemical Equation

• A chemical equation must be balanced to satisfy the Law of Conservation of Mass, i.e., the number of atoms of each element on both sides of the equation must be equal.

• For example,
  Hydrogen + Chlorine → Hydrogen chloride
  Unbalanced: H₂ + Cl₂ → HCl
  Balanced: H₂ + Cl₂ → 2HCl

Law of Conservation of Mass

• “Matter can neither be created nor destroyed; it can only be transformed from one form to another.”
• During a chemical reaction, the total mass of the reactants equals the total mass of the products.

Important Tips for Balancing Equations

• Always balance one element at a time.
• Begin with the compound that has the greatest number of atoms of any element.
• Never alter the subscripts within chemical formulas.
• Only adjust coefficients (numbers before symbols or formulas).
• Double-check that the number of atoms of each element is the same on both sides.

Trick for balance chemical equation (M-N-O-H)

• First balance metal.
• Then balance non-metal.
• Balance oxygen
• Balance hydrogen

Balance the following chemical equation :

1. H₂ + O₂ → H₂O
2. Na + H₂O → NaOH + H₂
3. Mg + O₂ → MgO
4. H₂ + N₂ → NH₃
5. Zn + HCl → ZnCl₂ + H₂
6. CH₄ + O₂ → CO₂ + H₂O
7. Fe + HCl → FeCl₂ + H₂
8. NaCl + AgNO₃ → AgCl + NaNO₃
9. Na₂O + H₂O → NaOH
10. BaCl₂ + H₂SO₄ → BaSO₄ + HCl
11. Mg(OH)₂ + HCl → MgCl₂ + H₂O
12. NaOH + H₂SO₄ → Na₂SO₄ + H₂O
13. H₂O₂ → H₂O + O₂
14. NaOH + HCl → NaCl + H₂O
15. H₂S + Cl₂ → HCl +
16. SCa(OH)₂ + CO₂ → CaCO₃ + H₂O
17. ZnCO₃    ZnO + CO₂
18. Zn + H₂SO₄ → ZnSO₄ + H₂
19. Fe + CuSO₄ → ZnSO₄ + Cu
20. CuSO₄ + H₂S → CuS + H₂SO₄
21. Na₂CO₃ + HCl → NaCl + H₂O + CO₂
22. CuSO₄ + NaOH → Cu(OH)₂ + Na₂SO₄
23. BaCl₂ + Al₂(SO₄)₃ → BaSO₄ + AlCl₃
24. HNO₃ + Ca(OH)₂ → Ca(NO₃)₂ + H₂O
25. Al(OH)₃ → Al₂O₃ + H₂O
26. Zn + NaOH  \(\xrightarrow{Heat}\)  Na₂ZnO₂ + H₂
27. Ca + HNO₃ → Ca(NO₃)₂ + H₂
28. Na + O₂ → Na₂O
29. Na₂SO₃ + HCl → NaCl + H₂O + SO₂
30. BaCl₂ + H₂SO₄ → BaSO₄ + HCl
31. Fe + H₂O → Fe₃O₄ + H₂
32. Fe + O₂ → Fe₂O₃
33. S + H₂SO₄ → SO₂ + H₂O
34. NH₃ + CuO → Cu + N₂ + H₂O
35. Pb(NO₃)₂ → PbO + NO₂ + O₂
36. Al₂(SO₄)₃ + NaOH → Al(OH)₃ + Na₂SO₄
37. Pb₃O₄ + HCl → PbCl₂ + H₂O + Cl₂
38. Zn + HNO₃ → Zn(NO₃)₂ + H₂O + N₂O
39. HNO₃ + H₂S → NO₂ + H₂O + S
40. CO₂ + H₂O  (\xrightarrow[{Chlorophyll}]{Sunlight}\)  C₆H₁₂O₆ + O₂
41. FeSO₄ → Fe₂O₃ + SO₂ + SO₃
42. Al + H₂SO₄ → Al₂(SO₄)₃ + H₂
43. Pb(NO₃)₂ + KI → PbI₂ + KNO₃

Write the balanced equation for the following chemical reactions:

1. Carbon + Oxygen ⟶ Carbon dioxide
2. Nitrogen + Oxygen ⟶ Nitrogen monoxide
3. Calcium + Nitrogen ⟶ Calcium nitride
4. Calcium oxide + Carbon dioxide ⟶ Calcium carbonate
5. Calcium oxide + Water ⟶ Calcium hydroxide
6. Sodium + Chlorine ⟶ Sodium chloride
7. Magnesium burns in oxygen to form magnesium oxide.
8. Hydrogen + Chlorine → Hydrogen chloride
9. Magnesium + Sulphuric acid ⟶ Magnesium sulphate + Hydrogen
10. Sodium + Water → Sodium hydroxide + Hydrogen
11. Zinc + Silver nitrate → Zinc nitrate + Silver
12. Aluminium + Copper chloride → Aluminium chloride + Copper
13. Iron + Sulphuric acid ⟶ Ferrous sulphate + Hydrogen
14. Sodium hydroxide + Sulphuric acid ⟶ Sodium sulphate + Water
15. Potassium bicarbonate + Sulphuric acid ⟶ Potassium sulphate + Carbon dioxide + Water
16. Magnesium(s) + Hydrochloric acid(aq) → Magnesium chloride(aq) + Hydrogen(g)
17. Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride
18. Barium chloride + Potassium sulphate → Barium sulphate + Potassium chloride
19. Copper sulphate + Sodium hydroxide → Copper hydroxide + Sodium sulphate
20. Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
21. Potassium bromide(aq) + Barium iodide(aq) → Potassium iodide(aq) + Barium bromide(s)
22. Zinc carbonate(s) → Zinc oxide(s) + Carbon dioxide(g)
23. Sodium metal reacts with water to give sodium hydroxide and hydrogen.
24. Hydrogen gas combines with nitrogen to form ammonia.
25. Solutions of Barium chloride and Sodium sulphate in water react to give insoluble Barium sulphate and the solution of Sodium chloride.
26. Iron (III) oxide reacts with Aluminium and gives molten iron and aluminium oxide.
27. Chlorine + Sulphur dioxide + Water ⟶ Sulphuric acid + Hydrogen chloride

Limitations of a Chemical Equation

A balanced equation gives limited information. It does not show:

1. The physical states of reactants and products.
2. The time taken for the reaction.
3. The rate of the reaction.
4. The heat changes involved (absorption or evolution).
5. The conditions like temperature, pressure, or catalysts.
6. The nature of the reaction (reversible or irreversible).
7. The concentration of reactants and products.

Making a Chemical Equation More Informative

A chemical equation can be made more descriptive by:

1. Indicating the physical states:

• (s) for solid
• (l) for liquid
• (g) for gas
• (aq) for aqueous solution

Example: CaCO₃(s) → CaO(s) + CO₂(g)

2. Indicating heat change:

• + heat on the product side → Heat is released (exothermic reaction)

• – heat or “heat absorbed” → Heat is absorbed (endothermic reaction)

3. The conditions under which a reaction takes place (such as temperature, pressure, catalyst, or light) are written above or below the arrow (→) in the equation.

4. Use dil. for dilute and conc. for concentrated solutions.

5. Indicating reversible or irreversible nature using arrows:

• (→) for irreversible
• (⇌) for reversible

Example:
Formation of Ammonia (Haber’s Process):

• Reaction is reversible and exothermic.

6. Important Symbols in Equations

• ↑ → Gas evolved
• ↓ → Precipitate formed
• Δ → Heat applied
• (aq) → Aqueous solution
• + heat → Exothermic reaction
• – heat → Endothermic reaction

Answer Key

Balance the following chemical equation:

1. 2H₂ + O₂ → 2H₂O
2. 2Na + 2H₂O → 2NaOH + H₂
3. 2Mg + O₂ → 2MgO
4. 3H₂ + N₂ → 2NH₃
5. Zn + 2HCl → ZnCl₂ + H₂
6. CH₄ + 2O₂ → CO₂ + 2H₂O
7. Fe + 2HCl → FeCl₂ + H₂
8. NaCl + AgNO₃ → AgCl + NaNO₃
9. Na₂O + H₂O → NaOH
10. BaCl₂ + H₂SO₄ → BaSO₄ + 2HCl
11. Mg(OH)₂ + 2HCl → MgCl₂ + 2H₂O
12. 2NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O
13. 2H₂O₂ → 2H₂O + O₂
14. NaOH + HCl → NaCl + H₂O
15. H₂S + Cl₂ → 2HCl + S
16. Ca(OH)₂ + CO₂ → CaCO₃ + H₂O
17. ZnCO₃     ZnO + CO₂
18. Zn + H₂SO₄ → ZnSO₄ + H₂
19. Fe + CuSO₄ → ZnSO₄ + Cu
20. CuSO₄ + H₂S → CuS + H₂SO₄
21. Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂
22. CuSO₄ + 2NaOH → Cu(OH)₂ + Na₂SO₄
23. 3BaCl₂ + Al₂(SO₄)₃ → 3BaSO₄ + 2AlCl₃
24. 2HNO₃ + Ca(OH)₂ → Ca(NO₃)₂ + 2H₂O
25. 2Al(OH)₃ → Al₂O₃ + 3H₂O
26. Zn + 2NaOH \(\xrightarrow{Heat}\) Na₂ZnO₂ + H₂
27. Ca + 2HNO₃ → Ca(NO₃)₂ + H₂
28. 4Na + O₂ → 2Na₂O
29. Na₂SO₃ + 2HCl → 2NaCl + H₂O + SO₂
30. BaCl₂ + H₂SO₄ → BaSO₄ + 2HCl
31. 3Fe + 4H₂O → Fe₃O₄ + 4H₂
32. 4Fe + 3O₂ → 2Fe₂O₃
33. S + 2H₂SO₄ → 3SO₂ + 2H₂O
34. 2NH₃ + 3CuO → 3Cu + N₂ + 3H₂O
35. 2Pb(NO₃)₂ → 2PbO + 4NO₂ + O₂
36. Al₂(SO₄)₃ + 6NaOH → 2Al(OH)₃ + 3Na₂SO₄
37. Pb₃O₄ + 8HCl → 3PbCl₂ + 4H₂O + Cl₂
38. 4Zn + 10HNO₃ → 4Zn(NO₃)₂ + 5H₂O + N₂O₂
39. HNO₃ + H₂S → 2NO₂ + 2H₂O + S
40. 6CO₂ + 6H₂O \(\xrightarrow[{Chlorophyll}]{Sunlight}\)   C₆H₁₂O₆ + 6O₂
41. 2FeSO₄ → Fe₂O₃ + SO₂ + SO₃
42. 2Al + 3H₂SO₄ → Al₂(SO₄)₃ + 3H₂
43. Pb(NO₃)₂ + 2KI → PbI₂ + 2KNO₃

Write the balanced equation for the following chemical reactions:

1. C + O₂ ⟶ CO₂
2. N₂ + O₂ ⟶ 2NO
3. 3Ca + N₂ ⟶ Ca₃N₂
4. CaO + CO₂ ⟶ CaCO₃
5. CaO + H₂O ⟶ Ca(OH)₂
6. 2Na + Cl₂ ⟶ 2NaCl
7. 2Mg + O₂ ⟶ 2MgO
8. H₂ + Cl₂ ⟶ 2HCl
9. Mg + H₂SO₄ ⟶ MgSO₄ + H₂
10. 2Na + 2H₂O ⟶ 2NaOH + H₂
11. Zn + 2AgNO₃ ⟶ Zn(NO₃)₂ + 2Ag
12. 2Al + 3CuCl₂ ⟶ 2AlCl₃ + 3Cu
13. Fe + H₂SO₄ ⟶ FeSO₄ + H₂
14. 2NaOH + H₂SO₄ ⟶ Na₂SO₄ + 2H₂O
15. 2KHCO₃ + H₂SO₄ ⟶ K₂SO₄ + 2CO₂ + 2H₂O
16. Mg + 2HCl ⟶ MgCl₂ + H₂
17. 3BaCl₂ + Al₂(SO₄)₃ ⟶ 3BaSO₄ + 2AlCl₃
18. BaCl₂ + K₂SO₄ ⟶ BaSO₄ + 2KCl
19. CuSO₄ + 2NaOH ⟶ Cu(OH)₂ + Na₂SO₄
20. Ca(OH)₂ + CO₂ ⟶ CaCO₃ + H₂O
21. 2KBr + BaI₂ ⟶ 2KI + BaBr₂
22. ZnCO₃ ⟶ ZnO + CO₂
23. 2Na + 2H₂O ⟶ 2NaOH + H₂
24. N₂ + 3H₂ ⟶ 2NH₃
25. BaCl₂ + Na₂SO₄ ⟶ BaSO₄ + 2NaCl
26. Fe₂O₃ + 2Al ⟶ Al₂O₃ + 2Fe
27. Cl₂ + SO₂ + 2H₂O ⟶ H₂SO₄ + 2HCl

Students looking for ICSE Class 8 Language of Chemistry Notes PDF Download can use these notes for quick revision and concept clarity. These notes cover atom structure, subatomic particles, electronic configuration, atomic number, mass number, and valency in an easy format.

Conclusion

ICSE Class 8 Chemistry Language of Chemistry Notes are essential for building a strong foundation in chemistry. By learning symbols, valency, radicals, and formulas, students can understand chemical reactions more effectively and score better in examinations.

ICSE Class 8 Chemistry Notes

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