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Pg:- 69,70,71,72,73,74,75

Ch:- 4

Chemical names and formulae are essential in chemistry to represent substances. The chemical name identifies the substance, and the formula represents the elements and their quantities in the compound.

1. Elements

• Name: Each element has a unique name, like Oxygen or Hydrogen.

• Symbol: Elements are denoted by one or two letters, e.g., O for Oxygen, H for Hydrogen.

• Formula: The formula for an element is its symbol, e.g., O for oxygen or H for hydrogen.

2. Compounds

Compounds are made from two or more elements chemically bonded together. Their formulae indicate the proportion of elements in the compound.

Ionic Compounds

These are formed from ions, which are charged atoms or groups of atoms.

• Naming: The metal (or positive ion) is named first, followed by the non-metal (or negative ion). The non-metal's name often ends in "-ide."

  • Example: Sodium Chloride (NaCl).

• Formula: The ionic formula is written by balancing the charges of the ions.

  • Example: Na⁺ (Sodium) and Cl⁻ (Chloride) combine to form NaCl.

Covalent Compounds

These are formed when atoms share electrons.

• Naming: Prefixes are used to indicate the number of atoms (mono-, di-, tri-, etc.). The second element’s name ends in "-ide."

  • Example: Carbon Dioxide (CO₂).

• Formula: The formula is written based on the number of atoms of each element.

  • Example: CO₂ means 1 carbon atom and 2 oxygen atoms.

Acids

Acids often contain hydrogen and one or more non-metals.

• Naming: Binary acids (hydrogen + non-metal) are named with the prefix "hydro-" and the suffix "-ic" added to the root of the non-metal name, followed by "acid."

  • Example: Hydrochloric Acid (HCl).

• Formula: The chemical formula shows the hydrogen ion and the anion it bonds with.

  • Example: HCl for hydrochloric acid.

Bases

These are compounds that produce hydroxide ions (OH⁻) in solution.

• Naming: Bases are named by stating the cation first, followed by "hydroxide."

  • Example: Sodium Hydroxide (NaOH).

• Formula: The formula reflects the cation and hydroxide group.

  • Example: NaOH.

3. Molecular Compounds

• Naming: Prefixes are used to indicate the number of each element present, but "mono-" is usually omitted for the first element.

  • Example: Sulfur Hexafluoride (SF₆).

• Formula: The formula corresponds to the number of each atom present in the compound.

  • Example: SF₆ for sulfur hexafluoride.

4. Organic Compounds

These are primarily made of carbon and hydrogen, sometimes with oxygen, nitrogen, or other elements.

• Naming: Organic compounds are named based on the number of carbon atoms and the types of bonds (single, double, triple). Functional groups also influence the name.

  • Example: Methane (CH₄) is the simplest alkane with one carbon atom.

• Formula: Organic compounds have various structures, but the molecular formula indicates the number of each type of atom.

  • Example: Ethanol (C₂H₆O).

Common Prefixes Used in Naming Compounds:

1. Mono- (1)

2. Di- (2)

3. Tri- (3)

4. Tetra- (4)

5. Penta- (5)

6. Hexa- (6)

7. Hepta- (7)

8. Octa- (8)

9. Nona- (9)

10. Deca- (10)

5. Hydrates

Some compounds incorporate water molecules into their structure, known as hydrates.

• Naming: The name of the compound is followed by a prefix indicating the number of water molecules and the word "hydrate."

  • Example: Copper(II) sulfate pentahydrate (CuSO₄·5H₂O).

• Formula: The chemical formula includes the number of water molecules.

  • Example: CuSO₄·5H₂O.

Examples of Common Chemical Formulae:

1. Water – H₂O

2. Carbon Dioxide – CO₂

3. Methane – CH₄

4. Ammonia – NH₃

5. Sulfuric Acid – H₂SO₄

6. Sodium Bicarbonate – NaHCO₃

7. Calcium Carbonate – CaCO₃

8. Glucose – C₆H₁₂O₆