Chapter 3 Atoms and Molecules

 Chapter 3   Atoms and Molecules                                                                                                                               

**History of the Atom**

*   **Q: Which ancient Indian philosopher named the smallest indivisible particles of matter "Parmanu"?** 

    **A:** Maharishi Kanad.

*   **Q: Which ancient Greek philosophers suggested the name "atoms" (meaning indivisible) for the smallest particles of matter?** 

    **A:** Democritus and Leucippus.

**Laws of Chemical Combination**

*   **Q: Who laid the foundation of chemical sciences by establishing two important laws of chemical combination?** 

    **A:** Antoine L. Lavoisier.

*   **Q: What does the law of conservation of mass state?** 

    **A:** It states that mass can neither be created nor destroyed in a chemical reaction.

*   **Q: What is the constant ratio by mass of hydrogen to oxygen in a water molecule?** 

    **A:** The ratio is always 1:8, regardless of the source of the water.

*   **Q: Which British chemist provided the atomic theory that explained the laws of chemical combination?** 

    **A:** John Dalton.

**Atoms and Symbols**

*   **Q: What unit is used to measure the atomic radius of an atom?** 

    **A:** Nanometres (nm).

*   **Q: Which scientific organization is responsible for approving the names, symbols, and units of elements?** 

    **A:** IUPAC (International Union of Pure and Applied Chemistry).

*   **Q: From what Latin names are the symbols for iron (Fe), sodium (Na), and potassium (K) derived?** 

    **A:** Ferrum (Iron), Natrium (Sodium), and Kalium (Potassium).

**Atomic Mass**

*   **Q: What isotope was universally chosen in 1961 as the standard reference for measuring atomic masses?** 

    **A:** The carbon-12 isotope.

*   **Q: How is one atomic mass unit (u) formally defined?** 

    **A:** It is a mass unit equal to exactly one-twelfth (1/12th) the mass of one atom of carbon-12.

**Molecules and Ions**

*   **Q: What is the term for the number of atoms that constitute a single molecule?** 

    **A:** Atomicity.

*   **Q: What is an ion?** 

    **A:** A charged species that consists of a single charged atom or a group of atoms with a net charge.

*   **Q: What are negatively and positively charged ions called?** 

    **A:** A negatively charged ion is called an anion, and a positively charged ion is called a cation.

*   **Q: What do we call a group of atoms carrying a charge?** 

    **A:** A polyatomic ion.

*   **Q: What term describes the combining power or capacity of an element?** 

    **A:** Valency.

**Molecular Mass**

*   **Q: How do you calculate the molecular mass of a substance?** 

    **A:** By finding the sum of the atomic masses of all the atoms present in a molecule of that substance.

*   **Q: For which types of substances do we use the term "formula unit mass" instead of molecular mass?** 

    **A:** For substances whose constituent particles are ions (like sodium chloride).