Atoms and Molecules Notes Important Question Answer

Atoms and Molecules Notes Important Question Answer

Atoms and Molecules Notes Important Question Answer

1. Atoms-The smallest particle that reveals all the properties of an element is called an atom which cannot exist in an independent state.

2. Molecule-The smallest particle made of atoms and can exist independently is called a molecule which reveals all the characteristics of a substance.

3. Atomic Mass-The weight of an atom of an element which is 1/12th of the weight of an atom of carbon is called the atomic mass of that element, whereas the weight of a carbon atom is taken as 12.

4. Isotopes-Isotopes are different atoms of an element which have the same atomic number but different atomic weights.

5. Molecular Mass-The sum of the total mass of all the atoms present in the molecule of a substance is called molecular mass. 6. Atomic Mass Unit-1/12 of the mass of a particular isotope of an atom of carbon (C-12) is called atomic mass unit (u).

7. Mole-Mole is the mass of a substance which contains particles similar to 12g of carbon C2 atom. Those particles can be in the form of atoms, molecules or ions. 6.023 x 10-23 of a substance is called one mole.

8. Empirical Formula-The formula which shows the ratio in the number of atoms of different elements present in the molecules is called empirical formula.

9. Molecular Formula-Molecular formula shows the actual number of atoms of different elements in the molecule of the compound.

10. Law of Conservation of Mass- In a chemical reaction, the total mass of the substance reacting remains equal to the mass of the substance formed after the reaction.

In chemical reactions, substances are never destroyed, only their form changes.

11. Avogadro’s Number- All gases have the same number of molecular masses per gram. This number is called Avogadro’s Number. It is represented by N and its value is 6.023 x 10-23.

12. Law of Constant Proportions- The law of constant proportions states that a chemical compound is always made up of the same elements and the proportion of those elements always remains the same in terms of weight and quantity.

13. Ions- The charged particles from which the compounds of metals and non-metals are made are called ions. 14. Anion- Negatively charged particles are called anions.

15. Cation- Positively charged particles are called cations.

Atoms and Molecules Notes Important Question Answer

Q1. When did Indian philosophers first consider the divisibility of matter?
A. Around 500 BCE.
Q2. What did Maharishi Kanada propose?
A. The smallest particle of matter is indivisible.
Q3. What name did Maharishi Kanada give to the indivisible smallest particle?
A. Parmanu (atom).
Q4. What did the Indian philosopher Pakava Katyayana say about particles?
A. Particles are generally found in a combined state, which gives substances their different forms.
Q5. Which two Greek philosophers considered the particle indivisible?
A. Democritus and Leucippus.
Q6. Until which century was no experimental work done on particles?
A. Until the 18th century.
Q7. Who established the important laws of chemical combination?
A. Antoine L. Lavoisier.
Q8. What is the law of conservation of mass?
A. When a chemical change occurs, mass is neither created nor destroyed.
Q9. What is the law of definite proportions?
A. In a compound made from two or more elements, the ratio of the elements is fixed, regardless of where the compound is obtained or who made it.
Q10. What is the mass ratio of hydrogen to oxygen in water?
A. 1:8.
Q11. What is the mass ratio of nitrogen to hydrogen in ammonia (NH₃)?
A. 14:3.
Q12. What did Proust say under the law of definite proportions?
A. In any compound, the elements are always present in a definite proportion.
Q13. When did John Dalton present the atomic theory?
A. In 1808.
Q14. Who presented the fundamental theory about the nature of substances?
A. John Dalton.
Q15. What was Dalton’s theory based on?
A. The laws of chemical combination.
Q16. According to Dalton’s theory, what are all substances made of?
A. Tiny particles.
Q17. What is an atom?
A. The smallest unit of matter.
Q18. How large are atoms?
A. Atoms are very small. Stacking millions of atoms on top of each other would be about the thickness of a sheet of paper.
Q19. In what units is atomic radius measured?
A. Nanometers (nm).
Q20. How much is one nanometer?
A. 1 nm = 10⁻⁹ meters.
Q21. What are the radii (in meters) of hydrogen atoms, water molecules, hemoglobin molecules, sand particles, ants, and watermelons?
A. Hydrogen atom = 10⁻¹⁰, water molecule = 10⁻⁹, hemoglobin molecule = 10⁻⁸, sand particle = 10⁻⁴, ant = 10⁻², watermelon = 10⁻¹.
Q22. What is the entire universe made of?
A. Atoms.
Q23. Who first used symbols for elements?
A. Dalton.
Q24. What was special about Berzelius’ symbols?
A. They were represented by one or two letters of the element’s name.
Q25. From where is the name of Copper (Cu) derived?
A. From Cyprus.
Q26. From where is the name of Gold (Au) derived?
A. From the English word meaning yellow.
Q27. What is the full form of IUPAC?
A. International Union of Pure and Applied Chemistry.
Q28. How are most symbols made?
A. From one or two letters of the English names of the elements.
Q29. On which languages are the symbols based?
A. English, Latin, German, and Greek.
Q30. On which language’s word is the symbol for iron based?
A. On the Latin word ‘ferrum’.
Q31. From where are the symbols for sodium and potassium derived?
A. From ‘natrium’ and ‘kalium’.
Q32. What was the most distinctive concept of Dalton’s atomic theory?
A. The concept of atomic mass.
Q33. How were atomic masses determined?
A. Using the laws of chemical combination and the resulting compounds.
Q34. How were atomic masses previously abbreviated?
A. With ‘amu’ (atomic mass unit).
Q35. How are atomic masses now represented with IUPAC approval?
A. With ‘u’ (unified mass).
Q36. On what basis were the units of various atomic masses taken earlier?
A. On the basis of 1/16 of the mass of an oxygen atom.
Q37. Since when has the carbon-12 isotope been universally accepted as the unit of mass?
A. Since 1961.
Q38. How is atomic mass taken now?
A. As 1/12 of the mass of a C-12 atom.
Q39. What do atoms form?
A. Atoms form molecules and ions.
Q40. What forms matter?
A. Molecules or ions in large numbers form matter.
Q41. What is a molecule?
A. Generally, a molecule is a group of two or more atoms bonded together by chemical bonds or held together by mutual attraction.
Q42. What is the smallest particle of an element or compound that can exist independently?
A. A molecule.
Q43. What is made up of only one type of atom in an element?
A. A molecule.
Q44. How many oxygen atoms make up oxygen?
A. Two atoms, hence it is called a diatomic molecule.
Q45. Give four examples of diatomic molecules.
A. Hydrogen, oxygen, nitrogen, chlorine.
Q46. Give an example of a tetratomic molecule.
A. Phosphorus.
Q47. Give an example of a polyatomic molecule.
A. Sulfur.
Q48. What is formed when three oxygen atoms combine?
A. Ozone (O₃).
Q49. Which element’s molecules do not have a simple structure?
A. Carbon.
Q50. What is the mass ratio of carbon to oxygen in carbon dioxide?
A. 3:8.


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