Atoms and Molecules – Long Answer Questions
Medium Level (Application & Explanation)
Q1. Explain how the number of protons decides the identity of an element. Use suitable examples.
Answer:
- The identity of an element is set by its atomic number.
- The atomic number is the count of protons in the nucleus.
- Hydrogen has 1 proton, while Oxygen has 8 protons, so they are different.
- Carbon has 6 protons, but Nitrogen has 7 protons, so they are different.
- If you change the number of protons, you change the element.
- Atoms of the same element always have the same number of protons.
- This rule helps us clearly tell one element from another.
Q2. Describe the structure of an atom with focus on the location and charges of sub-atomic particles.
Answer:
- An atom has a small nucleus at the center.
- The nucleus contains protons and neutrons.
- Protons carry a +1 charge.
- Neutrons have no charge.
- Electrons move around the nucleus and carry a -1 charge.
- In a neutral atom, the number of electrons equals the number of protons.
- This balance keeps the atom uncharged overall.
Q3. What are isotopes? Explain how atoms of the same element can still differ.
Answer:
- Atoms of the same element have the same number of protons.
- But they can have different numbers of neutrons.
- Such atoms are called isotopes.
- Their chemical identity stays the same because protons are the same.
- Their mass changes because neutrons change.
- For example, two carbon atoms can have different neutrons but both have 6 protons.
- So, they are the same element but different isotopes.
Q4. Compare Sulfur and Phosphorus in terms of atomic structure and charge neutrality.
Answer:
- Sulfur has 16 protons, and Phosphorus has 15 protons.
- In a neutral atom, electrons equal protons.
- So, neutral Sulfur has 16 electrons, and neutral Phosphorus has 15 electrons.
- Both have neutrons in the nucleus along with protons.
- Their atomic numbers (16 and 15) make them different elements.
- Each can be neutral if positive and negative charges balance.
- So, both can be neutral but are still different due to proton count.
Q5. Explain the contributions of J.J. Thomson and Ernest Rutherford to our understanding of the atom.
Answer:
- J.J. Thomson discovered the electron.
- Electrons are negatively charged particles.
- Ernest Rutherford identified the proton.
- Protons are positively charged and heavier than electrons.
- These discoveries showed atoms have sub-atomic particles.
- They proved atoms are not indivisible.
- They supported the idea of a nucleus with protons and electrons around it.
High Complexity (Analysis & Scenario-Based)
Q6. An oxygen atom gains two electrons. Explain the new charge and whether it remains the same element.
Answer:
- Oxygen has 8 protons in its nucleus.
- A neutral oxygen atom also has 8 electrons.
- Gaining 2 electrons makes the electron count 10.
- Negative charge now exceeds positive charge by 2.
- So, it becomes negatively charged with a net charge of -2.
- The element is still oxygen because the number of protons did not change.
- Electrons changed, but identity depends on protons.
Q7. A nitrogen nucleus loses one proton in a process. What happens to the identity of the atom? Explain.
Answer:
- Nitrogen has 7 protons.
- Losing one proton reduces the count to 6.
- An atom with 6 protons is carbon.
- So, the atom’s identity changes to carbon.
- Identity depends only on the number of protons.
- Electrons may adjust later, but that does not fix the identity.
- Neutrons do not decide which element it is.
Q8. Two atoms each have 6 protons. One has 6 neutrons, the other has 7. Compare their identity, mass, and charge.
Answer:
- Both have 6 protons, so both are carbon.
- They differ in neutron count: 6 vs 7.
- They are isotopes of carbon.
- Their mass is different because neutrons add mass.
- Both can be neutral if electrons equal protons.
- Their chemical identity is the same due to equal protons.
- They are not different elements, only different isotopes.
Q9. A helium atom loses both its electrons. Describe what remains, the charge on it, and whether it is still helium.
Answer:
- Helium has 2 protons in its nucleus.
- A neutral helium atom also has 2 electrons.
- Losing both electrons leaves 0 electrons.
- Positive charge from protons is now unbalanced.
- The particle becomes +2 charged overall.
- Neutrons (if any) remain in the nucleus with protons.
- It is still helium, because identity depends on protons.
Q10. Two samples are given: X has 8 protons and 7 electrons. Y has 8 protons and 8 electrons. Analyze their charges and identities.
Answer:
- Both have 8 protons, so both are oxygen by identity.
- Sample X has fewer electrons than protons.
- So, X is positively charged with a net charge of +1.
- Sample Y has equal protons and electrons.
- So, Y is neutral with no net charge.
- Changing electrons changes the charge, not the element.
- Identity stays the same because protons are the same.