Subatomic Particles Electron Proton Neutron - UNSOLVED PRACTICE SET

Q7. Name the three fundamental subatomic particles and state their charges and relative masses. 

Q8. Who discovered the neutron? How was it different from the discovery of the proton and electron? 

Q9. What are cathode rays? How did their study lead to the discovery of the electron? 

Q10. Why is the mass of an electron considered negligible when calculating the mass of an atom? 

Q11. Your physics teacher demonstrates a discharge tube experiment in the darkened lab. You see a greenish glow at the end of the tube where the cathode rays strike. She explains that these rays are actually streams of electrons. If electrons are negatively charged, why do they travel from the cathode (negative) towards the anode (positive)?

Q12. An ion has 17 protons, 18 neutrons, and 18 electrons. What is its charge? Identify the element and write its symbol.

Q13. Describe the properties of electrons, protons, and neutrons in detail. Compare them on the basis of:

(a) Charge

(b) Mass

(c) Location in the atom

(d) Discovery and experimental evidence

How do these three particles together determine the identity and properties of an atom?

Q14. Explain how J.J. Thomson discovered the electron through his cathode ray tube experiments. What properties of cathode rays did he observe? How did he determine the charge-to-mass ratio (e/m) of the electron? Why was this discovery revolutionary for atomic theory?

Q15. During a class discussion, your teacher asks you to imagine being a scientist in 1932, just after James Chadwick discovered the neutron.

(a) How would you explain the existence of isotopes using the concept of neutrons?

(b) Why did the discovery of the neutron solve the problem of atomic mass not being a whole number multiple of the proton mass?

(c) If oxygen-16 has 8 protons and 8 neutrons, but oxygen-17 has 8 protons and 9 neutrons, what does this tell you about the relationship between an element's identity and its subatomic particles?

(d) A student argues: "Since neutrons have no charge, they don't matter in chemistry." How would you counter this argument?

Q16. The charge on an electron is −1.6 × 10⁻¹⁹ C and its mass is 9.1 × 10⁻³¹ kg.

(a) Calculate the charge-to-mass ratio (e/m) of the electron in C/kg.

(b) If a beam of electrons carries a total charge of 3.2 × 10⁻¹⁸ C, how many electrons are present in the beam?

(c) Calculate the total mass of these electrons.

Q17. An atom of element X has 35 protons, 45 neutrons, and 35 electrons. Another atom of element Y has 35 protons, 47 neutrons, and 36 electrons.

(a) Identify elements X and Y. Are they isotopes? Explain.

(b) Calculate the mass number of both atoms.

(c) What is the charge on atom Y? What do we call such a species?

(d) If element X forms a negative ion by gaining 1 electron, how many electrons will it have? What will be its charge?

Q18. In Millikan's oil drop experiment, an oil droplet of mass 1.6 × 10⁻¹⁴ kg is suspended between two charged plates. The electric field required to balance the droplet is 2.0 × 10⁵ N/C upward.

(a) Calculate the charge on the oil droplet. (Take g = 9.8 m/s²)

(b) How many excess electrons does this droplet carry?

(c) Why did Millikan use oil droplets instead of water droplets for this experiment?

(Charge on electron = 1.6 × 10⁻¹⁹ C)