Question 1

Which experiment led to the discovery of the electron, and what was the main observation that supported this discovery?

Accepted Answer

J.J. Thomson's cathode ray experiment; observation of rays deflected by electric and magnetic fields

Question 2

According to Dalton's atomic theory, which statement is INCORRECT?

Accepted Answer

Atoms can be created or destroyed in chemical reactions.

Question 3

In Rutherford’s alpha particle scattering experiment, most alpha particles passed straight through the gold foil. What does this observation imply about the structure of the atom?

Accepted Answer

Atoms are mostly empty space with a small, dense nucleus.

Question 4

Which of the following best describes the arrangement of electrons in Bohr’s atomic model?

Accepted Answer

Electrons revolve in fixed, permitted circular orbits around the nucleus.

Question 5

A neutral atom of sodium has an atomic number of 11 and a mass number of 23. How many neutrons does it contain?

Accepted Answer

$$23 - 11 = 12$$

Question 6

Which property of cathode rays was demonstrated by their deflection in both electric and magnetic fields?

Accepted Answer

They are negatively charged particles.

Question 7

Which statement about isotopes is correct?

Accepted Answer

Isotopes have the same atomic number but different mass numbers.

Question 8

What is the electronic configuration of an atom with atomic number 14?

Accepted Answer

$$1s^2$$ $$2s^2$$ $$2p^6$$ $$3s^2$$ $$3p^2$$

Question 9

Which of the following is a drawback of Rutherford’s atomic model?

Accepted Answer

It could not explain the stability of the atom due to electron acceleration.

Question 10

If an atom has 8 protons, 8 neutrons, and 8 electrons, what is its atomic number and mass number?

Accepted Answer

Atomic number = $$8$$, Mass number = $$16$$

Question 11

Which experiment provided evidence for the existence of protons?

Accepted Answer

Goldstein’s canal ray experiment

Question 12

What is the maximum number of electrons that can be accommodated in the M shell (third shell) of an atom?

Accepted Answer

$$2n^2$$ where $$n=3$$, so $$2 	imes 3^2$ = 18$$

Question 13

Which statement about Bohr’s atomic model is correct?

Accepted Answer

Electrons revolve in certain permitted orbits without emitting energy.

Question 14

Which of the following particles has no charge and a mass nearly equal to that of a proton?

Accepted Answer

Neutron

Question 15

If the atomic number of an element is $$Z$$ and its mass number is $$A$$, what is the number of neutrons in the atom?

Accepted Answer

$$A - Z$$

Question 16

Which of the following best explains why cathode rays are deflected by electric and magnetic fields?

Accepted Answer

Cathode rays are composed of negatively charged particles.

Question 17

Which of the following is NOT a postulate of Dalton’s atomic theory?

Accepted Answer

Atoms can be divided into protons, neutrons, and electrons.

Question 18

What is the electronic configuration of an atom with atomic number 20?

Accepted Answer

$$1s^2$$ $$2s^2$$ $$2p^6$$ $$3s^2$$ $$3p^6$$ $$4s^2$$

Question 19

Which of the following statements about the nucleus of an atom is correct according to Rutherford’s model?

Accepted Answer

The nucleus is a small, dense region containing protons and neutrons.

Atomic Structure: Foundations of the Atom

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