Chemistry Class 9th CBSE | Chapter - Structure of Atoms

Flashcards on the Discovery of Atomic Particles

• Flashcard 1: Who proposed that atoms are indivisible?

• Answer: Dalton [1, 2]

• Flashcard 2: In what year did Dalton propose his atomic theory?

• Answer: 1808 [2]

• Flashcard 3: What experiment did J.J. Thomson conduct?

• Answer: Cathode Ray Experiment [2]

• Flashcard 4: What did the cathode ray experiment prove?

• Answer: The existence of negatively charged particles (electrons) within the atom [3]

• Flashcard 5: What are the conditions required for the Cathode Ray Experiment?

• Answer: Low pressure and high voltage in a vacuum tube [3]

• Flashcard 6: What is the charge of an electron?

• Answer: -1.6 x 10^-19 Coulombs [4]

• Flashcard 7: What is the mass of an electron?

• Answer: Negligible [4]

• Flashcard 8: Who discovered the proton?

• Answer: E. Goldstein [4, 5]

• Flashcard 9: What experiment led to the discovery of the proton?

• Answer: Anode ray or canal ray experiment [5]

• Flashcard 10: What is the charge of a proton?

• Answer: +1.6 x 10^-19 Coulombs [5]

• Flashcard 11: How does the mass of a proton compare to the mass of an electron?

• Answer: The mass of a proton is about 2000 times greater than the mass of an electron [5]

• Flashcard 12: Who discovered the neutron?

• Answer: James Chadwick [6]

• Flashcard 13: In what year was the neutron discovered?

• Answer: 1932 [6]

• Flashcard 14: What is the charge of a neutron?

• Answer: Zero (neutral) [6]

• Flashcard 15: How does the mass of a neutron compare to the mass of a proton?

• Answer: They are almost equal [6]

Flashcards on Atomic Models

• Flashcard 16: What model did J.J. Thomson propose for the structure of the atom?

• Answer: The plum pudding or watermelon model [7]

• Flashcard 17: According to Thomson's model, how are positive and negative charges distributed in an atom?

• Answer: Positive charge is uniformly distributed, and negative charges (electrons) are embedded within it [7]

• Flashcard 18: What did Thomson's model state about the overall charge of an atom?

• Answer: The overall charge is neutral [7]

• Flashcard 19: What was the name of the experiment conducted by Rutherford?

• Answer: Gold Foil Experiment [8]

• Flashcard 20: What type of particles were used in Rutherford's experiment?

• Answer: Alpha particles [9]

• Flashcard 21: What is an alpha particle?

• Answer: A positively charged particle, which is a double charged helium ion [9]

• Flashcard 22: Why was gold foil used in Rutherford's experiment?

• Answer: Gold is highly malleable and can be made into very thin sheets [10]

• Flashcard 23: What were the key observations of Rutherford’s gold foil experiment?

• Answer:

• Most alpha particles passed straight through [11]

• Some alpha particles were deflected at an angle [11]

• A very small number of alpha particles were reflected back [11]

• Flashcard 24: What were the main conclusions drawn from the Rutherford experiment?

• Answer:

• Most of the space in an atom is empty [11]

• The atom has a dense, positively charged nucleus [12]

• The nucleus is very small compared to the atom [12]

• Most of the atom's mass is concentrated in the nucleus [12]

• Flashcard 25: According to Rutherford, how do electrons move in an atom?

• Answer: Electrons revolve around the nucleus in well-defined orbits [13]

• Flashcard 26: What was the major drawback of Rutherford’s model?

• Answer: It could not explain the stability of atoms [13]

• Flashcard 27: What did Bohr propose regarding electron orbits?

• Answer: Electrons revolve in discrete (special) orbits without radiating energy [14]

• Flashcard 28: What are the different names given to these discrete orbits by Bohr?

• Answer: Energy shells or energy levels [14, 15]

• Flashcard 29: What are the names of the energy levels/shells?

• Answer: K, L, M, N [15]

• Flashcard 30: What is the ground state of an electron?

• Answer: The lowest energy level which is the K shell [15]

• Flashcard 31: When do electrons emit or absorb energy according to Bohr's model?

• Answer: When they jump from one orbit to another [15]

• Flashcard 32: How is energy emitted or absorbed when electrons jump?

• Answer:

• Electrons emit energy when jumping from a higher energy level to lower energy level [16]

• Electrons absorb energy when jumping from a lower to higher energy level [16]

Flashcards on Atomic Number and Mass Number

• Flashcard 33: What is atomic number?

• Answer: The number of protons in an atom [16]

• Flashcard 34: How is atomic number represented?

• Answer: By the letter Z [17]

• Flashcard 35: In a neutral atom, how do the number of protons and electrons compare?

• Answer: They are equal [17]

• Flashcard 36: Why is the number of protons used to define atomic number rather than electrons or neutrons?

• Answer: Because the number of protons is constant for a given element, while electrons can be gained or lost, and the number of neutrons can vary [17]

• Flashcard 37: What is mass number?

• Answer: The sum of protons and neutrons in an atom's nucleus [18]

• Flashcard 38: How is mass number represented?

• Answer: By the letter A [18]

• Flashcard 39: What is another name for mass number?

• Answer: Nucleon number [19]

• Flashcard 40: How do you calculate the number of neutrons in an atom, given its mass number and atomic number?

• Answer: Mass number - Atomic number [19]

• Flashcard 41: If an atom has an atomic number of 10 and a mass number of 22 how many protons, neutrons and electrons does it have?

• Answer:

• Protons - 10

• Neutrons - 12

• Electrons - 10 (if neutral) [19]

Flashcards on Electron Distribution

• Flashcard 42: What formula determines the maximum number of electrons a shell can hold?

• Answer: 2n² where 'n' is the shell number [20]

• Flashcard 43: What is the maximum number of electrons the K shell can hold?

• Answer: 2 [20]

• Flashcard 44: What is the maximum number of electrons the L shell can hold?

• Answer: 8 [20]

• Flashcard 45: What is the maximum number of electrons the M shell can hold?

• Answer: 18 [20]

• Flashcard 46: What is the maximum number of electrons the N shell can hold?

• Answer: 32 [20]

• Flashcard 47: What is the maximum number of electrons in the outermost shell of an atom?

• Answer: 8 [21]

• Flashcard 48: Which shell must be filled first, according to the distribution rule?

• Answer: The smallest shell or the inner shell [21]

• Flashcard 49: What is electronic configuration?

• Answer: The distribution of electrons in different shells of an atom [22]

• Flashcard 50: What is the electronic configuration of aluminum?

• Answer: 2, 8, 3 [22]

• Flashcard 51: What is the electronic configuration of calcium?

• Answer: 2, 8, 8, 2 [22]

• Flashcard 52: What is the electronic configuration of chlorine?

• Answer: 2, 8, 7 [23]

• Flashcard 53: What is the electronic configuration of a sodium ion (Na+)?

• Answer: 2, 8 (it loses one electron) [24]

• Flashcard 54: What is the electronic configuration of calcium ion (Ca+2)?

• Answer: 2, 8, 8 (it loses two electrons) [18, 24]

Flashcards on Valency

• Flashcard 55: Why do atoms combine with each other?

• Answer: To achieve stability, by attaining a noble gas electronic configuration, with 8 electrons in their outermost shell (octet rule) or 2 in the case of the first shell (duplet) [25]

• Flashcard 56: What are valence electrons?

• Answer: The electrons present in the outermost shell of an atom [26]

• Flashcard 57: What is valency?

• Answer: The combining capacity of an atom, or the number of electrons an atom will lose, gain, or share to achieve stability [26, 27]

• Flashcard 58: What is the valency of chlorine?

• Answer: 1 (it needs to gain 1 electron) [27]

• Flashcard 59: What is the valency of oxygen?

• Answer: 2 (it needs to gain 2 electrons) [27]

• Flashcard 60: What is the valency of lithium?

• Answer: 1 (it loses 1 electron) [27]

• Flashcard 61: If an atom has 1, 2, 3, or 4 electrons in its outermost shell, what is its valency?

• Answer: The same as the number of valence electrons, respectively. (1, 2, 3 or 4 respectively) [28]

• Flashcard 62: If an atom has 5, 6, 7, or 8 electrons in its outermost shell, how do you determine its valency?

• Answer: Subtract the number of valence electrons from 8 [28]

• Flashcard 63: What is the exception to the rules for determining valency?

• Answer: Helium whose valency is zero even with two electrons in its outer shell [28]

• Flashcard 64: What is the valency of boron?

• Answer: 3 [24]

• Flashcard 65: What is the valency of carbon?

• Answer: 4 [24]

• Flashcard 66: What is the valency of nitrogen?

• Answer: 3 [24]

• Flashcard 67: What is the valency of oxygen?

• Answer: 2 [24]

• Flashcard 68: What is the valency of fluorine?

• Answer: 1 [24]

Flashcards on Isotopes

• Flashcard 69: What are isotopes?

• Answer: Atoms of the same element with the same atomic number but different mass numbers [29]

• Flashcard 70: What is the key difference between isotopes?

• Answer: They have a different number of neutrons [29]

• Flashcard 71: How many isotopes of hydrogen are there?

• Answer: Three [29, 30]

• Flashcard 72: What are the names of the isotopes of hydrogen?

• Answer: Protium, Deuterium, and Tritium [30]

• Flashcard 73: What is the atomic number and mass number of Protium?

• Answer: Atomic Number - 1, Mass number - 1 [30]

• Flashcard 74: What is the atomic number and mass number of Deuterium?

• Answer: Atomic Number - 1, Mass number - 2 [30]

• Flashcard 75: What is the atomic number and mass number of Tritium?

• Answer: Atomic Number - 1, Mass number - 3 [30]

• Flashcard 76: How do the chemical properties of isotopes compare?

• Answer: They have identical chemical properties [30, 31]

• Flashcard 77: Why do isotopes of an element have similar chemical properties?

• Answer: Because they have the same number of protons and electrons [30, 31]

• Flashcard 78: How do the physical properties of isotopes compare?

• Answer: They have different physical properties [31]

• Flashcard 79: What is a use of Uranium isotopes?

• Answer: As fuel in nuclear reactors [31]

• Flashcard 80: What is a use of Cobalt isotopes?

• Answer: In the treatment of cancer [31]

• Flashcard 81: What is a use of Iodine isotopes?

• Answer: In the treatment of goiter [31]

• Flashcard 82: Why do some elements have fractional atomic masses?

• Answer: Because they are a mixture of different isotopes, and the atomic mass is an average of these different isotopes [31, 32]

Flashcards on Isobars

• Flashcard 83: What are isobars?

• Answer: Atoms of different elements with the same mass number but different atomic numbers [32, 33]

• Flashcard 84: What is the key difference between isobars?

• Answer: They have a different number of protons and neutrons [33]

• Flashcard 85: Give an example of isobars.

• Answer: Argon, Potassium and Calcium [33]

• Flashcard 86: What is a common mass number of the isobars Argon, Potassium and Calcium?

• Answer: 40 [33]

• Flashcard 87: How do the chemical properties of isobars compare?

• Answer: They have different chemical properties [33]

• Flashcard 88: Why do isobars of an element have different chemical properties?

• Answer: Because they have a different number of protons and electrons [33]

• Flashcard 89: How do the physical properties of isobars compare?

• Answer: They have similar physical properties [33]

Flashcards on Key Differences

• Flashcard 90: What is the key difference between isotopes and isobars with respect to atomic and mass numbers?

• Answer: Isotopes have same atomic numbers and different mass numbers. Isobars have different atomic numbers and the same mass number [33]

• Flashcard 91: How do isotopes and isobars compare with respect to chemical properties?

• Answer: Isotopes have similar chemical properties, while isobars have different chemical properties [33, 34]

• Flashcard 92: How do isotopes and isobars compare with respect to physical properties?

• Answer: Isotopes have different physical properties while isobars have similar physical properties [33, 34]

Flashcards on Key Concepts (Review)

• Flashcard 93: What is the key idea behind the "PG" in the mnemonic for remembering the scientists?

• Answer: P stands for Proton discovered by Goldstein [35]

• Flashcard 94: What does "T" represent in the scientist mnemonic?

• Answer: T stands for Thomson, discoverer of the electron (Tee) [35]

• Flashcard 95: What does "RG" represent in the scientist mnemonic?

• Answer: Rutherford and his Gold foil experiment [35]

• Flashcard 96: What was the key contribution of Bohr according to the mnemonic?

• Answer: He was like a father to Rutherford, correcting his mistakes [35, 36]

• Flashcard 97: What does the "no cheating" represent in the scientist mnemonic?

• Answer: Neutron discovery by Chadwick [36]

• Flashcard 98: Why are the outermost shells of atoms important?

• Answer: They determine the atom's chemical behaviour and valency [25, 26]

• Flashcard 99: In an atom, what is the role of the nucleus?

• Answer: It contains the protons and neutrons and holds the mass of the atom [12]

• Flashcard 100: Why is the concept of stability important for understanding the structure of the atom?

• Answer: Atoms want to be stable, and this is why they lose, gain, or share electrons and combine. Achieving the stable noble gas configuration is a key to understanding atomic behaviour. [25, 26]