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EDUGUIDE
KALYANPUR,KHOWAI,TRIPURA
CONTACT NO: 7642028468
(AJAY ROY)
Class: ix, Science
Structure of the atom
One Mark questions:
Q: What is an atom?
A: An atom is the smallest unit of matter that retains the chemical properties of an element.
Q: What is the nucleus of an atom?
A: The nucleus is the central part of an atom, consisting of protons and neutrons.
Q: Who is credited with the discovery of the electron?
A: J.J. Thomson is credited with the discovery of the electron.
Q: What is the charge of an electron?
A: The charge of an electron is negative (-1).
Q: Who proposed the planetary model of the atom?
A: Niels Bohr proposed the planetary model of the atom.
Q: What is the charge of a proton?
A: The charge of a proton is positive (+1).
Q: Who discovered the proton?
A: Ernest Rutherford discovered the proton.
Q: What is the mass of a neutron?
A: The mass of a neutron is approximately 1 amu (atomic mass unit).
Q: What is an isotope?
A: Isotopes are atoms of the same element with the same number of protons but a different
number of neutrons.
Q: What is an ion?
A: An ion is an atom or molecule that has gained or lost one or more electrons, resulting in a
charged species.
Q: What is the atomic number of an element?
A: The atomic number is the number of protons in the nucleus of an atom.
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Q: What is the mass number of an atom?A: The mass number is the total number of protons
and neutrons in an atom.
Q: What is the electron configuration of an atom?
A: The electron configuration refers to the arrangement of electrons in the orbitals of an
atom.
Q: What is the fundamental particle of an atom?
A: The fundamental particles of an atom are electrons, protons, and neutrons.
Q: What is the charge of a neutron?
A: A neutron has no charge, it is neutral.
Q: What are the three subatomic particles of an atom?
A: The three subatomic particles of an atom are protons, neutrons, and electrons.
Q: Who discovered the neutron?
A: James Chadwick discovered the neutron.
Q: What is the relation between atomic number and the number of protons in an atom?
A: The atomic number is equal to the number of protons in an atom.
Q: What is the principal quantum number?
A: The principal quantum number (n) defines the energy level or shell of an electron in an
atom.
Q: What is the significance of Rutherford's gold foil experiment?
A: It led to the discovery of the atomic nucleus.
Discoveries:
Q: What did Bohr's model explain about the atom?
A: Bohr's model explained the quantized orbits of electrons and the stability of atoms.
Q: In Rutherford's experiment, what did the deflection of alpha particles indicate?
A: It indicated the presence of a small, dense, positively charged nucleus at the center of the
atom.
Q: What was the main conclusion of Thomson's cathode ray tube experiment?
A: The experiment led to the discovery of the electron.
Q: What did Millikan's oil drop experiment measure?
A: It measured the charge of an electron.
Q: Who proposed the concept of electron shells or energy levels?
A: Niels Bohr proposed the concept of electron shells.
Q: What was the main observation in the gold foil experiment?
A: Some alpha particles were deflected at large angles, indicating the presence of a dense
nucleus.
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Q: What is the concept of orbitals in an atom?
A: Orbitals are regions around the nucleus where there is a high probability of finding an
electron.
Q: What did Rutherford's experiment show about the size of the nucleus?
A: The nucleus is very small compared to the overall size of the atom.
Q: What was the main finding of Bohr's model?
A: Electrons move in discrete orbits around the nucleus without emitting energy.
Q: What is the significance of the quantum mechanical model of the atom?
A: It explains the behavior of electrons in terms of probabilities, not definite paths.
Numerical Aspects:
Q: Calculate the number of protons in an atom of carbon-12.
A: The number of protons in carbon-12 is 6.
Q: How many electrons are in a neutral atom of sodium (Na)?
A: A neutral sodium atom has 11 electrons.
Q: An atom has an atomic number of 16 and a mass number of 32. How many neutrons
does it have?
A: The number of neutrons is 32 - 16 = 16.
Q: What is the mass number of an isotope of hydrogen with 1 proton and 2 neutrons?
A: The mass number is 1 + 2 = 3.
Q: How many electrons can the 2nd energy shell hold?
A: The 2nd energy shell can hold a maximum of 8 electrons.
Q: What is the atomic number of an element with 13 protons?
A: The atomic number is 13.
Q: If an atom has 8 protons, 8 neutrons, and 8 electrons, what is its mass number?
A: The mass number is 8 + 8 = 16.
Q: An element has 17 protons, 18 neutrons, and 17 electrons. What is its mass number?
A: The mass number is 17 + 18 = 35.
Q: If an atom of oxygen has 8 protons and 8 electrons, what is its atomic number?
A: The atomic number is 8.
Q: What is the number of electrons in an atom of calcium (Ca) with atomic number 20?
A: The number of electrons in calcium is 20.
Q: How many neutrons are in an atom of chlorine-35 (Cl)?
A: Chlorine-35 has 35 - 17 = 18 neutrons.
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Q: If an atom has 6 electrons and 6 protons, what is its charge?
A: The atom is neutral.
Q: How many protons are in a neutral atom of iodine?
A: The atomic number of iodine is 53, so it has 53 protons.
Q: What is the number of electrons in an atom of magnesium (Mg)?
A: Magnesium has 12 electrons.
Q: How many protons and electrons are in a neutral atom of sulfur?
A: A neutral sulfur atom has 16 protons and 16 electrons.
Q: Calculate the number of neutrons in an atom of nitrogen-14.
A: Nitrogen-14 has 14 - 7 = 7 neutrons.
Q: What is the maximum number of electrons that can occupy the 3rd shell of an atom?
A: The maximum number of electrons that can occupy the 3rd shell is 18.
Q: What is the mass number of an isotope of carbon with 6 protons and 8 neutrons?
A: The mass number is 6 + 8 = 14.
Q: An atom has an atomic number of 6 and a mass number of 14. How many neutrons does
it have?
A: The number of neutrons is 14 - 6 = 8.
Q: If an atom has 20 protons, how many electrons does a neutral atom of calcium have?
A: A neutral calcium atom has 20 electrons.
