NEET Physics Chapter 4 Structure Of Atom Question And Answers

NEET Physics Chapter 4 Structure Of Atom Question And Answers

Question 1. Define atomic number.
Answer.

Atomic Number:

The atomic number is the number of protons in an atom of an element.

Question 2. Define atomic mass.
Answer.

Atomic Mass:

The atomic weight measures the total number of particles present in an atom’s nucleus. The nucleus is made up of protons and neutrons. So,

Mass number = (Number of Protons) + (Number of Neutrons)

Question 3. What are canal rays?
Answer.

Canal Rays:

These positively charged radiations are produced in discharge tubes from the anode called canal rays.

Question 4. What is the relative mass of a neutron?
Answer.

Relative mass of neutron:

A neutron is 1842 times heavier than an electron.

Question 5. Define nucleon.
Answer.

Nucleon:

A nucleon is a sub-atomic particle found in the nucleus of an atom.

Question 6. What are the limitations of Thomson’s plum pudding model?
Answer.

The limitations of Thomson’s plum pudding model:

• Thomson’s plum pudding model: could not explain the result of the scattering experiment performed by Rutherford.
• Thomson’s plum pudding model: did not give any experimental evidence in its support.

Question 7. What are the observations of Rutherford’s model?
Answer.

Observations of Rutherford’s Model were:

• Most of the alpha particles pass through the foil without getting deflected, which means that most of the space inside the atom is empty.
• Some of the alpha particles were deflected by a small angle, which means that the positive charge ofthe atom occupies very little space.
• Some of the alpha particles rebound back, which means the entire positive charge and mass of the atom are concentrated in a very small volume inside an atom.

Question 8. What are the limitations of the Rutherford model?
Answer.

The limitations of Rutherford’s model were:

• Rutherford proposed that the electrons revolve around the nucleus in fixed paths called orbits. But according to Maxwell, an accelerated charged particle such as an electron always emits electromagnetic radiation and this radiation would carry energy from the motion of the electron which would come at the cost of shrinking of orbits. So, the electrons would collapse in the nucleus.
• Rutherford did not say anything about the arrangement of electrons in an atom.

Question 9. Define electronic configuration.
Answer.

Electronic configuration:

The electronic configuration is an arrangement of electrons in various shells of an atom of the element.

Question 10. Explain the symbol ¹⁶O₈.
Answer.

Symbol ¹⁶O₈

It shows that oxygen has a mass number of 16 and an atomic number is 8.

Question 11. Draw the electron dot structure of Chlorine (atomic number 17).
Answer.

The electron dot structure of Chlorine (atomic number 17):

Chlorine (Cl) –2, 8, 7

Question 12. How can an atom obtain a stable configuration?
Answer.

Atom can obtain a stable configuration, either by:

• Losing an electron
• Gaining an electron
• Sharing an electron

Question 13. What are valence electrons?
Answer.

Valence electrons:

Valence electrons are the electrons present in the outermost orbit of an atom, thus determining the valency of an atom.

Question 14. Why does Magnesium ion exist as Mg²⁺?
Answer.

Magnesium ion exists as Mg^2+.

Magnesium molecule has an electronic configuration 2,8,2. It has two electrons in its outermost orbit, so it requires six more electrons to complete its outermost orbit (M-shell). So, it will either donate its two electrons to another atom or share electrons from another atom just to complete its octet. Master your Test

Question 15. What approximation is taken while calculating the number of neutrons?
Answer.

Protons and neutrons have approximately the same mass and the mass defect of nucleon binding is small as compared to the nucleon mass, the atomic mass of any atom. This approximation of mass is used to calculate the number of neutrons in an element.

Question 16. The atomic number of calcium is 20. Calculate the number of electrons and protons in calcium.
Answer.

Given

An atomic number of calcium is 20.

Since, Atomic number = Number of protons = Number of electrons So, the number of electrons in calcium is = the 20Number of protons in calcium = 20

Question 17. The atomic mass of aluminum is 27 u and the atomic number is 13, find the number of protons and neutrons in aluminum.
Answer.

Given

The atomic mass of aluminium is 27 u and the atomic number is 13

Atomic number = 13

So, the number of protons = 13

Atomic mass (Mass number) = Number of protons + Number of neutrons

Let the number of neutrons be ‘n’

27 u = 13 + n

n = 27 − 13 = 14

So, number of proton = 13 and number of neutron = 14

Question 18. Define isotopes.
Answer.

Isotopes:

Isotopes are the atoms having same number of protons, but different numbers of neutrons, i.e., they have different atomic weights.

Question 19. List 3 applications of isotopes.
Answer.

Applications are:

• The identification of primary and secondary food sources.
• Tracing nutrient and mineral uptake by plants and animals.
• Determining the relative importance of plants and microbes to greenhouse gas emissions from soil.

Question 20. Why do radioactive elements have unstable nuclei?
Answer.

It has an unstable combination of protons and neutrons, and that is why they have an unstable nucleus.