# Structure of the Atom

Structure of the Atom - NCERT Guide Science Class 9

Q1: Compare the properties of electrons, protons and neutrons.

Q2: What are the limitations of J.J. Thomson’s model of the atom?
Q3: What are the limitations of Rutherford’s model of atom?
Q4: Describe Bohr’s model of atom.
Q5: Compare all the proposed models of an atom given in this chapter.

Q6: Summarize the rules for writing of distribution of electrons in various shells for the first eighteen elements.
Q7: Define valency by taking examples of silicon and oxygen.
Q8: Explain with examples (i) Atomic number, (ii) Mass number, (iii) Isotopes and (iv) Isobars. Give any two uses of isotopes.
Q9: Na+ has completely filled K and L shells. Explain.
Q10: If bromine atom is available in the form of, say, two isotopes7935Br (49.7%) and 8135Br (50.3%), calculate the average atomic mass of bromine atom.
Q11: The average atomic mass of a sample of an element X is 16.2 u.What are the percentages of isotopes 168X and 188X in the sample?
Q12: If Z=3, what would be the valency of the element? Also name the element.
Q13: Composition of the nuclei of two atomic species X and Y are given as under
X Y
Protons = 6 6
Neutrons = 6 8
Give the mass numbers of X and Y. What is the relation between the two species?
Q14: For the following statements, write T for True and F for False.
1. JJ Thomson proposed that the nucleus of an atom contains only nucleons.
2. A neutron is formed by an electron and a proton combining together. Therefore, it is neutral.
3. The mass of an electron is about 1/2000 times that of proton
4. An isotope of iodine is used for making tincture iodine, which is used as a medicine.
Q15: Put tick (√) against correct choice and cross (X) against wrong choice in the following questions:

Rutherford’s alpha-particle scattering experiment was responsible for the discovery of

1. Atomic Nucleus
2. Electron
3. Proton
4. Neutron
Q16: Put tick (√) against correct choice and cross (X) against wrong choice in the following questions:

Isotopes of an element have

1. the same physical properties
2. different chemical properties
3. different number of neutrons
4. different atomic numbers.
Q17: Put tick (√) against correct choice and cross (X) against wrong choice in the following questions:

Number of valence electrons in Cl– ion is:

1. 16
2. 8
3. 17
4. 18