"AKC SCIENCE CLASSES"
CLASS 09 TH (CBSE AND MP BOARD)
CHAPTER 04
STRUCTURE OF THE ATOM
INTEXT QUESTIONS AND ANSWERS
NCERT INTEXT QUESTIONS (PAGE NO. 42)
Q.01:- What are canal rays?
Ans:- Canal rays are also called anode rays, are seen moving from the anode towards the cathode in the specially designed tube. However, they do not originated from the anode.
Q.02:- If an atom contains one electron and one proton, will it carry any charge or not?
Ans:- No, it will not carry any charge because an electron has a unit negative charge and a proton has a unit positive charge. The neutralise each other.
NCERT INTEXT QUESTIONS (PAGE NO. 49)
Q.01:- On the basis of Thomson's model of an atom explain how the ato is neutral as a whole.
Ans:- According to Thomson's model of an atom, an atom may be regarded as a positively charged sphere in which protons are present. The negatively charged electrons are believed to be studded or embedded in the sphere. Since the negative charges due to electrons and positive charges due to protons balance each other, the atom as a whole is neutral.
Q.02:- On the basis of Rutherford's model of an atom, which sub-atomic particle is present in the nucleus of an atom?
Ans:- The nucleus of atom is positively charged according to Rutherford's model of an atom. All the protons in an atoms are therefore, present in the nucleus.
Q.03:- Draw a sketch of Bohr's model of an atom with three shells.
Ans:- Bohr's model of an atom which with three shells.
Ans:- If the metal is a heavy one like gold (e.g. silver, platinum etc.,) similar results will be obtained. However if the metal is quite light (e.g., sodium, magnesium etc.) it is just possible that the fast moving and massive 𝜶-particles (4u mass) may push the nucleus aside and pass through with slight deviations only.
Q.05:- Name the three sub-atomic particles in an atom.
Ans:- The sub-atomic particles in an atom are protons, electrons, and neutrons.
Q.06:- Helium atom has atomic mass of 4u and has two protons in its nucleus. How many neutrons does it have?
Ans:- Mass number of helium is equal to its atomic mass but has no units.
∴ Mass number (A) of helium = 4
No. of protons in the nucleus = 2
Atomic number (Z) of the element = 2
No. of neutrons (n) = A - Z = 4 - 2 = 2.
NCERT INTEXT QUESTIONS (PAGE NO. 50)
Q.01:- Write the distribution of electrons in carbon and sodium atoms.
Ans:- Carbon (Z = 6) : 2 (K-shell) ; 4(L-shell)
Sodium (Z = 11) : 2 (K-shell) ; 10 (L-shell) ; 1 (M-shell)
Q.02:- If the K and L shells of an atom are full, then what would be the number of electrons in the atom?
Ans:- Maximum no. of electrons in K-shell = 2
Maximum no. of electrons in L-shell = 8
Total no. of electrons in the atom = 2 + 8 = 10.
NCERT INTEXT QUESTIONS (PAGE NO. 52)
Q.01:- How will you find the valency of Chlorine, sulphur and magnesium?
Ans:- Atomic number of chlorine 17 and electronic configuration 2, 8, 7. So it has 7 electrons in the outermost shell and it requires 1 electron to complete the octet. So its valency is one.
Electronic configuration of sulphur (atomic number 16) is 2, 8, 6, so it require 2 electrons to complete the octet. So its valency is 2.
Electronic configuration of magnesium (atomic number 12) is 2, 8, 2. So it has to give two electrons, So its valency is two.
Q.02:- If number of electrons in an atom is 8 and number of protons is also 8, then
(ⅰ) What would be the atomic number of the atom?
(ⅱ) What is the charge on the atoms?
Ans:- (ⅰ) Atomic number (Z) of the atom
= No. of proton
= No of electrons = 8
(ⅱ) Charge on the atom = No. charge because number of electrons is equal to number of protons
Q.03:- With the help of Table 4.1, find out the mass number of oxygen and sulphur atom.
= 8 + 8 = 18
Mass number of sulphur = 16 + 16 = 32.
NCERT INTEXT QUESTIONS (PAGE NO. 53)
Q.01:- For the Symbol H, D and T tabulate three sub-atomic particles found in each of them.
Ans:-
Q.02:- Write down the electronic configuration of any one pair of isotopes and isobars.
Ans:- Isotopes of Chlorine :- ³⁵17Cl and ³⁷17Cl electronic configurations of both is 2, 8, 7.
Isobars :- ⁴⁰20Ca and ⁴⁰18Ar
⁴⁰18Ar : 2, 8, 8.
⁴⁰20Ca : 2, 8, 8, 2.
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