CHEMISTRY..STRUCTURE OF ATOM..Q&A

Q1 State Heisenberg Uncertainty Principle ?

Ans. It is impossible to determine the exact position & exact momentum or velocity of microscopic particle.

Q2-Write E.C. for Oxygen ?

Q3. Which orbital has quantum no(a) n= 3 & l=1 

(b) n= 2, l= 0  

Ans: (a)3p orbitals.  (b) 2s

Q4.Find the wave length of Yellow emission of sodium whose frequency 5.09 x 10

14

per sec ?

Ans:(hint: wave length = C/V0)

Q5. How was Neutron discovered? Write equation only?

Q6. Calculate the wave length of an electron whose KE is 3x 10

-25 J ?

Q7. An element with mass number 81 contains 31.7% more neutrons as compare to protons find out atomic symbol of element(Br)

Q8. What is threshold frequency? 

Ans –The minimum frequency required to eject out electron from an atom.

Q9.Write the draw back of Rutherford Atomic Model ?

Ans   (1). He was unable to explain the stability of Atom.

(2). He could not explain the line spectrum.

Q10.Give the points of Rutherford Model ?

Ans. 1. Atom is neutral.

2.Whole mass is concentrated in nucleus.

3.Electrons are revolving in orbits.

Q10-A 10 g Table Tennis Ball is moving with a speed of 90 m/s which is measured with an accuracy of 4% find out uncertainty in it speed as well as position.

Ans:

m = 10g

m = 0.01kg

∆v = 4% of 90 m/s

= 3.6 m/s

∆x = h/4π m∆v

Put the values

=1.46 x 10

-33

m

Q.11 How many electrons with  l=2 are there in an atom having atomic number 54 ?

Ans. 3d

10 

& 4d

10 

= 20.

Q. What is electronic configuration of Cu (z=29) and Cr (z=24) by aufbau principle?

Q.Define Pauli’s exclusion principle ?  

Ans. No two electrons in an atom can have same set ofall four quantum numbers. If three are same one Quantum number must have different value.         

Q.Define Aufbau Principle. Give a Suitable example ?

Q. a) Where is the probability of finding an electron is zero?  

b) How many maximum electrons can be found in 3d orbital with spin quantum

number -1/2? 

c) Which quantum no. determines the orientation of the orbital? 

Ans.a) at Node.                

b) 5-electrons.

c) magnetic quantum no

Q. Why is s-orbital orbital considered non directional while p-orbital directional?

Ans. Electron density in s-orbital is equal in all direction while it dumble shaped along one axis in p-orbitals.

Q4.Which of the following can exhibit maximum Para magnetism: Ca, Fe

+2

,Cu

+2

?

Ans.Fe

2+ 

due to presence of 4 unpaired electrons in 3d orbitals.  

Q..What will be the increasing order of energy of 2s, 3s, 3d, 4f in atom? 

Ans. 2s< 3s < 3d < 4f 

Q.Is the energy of an electron in 2s orbital same as of that in 2p orbital? Why? 

Ans. No, the energy depends upon (n+l) values in an atom. Hence 2p orbital has greater energy than 

2s

Q.“In reality all the s-orbitals are spherically symmetric.” What does this represent?

Ans. The probable density of an electron in s-orbital is equally distributed at all coordinates in space. 

Q.3  Give three differences between orbit and orbital.

Ans

ORBIT                                                                                             

1 It is a well defined circular path around the 

nucleus in which electron move .

 2 Maximum no. of electrons in an orbit is 

2n

2

. 

3.  Do not have directional characteristics.     

  ORBITAL           

 1 It is a 3dimensional region around the nucleus where 

the probability of finding electron is 

maximum.  

2 Maximum 2 electrons in an orbital.

3. Except s all have directional characteristics

QExplain the significance of Azimuthal quantum number ?

Ans. It refers as sub-energy level of an atom.

Q. How many of the following are possible: 1p, 2s, 3p, 3f, 3d. ?

Ans.2s , 3p & 3d are possible.

Q. n = 3, l = 3, m

l 

= -3, ms

= +1/2. Is the given set of quantum numbers possible? If not, explain by 

giving reasons. 

Ans. It is not possible because 3f does not exist in an atom

Q.Explain why half-filled orbitals have extra stability ?

Ans. It has symmetrical electron density as well as greater exchange energy.

Q. Explain the significance of spin quantum number ?

Ans.The direction of spinning of an electron in an orbit as well as the net magnetic moment of an orbital.

Q..   What will be the value of n & l of the followings? (L1)

1.  4s

1

2.  5d

1

3.  4f

1

Q.  What is Hund’s rule of maximum multiplicity? What is its significance?

Ans Pairing of electrons in an orbital takes place only when all orbitals of same sub-shell become singly occupied. It helps to equalize energy of a sub-shell