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STRUCTURE OF ATOM 

Important Questions

1. Write the postulates of Bohr's Atomic model and mention its limitations.

A: Postulates:

Electrons in an atom occupy stationary orbits of fixed energy at different distances from the nucleus.

When an electron jumps from a lower energy state (ground state) to higher energy states (excited state) it absorbs energy or emits energy when such a jump occurs from a higher energy state to a lower energy state.

The energies of an electron in an atom can have only certain values E1, E2, E3, ........... that is, the energy is quantized. The states corresponding to these energies are called stationary states and the possible values of the energy are called energy levels.

When electron reaches to ground state from excited state, it loses energy and seen in the form of electromagnetic energy and the wavelength.

Bohr's model explains all the line spectra observed in the case of Hydrogen atom.

Limitations:

Bohr's model failed to account for the atomic spectra of atoms if more than one electron.

Bohr's model failed to account for splitting of line spectra.
 

2. Explain Bohr - Sommerfeld model of an atom.
A:

In an attempt to account for the splitting of line spectra, Sommerfeld modifies Bohr's model by adding elliptical orbits.

While retaining the first of Bohr's circular orbits as such he added one elliptical orbit to Bohr's second orbit, two elliptical orbits to Bohr's third orbit etc. Such that the nucleus of the atom is one of the principle Foci of these elliptical orbits.

He was guided by the fact that, in general, periodic motion under the influence of a central force will lead to elliptical orbits with the force situated at one of the Foci.

Limitations:

This model failed to account for the atomic spectra of atoms of more than one electron.

3. Explain how does the quantum numbers be useful to understand atomic structure.

A: The quantum numbers describe the space around the nucleus where the electrons are found and also their energies.

Principal quantum number (n):

The principal quantum number is related to the size and energy of the main shell.

'n' has positive integer values of 1, 2, 3, .......

'n' increases, the shells become larger and the electron in those shells are farther from the nucleus.

An increase in 'n' also means higher energy. n = 1, 2, 3, ....... are often represented by the letters K, L, M, ........... for each 'n' value there is one main

he angular - momenum quantum number (l):

'l' has integer values from 0 to n - 1 for each value of 'n' each 'l' value represents one sub-shell.

Each value of 'l' is related to the shape of a particular sub-shell in the space around the nucleus.

The value of 'l' for a particular sub-shell is generally designated by the letters s, p, d, ... as follows

       l = 0 means s orbital
       l = 1 means p orbital
       l = 2 means d orbital
       l = 3 means f orbital
The magnetic quantum number (ml):
The magnetic quantum number (ml) has integer values between -l and +l, including zero.
Thus for a certain value of l, there are (2l + 1) integer values of ml as follows -l, (-l  + 1), ....., -1,  0,  1, ...... (+l  -1),  + l
These values describe the orientation of the orbital in space relative to the other orbitals in the atom.
Spin quantum number (ms):
This quantum number refers to the two possible orientations of the spin of an electron, one clock wise direction (+ ) and the other anti - clock wise direction (- )

 

4. Compare orbit and orbital.                                                                                   (AS 1) 4 Marks
A:

5. Explain the principles used to explain the electronic configuration with one example each. (AS 1)                                                                                                                                    4 Marks
                                                                         (or)
What are the rules to be followed while filling the electrons in atoms which contains more than one electron? How do you fill the electrons in degenerate orbitals? Explain. (AS 1) 4 Marks
A: Paulis Exclusion Principle: No two electrons of the same atom can have all the four quantum numbers same.
     If n, and ml are the same for two electrons then ms must be different. In the Helium atom the spins must be paired. 
     Electrons with paired spins are denoted by '↑↓' one electron has ms = + and the other has ms = -. They have anti parallel spins. So electronic configuration of Helium atom is 
                                                                                                                                                      1s2
The set of four quantum numbers is

 

n

l

ml

ms

I electron

1

0

0

II electron

1

0

0

Aufbau Principle: In the ground state the electronic configuration can be build up by placing electrons in the lowest available orbitals until the total number of electrons added is equal to the atomic number. This is called Aufbau principle.
      Thus orbitals are filled in the order of increasing energy. Electrons are assigned to orbitals in order of increasing value of (n + l).
      For sub-shells with the same value of (n + l), electrons are assigned first to the sub-shell with lower 'n'.
    Ascending order of energies of various atomic orbitals is given below
1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p < 6s ...........
e.g.:    H (Z = 1)           Li (Z = 3)  
                             1s1                             1s2 2s1
        He (Z = 1)    
                               1s2 
Hund's Rule: Electron pairing in orbitals starts only when all empty orbitals of the same energy (degenerate orbitals) are singly occupied.
e.g.: The configuration of Carbon atom (Z = 6) is 1s1 2s2 2p2.

 The first four electrons go into 1s and 2s orbitals. The next two electrons go into separate 2p orbitals, with both electrons having the same spin.
                        
6. Draw the shapes of s and p orbitals. (AS 5)                                                                 4 Marks
A: The shape of s - orbital is spherical.
     
         s - orbital
The shape of p - orbital is dumbbell.
      
       px - orbital                 p- orbital                  p- orbital


7. Draw the shapes of d - orbitals. (AS 5)                                                                         4 Marks
A: The shape of d - orbital is double dumbbell.

 

8. Draw the figure showing the increasing values of (n + l). (AS 5)                              2 Marks
A:                   = 0 = 1 = 2 = 3
   

9. Draw a figure of electromagnetic wave and label the parts. (AS 5)                         2 Marks
A:
    

10. Draw a figure showing sub - energy levels of fourth energy level (n = 4) of Sommerfeld's model and state the values of 'l' and 'n'. (AS 5)                                                                2 Marks
A:
            

11. Give an example of visible spectrum in nature. Explain what is a visible spectrum.
(AS 1, AS 6)                                                                                                                          2 Marks
A: The familiar example of the visible spectrum in nature is the formation of a rainbow. Each colour in a rainbow is characterised by a specified wavelength from red (higher wavelength) to violet (shorter wavelength).
       These colours (wavelengths), that the human nacked eye is sensitive to, are called visible light. The range of wavelengths covering red colour to violet colour is called the visible spectrum.


12. The electronic configuration of an atom is as follows. (AS 4)                                   2 Marks
        
i) Which elements atom is it?
A: Carbon
ii) Which orbital is the last electron is?
A: 2p orbital.
iii) When excited what could be the number of single electrons in this atom.
A: In excited state the electron in 2s orbital enters into 2p orbital. So, it has 4 unpaired electrons.
iv) What is the value of principal quantum numbers of two electrons in the first box?
A: The value of principal quantum number is 1.

13. i) An electron in an atom has the following set of four quantum numbers to which orbital is belong to. (AS 4)                                                                                                              2 Marks

n

l

ml

ms

3

0

0

+ 

A: This electron belongs to 3s orbital. Spin is in clockwise direction  3s1.

ii) Write the four quantum numbers for 2s1 electron.
A: The four quantum numbers for 2s1 electron are

n

l

ml

ms

2

0

0

+ 


14. Which rule is violated in the electronic configuration 1s2 2s2 2p6 3s2 3p6 4s0 3d1 and how? (AS 1)                                                                                                                          2 Marks
A: It violated Aufbau's principle. After filling '3p' orbital, two orbitals 3d and 4s are available for the newly coming electron. But, the energy of '3d' orbital (n + = 3 + 2 = 5) is greater than that of 4s orbital (n + = 4 + 0 = 4). But, as per the Aufbau's principle, electron occupies the orbital with lowest energy first. Hence, the electronic configuration is 1s2 2s2 2p6 3s2 3p6 4s1.

15. Which principle is not followed in writing the following electronic configuration? Give reasons. 1s2 2s1 2p2. (AS 1)                                                                                               1 Mark
A: The principle violated here is Aufbau principle, we have to fill electrons in 2s before going to 2p.


16. Which rule is violated in the following electronic configuration ? (AS 1 )                1 Mark
         
A:
 The rule violated in the given electronic configuration is Hund's rule.

17. Write electronic configuration of following elements. (AS 1)                                     1 Marks
a) Lithium b) Boron
A: a) Lithium (Z = 3) 1s2 2s1   
b) Boron (Z = 5) 1s2 2s2 2p1    

18. What is the use of line spectra? (AS 6)                                                                         1 Mark
A: The lines in atomic spectra can be used to identify unknown atoms, just like finger prints are used to identify people.


Short Answer Questions

1. Which of the colour in visible light have more wavelength ? (AS1) 1 Mark
A: Red Light

 

2. Which of the colour in visible light have higher frequency? (AS1) 1 Mark
A: Violet

3. In Electromagnetic spectrum, which rays has higher wavelength? (AS1) 1 Mark
A: Radio Waves

4. Which of the Electromagnetic rays will have shorter wavelength?
A: γ - rays

5. What will be the wavelength range of visible spectrum? (AS1) 1 Mark
A: 400 nm to 700 nm

6. In E = hν, what is the value of Planck's constant (h) value ? (AS1) 1 Mark
A: h = 6.625 × 10-34 J-s

7. Which colour is exhibited by cupric chloride on flame test? (AS3) 1 Mark
A: Green Colour


8. Which coloured light is produced by sodium vapours in street light? (AS1) 1 Mark
A: Yellow Colour

9. What happens when electron gains energy? (AS2) 1 Mark
A: Electron jumps from lower energy level to higher energy level.

10. In which form electron can gain or lose the energy? (AS1) 1 Mark
A: In the form of Electromagnetic radiation.

11. Who introduced elliptical orbits? (AS1) 1 Mark
A: Sommerfeld.

12. Draw Bohr - Sommerfeld model of an atom when n = 2. (AS5) 1 Mark
A:
       

13. How Bohr - Sommerfeld justified the existance of elliptical orbits in Hydrogen spectrum?
                                                                                                                                 (AS1) 2 Marks
A: Splitting of line spectrum into fine spectral lines can show the existance of elliptical orbits along with circular orbits.
e.g.: n = 3, = 0, 1, 2

  
14. Who introduced Quantum mechanical model of atom? (AS1) 1 Mark
A: Erwin Schrodinger

15. What do you call the region of space around the nucleus where the probability of finding electron is maximum? (AS1) 1 Mark
A: Orbital

16. Which quantum number can explain the space orientation of the orbital? (AS1) 1 Mark
A: Space orientation of the orbital is explained by Magnetic Quantum number.

17. Which Quantum number can explain the size and energy of the main orbit?  (AS1) 1 Mark
A: Principal Quantum number

18. When n = 3, What are the values? (AS1) 1 Mark
A: n = 3, = 0, 1, 2

19. If = 3, What are the mvalues? (AS1) 1 Mark
A: = 3, ml = -3, -2, -1, 0, +1, +2, +3

20. What are four quantum numbers for the differentiating electron of Aluminium?  (AS1) 2 Marks
    A= 1s2 2s2 2p6 3s3p1
A:

21. Quantum no's of an electron in outermost orbit of an atom are given below.

Configuration - 1s2s2 2p6 3s2 3p3
(a) What is the outermost orbit of the shell? (AS4) 2 Marks
A: 3
(b) Write the Electronic configuration of the element.
A: 1s2 2s2 2p6 3s2 3p3
(c) What is atomic number of the element?
A: 15
(d) What is the valency of the element?
A: 5
22. Show the shape of p - orbitals. (AS1) 1 Mark
A: Dumbel shape     

23. Write the types of d-orbitals? (AS1) 2 Marks



24. Imagine, why 4s orbital of calcium filled before 3d - orbital? (AS2) 2 Marks
A: As per Aafbou principle the energy of 4s - orbital is less than 3d - orbital, so
    4s orbital is filled before 3d - orbitals.
    Energy of 4s orbital = n + = 4 + 0 = 4
    Energy of 3d orbital = n + = 3 + 2 = 5

25. Explain Pauli's exclusion principle by constructing a table for Lithium element? (AS1) 2 Marks
A: Li = 1s2 2s1

26. In the following orbital diagram, which principle is violated? (AS1) 1 Mark

            
A: Hund's rule is violated.

27. Which rule is violated in the electronic configurtion 1s0 2s2? (AS1) 1 Mark
A: Aufbau principle.

28. What is the electronic configuration of Potassium element? (AS1) 1 Mark
A: Atomic Number of K = 19
     1s2 2s2 2p6 3s2 3p6 4s1

29. Draw Bohr - Sommerfeld model of an atom when n = 4. (AS5) 2 Marks
A:
      

Posted Date : 02-10-2021

గమనిక : ప్రతిభ.ఈనాడు.నెట్‌లో కనిపించే వ్యాపార ప్రకటనలు వివిధ దేశాల్లోని వ్యాపారులు, సంస్థల నుంచి వస్తాయి. మరి కొన్ని ప్రకటనలు పాఠకుల అభిరుచి మేరకు కృత్రిమ మేధస్సు సాంకేతికత సాయంతో ప్రదర్శితమవుతుంటాయి. ఆ ప్రకటనల్లోని ఉత్పత్తులను లేదా సేవలను పాఠకులు స్వయంగా విచారించుకొని, జాగ్రత్తగా పరిశీలించి కొనుక్కోవాలి లేదా వినియోగించుకోవాలి. వాటి నాణ్యత లేదా లోపాలతో ఈనాడు యాజమాన్యానికి ఎలాంటి సంబంధం లేదు. ఈ విషయంలో ఉత్తర ప్రత్యుత్తరాలకు, ఈ-మెయిల్స్ కి, ఇంకా ఇతర రూపాల్లో సమాచార మార్పిడికి తావు లేదు. ఫిర్యాదులు స్వీకరించడం కుదరదు. పాఠకులు గమనించి, సహకరించాలని మనవి.

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