Class 10 Physics Important practice questions with solutions

 Class 10 Physics Important practice questions with solutions.

Q.  The four quantum number values of the 21st electron of Scandium(Sc) are given in the following table.

 Write the values of the four quantum numbers for the 20th electron of Scandium(Sc) in the form of the table.                                                                 (TS SSC Exam March 2017)

Sol:-

• Atomic number of the Scandium(Sc) Z=21
• Electronic configuration of the Scandium(Sc) - 1s2, 2s2, 2p6, 3s2, 3p6, 4s2, 3d1
• 21st electron of Scandium(Sc) is filled in 3d orbital and it is denoted as 3d1
• 20th electron of Scandium(Sc) is filled in the 4s orbital.  The second electron in 4s orbital is considered as the 20th electron.  
• 20th electron is 4s2 (2nd electron in 4s)

Four quantum numbers of the 20th (4s2) electron are:

• Principal quantum number n=4 (Main Shell of 4s orbital, here 4 is main shell in 4s)
• Angular Momentum quantum number l=0 (Angular momentum quantum number depends on the Principal quantum number.  For any 'n' value 'l' values are from '0' to maximum 'n-1'.  Here n=4. So, l values are l=0, 1, 2, 3.  Always l=0 for 's' orbital, l=1 for 'p' orbital, l=2 for 'd' orbital and l=3 for 'f' orbital and so on...)
• The 20th electron is filled in 's' orbital due to this it's Angular momentum number is '0'.

• Magnetic quantum number ml=0   [Magnetic quantum number depends on The Angular momentum quantum number for any 'l' value the total 'ml' values are equal to (2l+1) and these values start from -l and ends with +l (-l......0.......+l).  For example if l=2 (d orbital) ml values are (2x2+1) total 5 values will be there and these values start from -2 and end with +2. The five ml values are -2, -1, 0, +1, +2. But here l value is 0. So, only one ml value is there for 4s orbital and it is 0.]

• Spin quantum number ms= -1/2 [Spin quantum number mainly explains the orientation of electrons in the orbital. Only two electrons can be filled in each orbital.  So, two Spin quantum numbers only exist, the first value is +1/2 and the second value is -1/2.  The 20th electron of the Scandium is the 2nd electron of the 4s orbital, 19th electron of the Scandium is the first electron of the 4s orbital and it's spin is +1/2. The 20th electron of the Scandium is the second electron of the 4s orbital and it's spin is -1/2.]

The final answer is: