Electronic Configuration Based On Bohr's Model

When atoms react, it is actually the electrons that interact. For this reason, the arrangement of electrons is responsible for the structure of atom. The arrangement of electrons refers not only to the number of electrons that an atom possesses, but also their distribution around the nucleus.

According to Bohr's theory, the electron move in a specific circular orbit around the nucleus, much like the earth moves around the sun. These orbits are called energy levels or shells and are designated as K, L, M, N, O, P orbits and represented by 1, 2, 3, 4, 5, 6, starting from one nearest to the nucleus.

Therefore, K shell is the first shell, L shell is second shell, and M shell is the third shell, and so on. The maximum number of electrons in the given shell is -governed by the formula 2n2, where n is the number of orbits (shell or energy level). Thus first orbit can have a maximum of two electrons (n=l). The second orbit can have a maximum of eight electrons (n=2) and the third orbit can have a maximum of eighteen electrons (n=3) and so on.

The arrangement of electron in the first twenty elementsí_ the periodic table is as under:

 

Table 3.3 Shows the Arrangement of Electrons in the First 20 Elements.

 

Elements         Atomic                           Electrons in the Shells                   

                     Numbers                   K or 1st                 L or 2nd             M or 3rd     N or 4th

 

H                            1                  1                  -                  -                  -    

He                         2                  2

Li                           3                  2                  1                 -                  -

Be                          4                  2                  1                  -                  -

B                           5                  2                  3                  -                  -

C                            6                2                  4                  -                  -

N                            7                  2                  5                  -                  -

O                            8                  2                  6                  -                  -

F                            9                  2                  7                  -                  -

Ne                          10                2                  8                  -                  -

Na                          11                2                  8                  1                  -

Mg                          12                2                  8                  2

Al                           13                2                  8                  3

Si                           14                2                  8                  4                  -

P                            15                2                  8                  5

S                            16                2                  8                  6           

Cl                           17                2                  8                  7

Ar                           18                2                  8                  8

K                            19                2                  8                  8                  1

Ca                          20                2                  8                  8                  2

 

 

 
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