Page 1 - 3. LESSON NOTES-(BOHR BURRY SCHEME,DISTRIBUTION OF ELECTRONS IN VARIOUS SHELLS)

SAI International School
Lesson Notes

Subject-Chemistry
Ch-Structure of atom
Topic- Bohr Burry scheme, Distribution of electrons in various

shells
To be done in CW Copy
Recapitulation

Atomic Number: The total number of protons in the nucleus of an atom gives us the
atomic number of that atom. The atomic number of an atom is equal to the number
of protons in the nucleus of an atom or the number of electrons in an electrically
neutral atom.
Atomic number = Number of protons= Number of electrons
Z = p = e
Mass Number: The number of protons and neutrons combined to give us the mass
number of an atom.
Atomic mass number or mass number = Number of protons + Number of neutrons
A = p + n
Bohr bury scheme: The distribution of electrons in different orbits or shells is
governed by a scheme known as Bohr bury scheme. The arrangement of electrons
in various energy levels of an atom is known as Electronic configuration of an
atom. According to this scheme.
1. The electrons are arranged around the nucleus in different energy
levels/orbits which are named as K, L, M, N……. The electrons first occupy
the shell with lowest energy I.e., closest to the nucleus K Shell.
2. The maximum number of electrons present in the shell is given by the formula
2
(2 n ), where n is the orbit number or shell number. K=1, L=2, M=3……….
 The maximum numbers of electrons in different shells are as follows:
2
 The first orbit or K shell will have 2 × 1 = 2 electrons.
2
 The second shell or L shell will have 2 × 2 = 8 electrons.
 The third shell or M shell will have 2 × 3 = 18 electrons.
2
2
 The fourth shell or M shell will have 2 × 4 = 32 electrons and so on.
3. The last shell or outermost shell or Valance shell can accommodate maximum
8 electrons irrespective of its capacity.
e.g. M shell, the capacity is 18 but if it is the outermost shell then it can
accommodate maximum 8 electrons.
Electronic configuration of Hydrogen
Atomic number of hydrogen = 1
Therefore number of electrons = 1
st
Maximum number of electrons in 1 orbit = 2
st
Since, hydrogen has only one electron, therefore, it will reside in 1 orbit.

Thus electronic configuration of hydrogen
Number of orbit present in hydrogen = 1

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