Pauli's Exclusion Principle.pptx

Quantum Numbers, Electrons, Quantum State, Principal Quantum Number, Orbital Quantum Number

1. Pauli’s Exclusion Principle Dr.M.Sankareswari Assistant Professor of Physics VVVanniaperumal College for Women Virudhunagar

2. Pauli’s Exclusion Principle Statement: No two electrons in an atom exist in the same quantum state. The state of an electron can be completely determined by four quantum numbers n, l, m l , m s. “No two electrons in an isolated atom may have the same four quantum numbers” Explanation If two electrons of an atom have identical quantum numbers (n, l, m l , m s ), then one of those electrons would be excluded from entering into the constitution of the atom. Hence it is called as “ exclusion principle ”.

3. Pauli’s Exclusion Principle Application: This principle enables us to calculate the number of electrons in a subshell. Consider the K-shell with n = 1, l = 0 hence m l = 0. Since S = ½ ; m s can be either +1/2 or -1/2.Hence K shell can have 2 electrons; one electron with quantum numbers n = 1, l = 0, m l = 0, m s = +1/2 and another electron with quantum numbers n = 1, l = 0, m l = 0, m s = -1/2 K-shell is completed with 2 electrons.

4. Pauli’s Exclusion Principle 2) Consider the L-shell with n = 2, l = 0 or 1. For l = 0, m l = 0 , m s can be either +1/2 or - 1/2. There are two electrons in this sub shell. With n = 2, l = 1, m l = -1, 0, +1. For each of these m l value, m s can be either +1/2 or -1/2. There are six electrons in this sub shell . Hence L-shell is completed with 8 electrons.

5. Pauli’s Exclusion Principle 3) Consider the M-shell with n = 3, l = 0, 1, 2. For l = 0, m l = 0 , m s can be either +1/2 or - 1/2. There are two electrons in this sub shell. With n = 3, l = 1, m l = -1, 0, +1. For each of these m l value, m s can be either +1/2 or -1/2. There are six electrons in this sub shell . With n = 3, l = 2, m l = -2, -1, 0, + 1, +2. For each of these m l value, m s can be either +1/2 or -1/2. There are ten electrons in this sub shell. Hence M-shell is completed with 18 electrons.

6. Pauli’s Exclusion Principle 3) Consider the N-shell with n = 4, l = 0, 1, 2, 3. For l = 0, m l = 0 , m s can be either +1/2 or - 1/2. There are two electrons in this sub shell. With n = 4, l = 1, m l = -1, 0, +1. For each of these m l value, m s can be either +1/2 or -1/2. There are six electrons in this sub shell . With n = 4, l = 2, m l = -2, -1, 0, + 1, +2. For each of these m l value, m s can be either +1/2 or -1/2. There are ten electrons in this sub shell . With n = 4, l = 3, m l = -3, -2 , -1, 0, +1, + 2, +3. For each of these m l value, m s can be either +1/2 or -1/2. There are fourteen electrons in this sub shell. Hence M-shell is completed with 18 electrons.

7. Pauli’s Exclusion Principle Conclusions: The maximum number of electrons in a sub-shell with a given value of l is 2(2l + 1). The sub shells are denoted by s, p, d, f, g --- The number of electrons that can be accommodated in a shell with principal quantum number = Sum of the electrons in the constituent n subshells = 2n 2 . The shells are denoted by K, L, M, N, O---

8. Pauli’s Exclusion Principle Thank You