To determine the number of electrons present in the M shell of an atom with an atomic number of 20, we need to understand the arrangement of electrons in different shells according to the rules of electron configuration.
1. Identify the total number of electrons: For an atom with atomic number 20, there are 20 electrons.
2. Electron distribution in shells: Electrons are arranged in shells around the nucleus following the 2n² rule, where n is the shell number (principal quantum number).
- K shell (n=1): [tex]\(2 \times (1)^2 = 2 \)[/tex] electrons
- L shell (n=2): [tex]\(2 \times (2)^2 = 8 \)[/tex] electrons
- M shell (n=3): [tex]\(2 \times (3)^2 = 18 \)[/tex] electrons (but only up to 8 electrons can be filled in practice for elements in the first few periods to follow the octet rule for stability)
- N shell (n=4): Remaining electrons after filling K, L, and M shells
3. Filling the shells:
- K shell: The first 2 electrons are placed in the K shell.
- L shell: The next 8 electrons fill the L shell.
- M shell: After filling K and L shells, we have [tex]\(20 - 2 - 8 = 10\)[/tex] electrons left. According to the practical electron distribution and the octet rule, up to 8 electrons can be placed in the M shell.
- N shell: The remaining 2 electrons will be placed in the N shell.
Thus, the number of electrons in the M shell of an atom with an atomic number of 20 is 8.
Correct Answer: (C) 8
