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The N shell can hold a maximum of ____ electrons, but in Calcium (atomic number 20), it contains _____ electrons.
32, 2
18, 0
8, 2
32, 0
32, 0
The N shell (n=4) can hold a maximum of 2n2 electrons, which equals 2(4)2=32 electrons. However, in a Calcium atom (atomic number 20), the electronic configuration is 1s22s22p63s23p64s2, meaning the N shell (4th shell) contains only 2 electrons in the 4s subshell, while the M shell (3rd shell) is partially filled.
The N shell (n=4) can hold a maximum of 2n2 electrons, which equals 2(4)2=32 electrons. However, in a Calcium atom (atomic number 20), the electronic configuration is 1s22s22p63s23p64s2, meaning the N shell (4th shell) contains only 2 electrons in the 4s subshell, while the M shell (3rd shell) is partially filled.
Think of a hotel with multiple floors; the N shell is the 4th floor which has the capacity for 32 guests, but for a group of 20 guests (Calcium), only the first two rooms on the 4th floor are occupied, while the rest remain empty.
2n2 тАФ representing the maximum electron capacity of a shell where n is the shell number
The distribution of electrons follows the Bohr-Bury scheme and the Aufbau principle. Electrons fill lower energy orbitals before higher energy ones; in Calcium, the 3p subshell is filled, and the next two electrons enter the 4s subshell of the N shell, leaving the N shell's higher energy subshells (4p, 4d, 4f) empty.
Maximum capacity of shell n is calculated by 2n2.
Shells: K(n=1), L(n=2), M(n=3), N(n=4).
Calcium configuration: 2,8,8,2.
The 4th shell (N shell) in Calcium only has electrons in the 4s orbital.
Predicting chemical reactivity
Understanding valence shell electron configurations
Calcium (Ca) has 20 electrons: 1s2,2s2,2p6,3s2,3p6,4s2.
Option C is common confusion because students mistakenly apply the octet rule to all shells regardless of subshell energy levels.
D is correct тАФ The N shell has a theoretical capacity of 32 electrons (2├Ч42), but the Calcium atom's electronic configuration 2,8,8,2 places only 2 electrons in the N shell.
Always remember that the 2n2 rule gives the maximum capacity of the shell, but the actual number of electrons in a specific shell depends on the energy order determined by the Aufbau principle.