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Suppose there are 8 periods in the periodic table and each atomic orbital can hold a maximum of 5 electrons (instead of 2). How many elements would be present in period 8?

1. 50
2. 75
3. 100
4. 125

Correct answer: 125

Solution

With 5 electrons per orbital, each subshell with azimuthal quantum number l contains 5*(2l+1) electrons. Period 8 fills: 8s (1 orbital * 5 = 5 electrons), 5g (9 orbitals * 5 = 45 electrons), 6f (7 orbitals * 5 = 35 electrons), 7d (5 orbitals * 5 = 25 electrons), 8p (3 orbitals * 5 = 15 electrons). Total elements in period 8 = 5 + 45 + 35 + 25 + 15 = 125.

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