Question

How do you determine the number of electrons needed to fill the outer shell of an element?

Answer 1

In chemistry and atomic physics, an electron shell may be thought of as an orbit followed by electrons around an atom's nucleus. The closest shell to the nucleus is called the "1 shell" (also called the "K shell"), followed by the "2 shell" (or "L shell"), then the "3 shell" (or "M shell"), and so on further and farther from the nucleus. The shells correspond to the principal quantum numbers (n = 1, 2, 3, 4 ...) or are labeled alphabetically with the letters used in X-ray notation (K, L, M, …).

Complete step by step answer:

Only a certain amount of electrons can fit into each shell: The first shell may store two electrons, the second shell eight (2 + 6) electrons, the third shell 18 (2 + 6 + 10) electrons, and so forth. The nth shell may theoretically store up to $2{n}^2$ electrons, according to the general formula. See electron configuration for an explanation of why electrons exist in these shells. Each subshell is made up of one or more atomic orbitals, and each subshell is made up of one or more subshells.

As a result, the K shell, which includes just a s subshell, can hold up to 2 electrons; the L shell, which contains both a s and a p, can hold up to 2 + 6 = 8 electrons, and so on; the nth shell can store up to $2n^2$ electrons in general.

Note: Despite the fact that the formula yields the maximum in theory, the maximum is only attained (by known elements) for the first four shells (K, L, M, N). There are no known elements with more than 32 electrons in each shell. Because the subshells are filled according to the Aufbau principle, this is the case. The g-block of period 8 of the periodic table would include the first elements with more than 32 electrons in a single shell. These elements would contain some electrons in their 5g subshell, resulting in an O shell with more than 32 electrons (fifth principal shell).