How can i convert real number to round that number?

Answer 1

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 "K shell"), followed by the "2 shell" (or "L shell"), then the "3 shell" (or "M shell"), and so on further and further from the nucleus. The shell letters K, L, M, ... are alphabetical.

Each shell can contain only a fixed number of electrons: The 1 shell can hold up to two electrons, the 2 shell can hold up to eight electrons, and in general, the n shell can hold up to 2n2 electrons. Since electrons are electrically attracted to the nucleus, an atom's electrons will generally occupy outer shells only if the more inner shells have already been completely filled by other electrons. However, this is not a strict requirement: Atoms may have two or even three outer shells that are only partly filled with electrons. (See Madelung rule for more details.) For an explanation of why electrons exist in these shells see electron configuration.[1]