Class 11-science Answered
Expert Answer
Electrons move in regions of space surrounding the nucleus called orbitals. These orbitals can be regarded as being arranged in shells around the nucleus. These shells are major energy levels surrounding the nucleus. Shells are further divided into energy levels of similar energy called subshells. These subshells are given the labels of "s", "p", "d", "f" and "g".Subshells are further composed of orbitals, which, as discussed above, are regions of space around the nucleus in which electrons can be found. The subshells within a shell increase in energy in the following order, s<p<d<f<g. Orbitals can have 0, 1 or 2 electrons in them. This is known as thePauli exclusion principle.
A many electron atom fills its lowest energy shells first before proceeding to higher energy shells. The order of filling is
1s, 2s, 2p, 3s, 3p, 4s, 3d .
