Elements in the same horizontal row are in the same period. The periods are numbered from top to bottom. The period number is the same as the number of occupied electron shells.

This page uses out understanding of the atomic model and the periodic ... 12 electrons around phosphorous! Look at electron configuration of nitrogen v. phosphorous (image of box/arrow diagrams of ...

It is not possible to locate the exact position of an electron, but the electron cloud shows the region where an electron is most likely to be. When the plastic strip is rubbed on the skin, electrons ...

We find that it is the 4s orbital electrons that are ionised first before the 3d orbitals. We have to conclude that, ironically for the d-block elements, the 4s orbitals are in fact higher in energy ...