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 table to explore the following observations ... In PCl5, phosphorous is surrounded by ten electrons. The compunds PF6- can also be ...

As you move from left to right across the periodic table, atoms have more electrons in their outer energy level and more protons in their nucleus. The greater attraction between the increased ...

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 ...

In contrast, P-type semiconductors use a dopant element from group III on the periodic table (such as boron, indium, or gallium). These elements have only three electrons in their valence shell ...