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.

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 ...

The “lead” of a pencil is actually made of a substance called graphite which is made of carbon atoms. The picture shows a close-up of one carbon atom. A hydrogen atom has one proton as the nucleus and ...

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 ...