1st Period: Hydrogen and helium—Electrons go into the first energy level. After the first level has two electrons, the next electron goes into the second level. 2nd Period: Lithium to neon—Electrons ...

As you move down a group in the periodic table, the covalent radius increases. Atoms increase in size. This is because of the screening effect of the filled inner electron levels. These electrons ...

The picture shows a close-up of one carbon atom. A hydrogen atom has one proton as the nucleus and one electron in the region outside the nucleus. The electron and proton are attracted to each other.