Atomic number: The number of protons in the nucleus of an atom of the element ... you remember the first 20 elements of the periodic table: H - Hydrogen He - Helium Li - Lithium Be - Beryllium ...

The modern periodic table is based closely on the ideas ... For example, one oxygen atom combines with two hydrogen atoms to make water (H₂O). A Russian scientist called Dmitri Mendeleev ...

The atom with eight protons in its nucleus (atomic number 8) is oxygen. Each energy level holds a certain number of electrons before electrons go into the next level. 1st Period: Hydrogen and ...

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.

The modern periodic table is based closely on the ideas ... For example, one oxygen atom combines with two hydrogen atoms to make water (H₂O). A Russian scientist called Dmitri Mendeleev ...