organizes all discovered chemical elements in rows (called periods) and columns (called groups) according to increasing atomic number. Scientists use the periodic table to quickly refer to information ...

The telluric screw plotted the atomic weights of the elements on the outside of a cylinder ... were not discovered until much later, which explains why there was a periodicity of 7 and not 8 in ...

Hence atomic number = 18 Number of protons + neutrons ... Similarly, the atoms of all group 7 elements have similar chemical properties and reactions to each other because all of them have ...