The diameter of a hydrogen atom is about $\displaystyle{5}\times{{10}}^{{-{{11}}}}\usepackage{cmbright}\Huge\$ meters. Suppose $\displaystyle{8.4}\times{{10}}^{{5}}\usepackage{cmbright}\Huge\$ hydrogen atoms were arranged side by side in a straight line. Multiply these numbers to find the length of this line of atoms. What is the length in scientific notation?