<human>:  Why is there a gap between the elements helium and lithium on the Periodic Table of Atoms?
<bot>: The gap between helium and lithium is because there are no stable elements between them. Helium is the second lightest element, and lithium is the third lightest element. Helium is a noble gas, which means that it is not reactive. Lithium is a reactive metal, which means that it reacts with other elements.