It's understandable that the terminology used in atomic physics can be confusing. However, it's important to clarify a few concepts related to atomic weight or atomic mass.
Firstly, atomic weight or atomic mass is not the same as the weight of an atom in the gravitational sense. Atomic weight refers to the average mass of the atoms of a particular element, taking into account the relative abundances of its isotopes. It is based on the atomic mass unit (u) scale, where 1 atomic mass unit is defined as 1/12th the mass of a carbon-12 atom.
Hydrogen and helium are indeed light elements, and they have relatively low atomic masses compared to heavier elements. The atomic weight of hydrogen is approximately 1.008 u, and the atomic weight of helium is approximately 4.0026 u. These values represent the average masses of naturally occurring isotopes of these elements.
Additionally, atomic weights are not negative numbers. The atomic weight scale is a relative scale, and it does not have negative values. Negative values are not used to represent atomic weights, as they would not provide meaningful information about the mass of an element's atoms.
In summary, the atomic weights of hydrogen and helium are positive values that represent the average masses of the isotopes of these elements. They are not directly related to the gravitational weight or behavior of atoms.