What is the lightest known element?

Hydrogen is the lightest known element, and this is due to its atomic structure. It consists of one proton and usually one electron, making it the simplest and least massive of all elements. The atomic mass of hydrogen is approximately 1.008 atomic mass units (amu), which is significantly lower than that of any other element.

The atomic structure of hydrogen contributes to its status as the lightest element. Since atomic mass is a crucial factor in determining the weight of an element, and with hydrogen having the fewest particles, it occupies a unique position on the periodic table as element number one. This characteristic has important implications in various scientific fields, including chemistry and physics, where hydrogen plays a fundamental role in reactions and compounds.

While helium, oxygen, and lithium possess greater atomic masses compared to hydrogen, they all contain additional protons and neutrons, making them heavier. Helium, for instance, has two protons and two neutrons, giving it an atomic mass of about 4.0026 amu, while oxygen has eight protons and eight neutrons. Consequently, the comparative weight of hydrogen confirms its designation as the lightest element recognized today.