The lightest element on the periodic table is hydrogen. The atomic weight of hydrogen is 1.00794 and the atomic number is 1. Hydrogen is the most abundant element on the periodic table with 75 percent of the mass of the universe consisting of hydrogen.
The first element on the periodic table is hydrogen. The physical form of this element at room temperature is a colorless and odorless gas. Hydrogen has multiple uses, however, hydrogen is commonly used for producing ammonia and processing fossil fuels. Hydrogen is important in the study of superconductivity and its liquid form is used in cryogenics. Other common applications of hydrogen include filling balloons, producing hydrochloric acid, producing rocket fuel and creating fuel cells.