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Heavy Elements usually elements which have atomic weights greater than iron

Light elements
The chemical elements produced during the first minutes of existence of the Universe. They are helium, deuterium (an isotope of hydrogen), lithium, beryllium and boron. They are called 'light elements' because their nuclei are made of just a few nuclear particles, and thus their mass is very low. The other elements - those produced in the core of stars - are 'heavier'; iron, for instance, has 26 protons in its nucleus. See also Nucleosynthesis and Primordial nucleosynthesis.