]> A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. The term is also used to refer to a pure chemical substance composed of atoms with the same number of protons. [Wikipedia] 13 14 18 22 33 42 5 6 4 5 45 35 2 6 6 2 3 5 6 7 8 10 12 2 20 20 65 48 28 24 18 17 2 4 34 29 9 10 2 3 4 30 26 2 3 0 1 2 3 4 1 6 8 10 16 2 2 80 121 53 74 20 19 3 4 12 12 25 30 42 54 7 7 2 11 12 10 10 8 8 2 -1 -1 3 A nearly colorless gas, it is a very strong absorber of ultraviolet radiation, and the presence of the ozone layer in the upper atmosphere provides an ozone shield that prevents dangerous radiation from reaching the earth's surface. -1 4 5 1 16 15 125 82 86 136 16 16 51 71 34 45 14 18 90 142 92 146 30 34