The Periodic Table is a well-organized chart that contains all 118 known elements in the universe. These elements are the ...

Argon is an inert gas in group VIII A of the periodic table with atomic number 18, an atomic weight of 39.948, and a density of 1.40 Mg/m 3. In the solid state it forms an fcc crystal with a melting ...

For example, the mass number of argon atoms and calcium atoms can both be 40. The symbol for an atom can be written to show its mass number at the top, and its atomic number at the bottom.