Airships are filled with a lifting gas that is less dense than the surrounding air. The most commonly used lifting gases are hydrogen and helium. Hydrogen is an extremely flammable, diatomic gas whereas helium is a non-flammable,  monatomic gas. The danger of using extremely flammable hydrogen as a lifting gas was evidenced by the Hindenburg Disaster in 1937.  Being non-flammable, helium is much safer lifting gas than hydrogen. Helium is an inert element; does not react with other elements to form compounds. On the other hand, hydrogen is a reactive element; reacts with other elements to form compounds. What makes the properties of hydrogen different from those of helium? How are the properties of elements related to the structure of  the atoms? This chapter will describe the structure of atoms and the symbolism of atoms. Later on we will see how the properties of each element is related to the structure of the atoms.

                                         Figure 1. The Hindenburg bursts into flames above Lakehurst, New Jersey, on May 6, 1937