<P> In 1923, the American scientist Robert H. Goddard became the first person to develop a rocket engine that burned liquid fuel; the engine used gasoline for fuel and liquid oxygen as the oxidizer . Goddard successfully flew a small liquid - fueled rocket 56 m at 97 km / h on March 16, 1926 in Auburn, Massachusetts, US . </P> <P> Oxygen levels in the atmosphere are trending slightly downward globally, possibly because of fossil - fuel burning . </P> <P> At standard temperature and pressure, oxygen is a colorless, odorless, and tasteless gas with the molecular formula O 2, referred to as dioxygen . </P> <P> As dioxygen, two oxygen atoms are chemically bound to each other . The bond can be variously described based on level of theory, but is reasonably and simply described as a covalent double bond that results from the filling of molecular orbitals formed from the atomic orbitals of the individual oxygen atoms, the filling of which results in a bond order of two . More specifically, the double bond is the result of sequential, low - to - high energy, or Aufbau, filling of orbitals, and the resulting cancellation of contributions from the 2s electrons, after sequential filling of the low σ and σ orbitals; σ overlap of the two atomic 2p orbitals that lie along the O-O molecular axis and π overlap of two pairs of atomic 2p orbitals perpendicular to the O-O molecular axis, and then cancellation of contributions from the remaining two of the six 2p electrons after their partial filling of the lowest π and π orbitals . </P>

Is a process that derives energy from organic molecules in the presence of oxygen