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The helium dimer can be formed in small amounts when helium gas expands and cools as it passes through a nozzle in a gas beam. [2] Only the isotope 4 He can form molecules like this; 4 He 3 He and 3 He 3 He do not exist, as they do not have a stable bound state. [6]
Molecular orbital diagrams are diagrams of molecular orbital (MO) energy levels, shown as short horizontal lines in the center, flanked by constituent atomic orbital (AO) energy levels for comparison, with the energy levels increasing from the bottom to the top. Lines, often dashed diagonal lines, connect MO levels with their constituent AO levels.
Complete acetylene (H–C≡C–H) molecular orbital set. The left column shows MO's which are occupied in the ground state, with the lowest-energy orbital at the top. The white and grey line visible in some MO's is the molecular axis passing through the nuclei.
Hydrogen, being the lightest existing gas (7% the density of air, 0.08988 g/L at STP), seems to be the most appropriate gas for lifting.It can be easily produced in large quantities, for example with the water-gas shift reaction or electrolysis, but hydrogen has several disadvantages:
The term bond-dissociation energy is similar to the related notion of bond-dissociation enthalpy (or bond enthalpy), which is sometimes used interchangeably.However, some authors make the distinction that the bond-dissociation energy (D 0) refers to the enthalpy change at 0 K, while the term bond-dissociation enthalpy is used for the enthalpy change at 298 K (unambiguously denoted DH° 298).
A hydrogen-like atom (or hydrogenic atom) is any atom or ion with a single valence electron.These atoms are isoelectronic with hydrogen.Examples of hydrogen-like atoms include, but are not limited to, hydrogen itself, all alkali metals such as Rb and Cs, singly ionized alkaline earth metals such as Ca + and Sr + and other ions such as He +, Li 2+, and Be 3+ and isotopes of any of the above.
In chemistry, homonuclear molecules, or elemental molecules, or homonuclear species, are molecules composed of only one element.Homonuclear molecules may consist of various numbers of atoms.
For hydrocarbons, the DBE (or IHD) tells us the number of rings and/or extra bonds in a non-saturated structure, which equals the number of hydrogen pairs that are required to make the structure saturated, simply because joining two elements to form a ring or adding one extra bond (e.g., a single bond changed to a double bond) in a structure reduces the need for two H's.