In inorganic chemistry, elements are organized and studied by groups in the periodic table. Let us begin with the simplest element, hydrogen, and the chemically very stable noble gases.
Basic Knowledge
Hydrogen H has atomic number 1 and electron configuration 1s1. It is a unique element that shows properties of both alkali metals (monovalent cations) and halogens (monovalent anions). Industrially, it is mass-produced by steam reforming CH4 + H2O → CO + 3H2 and is used as a raw material for ammonia synthesis and fuel cells.
Noble gases (Group 18) are He, Ne, Ar, Kr, Xe, and Rn. Because their outer electron shells are closed, they are chemically inert and exist as monatomic molecules. Their abundance in air is in the order Ar (0.93%) > Ne > He > Kr > Xe. He is used in hot-air balloons and MRI cooling, Ar as a shielding gas for welding, Kr in lasers, and Xe in anesthesia and automobile headlamps.
Hydrogen (colorless and odorless, the lightest gas, produces water when burned)
Steam reforming (CH4+H2O→CO+3H2, an industrial hydrogen-production method)
Noble gases (inert gases in Group 18, existing as monatomic molecules)
Closed-shell structure (stable structure with a filled outer electron shell)
Avogadro constant (6.02×1023/mol, used to convert the volume of 1 mol of noble gas)
XeF2, XeF4 (examples of compounds of heavy noble gases)
Further Study (Principles and Applications)
Hydrogen is a candidate for future clean energy. Green hydrogen is produced by electrolyzing water with renewable electricity, while blue hydrogen is produced from fossil fuels with CO2 capture. In fuel-cell vehicles (FCVs), electricity is obtained through 2H2 + O2 → 2H2O.
The inertness of noble gases was challenged in 1962 when Bartlett synthesized XePtF6. Today, fluorides such as XeF2 and KrF2 are known. He easily escapes from Earth's atmosphere, and separation from underground natural-gas fields is its only economically viable source. It is therefore important as a strategic resource.
- Hydrogen is a special element whose position in the periodic table is debated
- Steam reforming is the main industrial method of producing hydrogen
- Noble gases are inert and monatomic because of their closed-shell structures
- Ar is the most abundant noble gas in air (0.93%)
- Xe and Kr form compounds as fluorides
- There is no economically viable source of He other than separation from natural-gas fields
- They have many industrial applications, including neon tubes, fluorescent lamps, MRI, and welding
Points to Note (Common Confusions and Frequent Mistakes)
① Hydrogen is placed in Group 1 but is not an alkali metal. ② Noble gases are also called “inert gases” (the current IUPAC terminology is “noble gases”). ③ He has a closed shell with 1s2, even though it has only two electrons. ④ The bond in the hydrogen molecule H2 is a covalent bond (σ bond).
Practice
- Write the reaction equation for steam reforming.
- What is the most abundant noble gas in the atmosphere? Answer with its volume percentage.
- State the overall reaction equation of a fuel cell and the environmental significance of releasing only water.