Properties of Hydrogen 

Hydrogen is a nonmetal and is placed above group in the periodic table because it has ns¹ electron configuration like the alkali metals. However, it varies greatly from the alkali metals as it forms cations (H⁺) more reluctantly than the other alkali metals.  Hydrogen‘s ionization energy is 1312 kJ/mol, while lithium (the alkali metal with the highest ionization energy) has an ionization energy of 520 kJ/mol.

Because hydrogen is a nonmetal and forms H^- (hydride anions), it is sometimes placed above the halogens in the periodic table.  Hydrogen also forms H₂ dihydrogen like halogens.  However, hydrogen is very different from the halogens.  Hydrogen has a much smaller electron affinity than the halogens.    

H₂ dihydrogen or molecular hydrogen is non-polar with two electrons.  There are weak attractive forces between H₂ molecules, resulting in low boiling and melting points.  However, H₂ has very strong intramolecular forces; H₂ reactions are generally slow at room temperature due to strong H—H bond.  H₂ is easily activated by heat, irradiation, or catalysis.  Activated hydrogen gas reacts very quickly and exothermically with many substances. 

Hydrogen also has an ability to form covalent bonds with a large variety of substances. Because it makes strong O—H bonds, it is a good reducing agent for metal oxides.  Example: CuO(s) + H₂(g) → Cu(s) + H₂O(g) H₂(g) passes over CuO(s) to reduce the Cu²⁺ to Cu(s), while getting oxidized itself.

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