Chemical Reactivity - Hydrogen Unlike the rest of the Group...

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Hydrogen Unlike the rest of the Group 1A elements, which exist as metals, elemental hydrogen exists as gaseous  H 2  molecules. Compounds formed between hydrogen and non-metals are molecular rather than ionic. ( i.e. hydrogen forms covalent bonds with non-metals). For example, hydrogen reacts with halogens (Group VIIA)  according to: H 2 (g)  + X 2    2 HX (g) where  X  can be any halogen, such as  F Cl Br , or  I . Hydrogen in these compounds has an oxidation state of  +1 while the halogens are -1. Similarly, hydrogen reacts to other elemental non-metals in a predictable fashion: 2 H 2 (g)  + O 2(g)    2 H 2 O (g) 8 H 2 (g)  + S 8(s)    8 H 2 S (g) 3 H 2 (g)  + N 2(g)    2 NH 3(g) Hydrogen can also form compunds with more active metals to form  ionic hydrides . For example, lithium  hydride is formed according to: 2 Li (s)  + H 2 (g)    2 LiH (s) The metal ( Li  in this case) loses an electron to become a cation and  H  gains an electron to become  H -  (hydride  anion), which has an charge of -1. Here's another example: Mg (s)  + H 2 (g)    MgH 2(s) By gaining an electron, the hydride ion obtains the stable electron configuration of a closed 
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This note was uploaded on 10/13/2011 for the course CHEMISTRY 121 taught by Professor Staff during the Fall '10 term at Bangladesh University of Eng and Tech.

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Chemical Reactivity - Hydrogen Unlike the rest of the Group...

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