3d. The covalent bonding in the hydrogen molecule

Doc Brown's Chemistry: Chemical Bonding and structure GCSE level, IGCSE, O, IB, AS, A level US grade 9-12 level Revision Notes


Covalent bonding diagram for HYDROGEN covalent molecule, molecular formula H2

* metals \ non-metals (zig-zag line)

Pd metals Part of the modern Periodic Table

Pd = period, Gp = group

metals => non–metals
Gp1 Gp2 Gp3 Gp4 Gp5 Gp6 Gp7 Gp0
1 1H  Note that hydrogen does not readily fit into any group but is a non-metal 2He
2 3Li 4Be atomic number Chemical Symbol eg 4Be 5B 6C 7N 8O 9F 10Ne
3 11Na 12Mg 13Al 14Si 15P 16S 17Cl 18Ar
4 19K 20Ca 21Sc 22Ti 23V 24Cr 25Mn 26Fe 27Co 28Ni 29Cu 30Zn 31Ga 32Ge 33As 34Se 35Br 36Kr
5 37Rb 38Sr 39Y 40Zr 41Nb 42Mo 43Tc 44Ru 45Rh 46Pd 47Ag 48Cd 49In 50Sn 51Sb 52Te 53I 54Xe
6 55Cs 56Ba Transition Metals 81Tl 82Pb 83Bi 84Po 85At 86Rn
The covalent molecule hydrogen from combining with itself

 

Two hydrogen atoms (1) form the molecule of the element hydrogen H2

Hydrogen, a H atom, is one short of a full shell like helium, so two hydrogen atoms share each others electron to have a full outer shell.

(c) doc b and (c) doc b combine to form (c) doc b where both atoms have a pseudo helium structure of 2 outer electrons around each atom's nucleus. Any covalent bond is formed from the mutual attraction of two positive hydrogen nuclei and negative electrons between them (i.e. effectively 'electron sharing'), in this case a single H-H bond.

Incidentally, the nuclei would be a very tiny dot in the middle of where the H symbols are drawn! H valency is 1.

The Lewis diagram of hydrogen is the most simplified 'dot and cross' style of electronic diagram for the covalently bonded hydrogen molecule.

dot and cross diagram of the hydrogen molecule The hydrogen molecule is held together by the strong hydrogen–hydrogen single covalent bond H–H (displayed formula, a simple representation of the single bond but no electronic structure detail).

Remember, electronically, hydrogen is simply 1 and becomes like helium 2, so the hydrogen atoms effectively have a full outer shell in forming the covalent bonds when the atoms share their outer electrons. This last diagram of the hydrogen molecule shows the sharing of electrons bond in an overlap 'Venn diagram' style.

The - line in H-H represents the single covalent bond, in this simplest possible displayed formula


Comments

Hydrogen is a colourless gas at room temperature.

Melting point of hydrogen -259 oC

Boiling point of hydrogen -253 oC

Helium is the only element with a lower melting point and boiling point than hydrogen.

If hydrogen is mixed with air, the strong H-H bond stops it reacting with oxygen - too high an activation energy.

However, a flame provides enough energy to initiate the reaction - hence the 'squeaky pop' test for hydrogen!


What next?

Recommend next: The covalent bonding in the chlorine molecule

Explaining the properties of small covalently bonded molecules

 

Sub-index for Part 3. Covalent Bonding: small molecules & properties

 

Index for ALL chemical bonding and structure notes

 

Perhaps of interest?

Hydrogen is formed by the reaction of acids with metals

Gas preparations

 

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