Lewis Structures
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- 25288
The diatomic hydrogen molecule (H2) is the simplest model of a covalent bond, and is represented in Lewis structures as:
The shared pair of electrons provides each hydrogen atom with two electrons in its valence shell (the 1s) orbital.
Note
In a sense, it has the electron configuration of the noble gas helium
When two chlorine atoms covalently bond to form \(Cl_2\), the following sharing of electrons occurs:
Each chlorine atom shared the bonding pair of electrons and achieves the electron configuration of the noble gas argon. In Lewis structures the bonding pair of electrons is usually displayed as a line, and the unshared electrons as dots:
The shared electrons are not located in a fixed position between the nuclei. In the case of the \(H_2\) compound, the electron density is concentrated between the two nuclei:
The two atoms are bound into the \(H_2\) molecule mainly due to the attraction of the positively charged nuclei for the negatively charged electron cloud located between them
For the nonmetals (and the 's' block metals) the number of valence electrons is equal to the group number:
Element |
Group |
Valence electrons |
Bonds needed to form valence octet |
F |
7A |
7 |
1 |
O |
6A |
6 |
2 |
N |
5A |
5 |
3 |
C |
4A |
4 |
4 |
Examples of hydride compounds of the above elements (covalent bonds with hydrogen:
Thus, the Lewis bonds successfully describe the covalent interactions between various nonmetal elements
Multiple bonds
The sharing of a pair of electrons represents a single covalent bond, usually just referred to as a single bond . However, in many molecules atoms attain complete octets by sharing more than one pair of electrons between them.
- Two electron pairs shared a double bond
- Three electron pairs shared a triple bond
Because each nitrogen contains 5 valence electrons, they need to share 3 pairs to each achieve a valence octet.
- N2 is fairly inert, due to the strong triple bond between the two nitrogens
- The N - N bond distance in N2 is 1.10 Å (fairly short)
From a study of various Nitrogen containing compounds bond distance as a function of bond type can be summarized as follows:
- \(\ce{N-N}\): 1.47Å
- \(\ce{N=N}\): 1.24Å
- \(\ce{N:=N}\):1.10Å