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In 1904, Richard Abegg formulated what is now known as Abegg’s rule, which states that the difference between the maximum positive and negative valence of an element is usually eight. In 1916, Gilbert N. Lewis used it to formulate the “octet rule” in his theory of cubic atoms: atoms will react to bring themselves into the most stable state. A full octet is very stable because all tracks will be full. Atoms with higher stability have less energy, so reactions that increase atomic stability will release energy in the form of heat or light.
Octet rule
This section will give you an introduction to the octet rule. The octet rule dictates that atoms gain or lose electrons to achieve the shell electron configuration closest to that of a noble gas. The attraction between atoms is measured informally by this rule. The octet rule specifies the electron’s position in the orbital of the atomic nucleus. It also determines whether electrons are added or lost through chemical reactions and measures the chemical reactivity of atoms based on their specific electron configuration.
Example 1: NaCl
The formula for table salt is NaCl. This is the result of the bonding of Na+ and Cl- ions. If sodium metal and chlorine gas are mixed under the right conditions, they form salts. Sodium loses an electron, and chlorine gains this electron. This releases a lot of light and heat. The resulting salt is usually non-reactive; it is stable. Unlike the sodium and chlorine that make it up, it doesn’t react explosively. Why?
Solution
Referring to the octet rule, an atom tries to achieve a noble gas electron configuration: eight valence electrons. Sodium possesses only one valence electron; giving it up would result in the same electron configuration as neon. Chlorine has seven valence electrons, so it has eight (one byte) if you add one. Chlorine has the electron configuration of argon when it gains electrons.
The octet rule will be satisfied if chlorine gives up its seven valence electrons and is taken up by sodium. In this case, both will have the electron configuration of a noble gas with a complete valence shell. However, Na7- and Cl7+ are much less stable than Na+ and Cl-. If atoms have little or no charge, they are more stable.
Limitation of the octet rule
Each element tends to gain eight electrons in its outer shell to achieve a noble gas configuration. But there are also limitations: (I) octet contraction and (II) octet expansion. There are many compounds in which atoms cannot complete their octets; an atom contains fewer or more than eight electrons in its outer valence shell.
Do most transition metals not follow the octet rule?
The octet rule is a guide for explaining simple bonding among common elements that typically appear in the first three rows of the periodic table (PT). The second and third rows of the PT are for elements that follow the octet rule because the shell contains only eight electrons. It should be noted that the first row of the PT also does not follow the octet rule since the layer is filled when it contains only two electrons. The fourth row shows the 3D orbital: 10 extra electrons can be accommodated, bringing the maximum electron count to 18. In row six, the 4f orbital comes into play, adding capacity for 14 extra electrons.
A KLMNOPQ shell can contain up to 2:8:8:18:18:32:32, which covers most PT elements. As we pass bismuth, these elements are either somewhat dangerous to use or extremely rare/man-made, and their chemistry may never be fully explored.
Needless to say, after PT row 4 (level 4), the story gets more complicated. Fortunately, the bonding conditions for most common elements that we need to understand in everyday scientific chemistry are relatively simple, so it is unnecessary to get into the bonding of heavy elements.
Conclusion
The octet rule describes how elements typically form bonds so that they can reach eight electrons in their valence shells to become noble gases. Noble gases have outer shells, and electrons occupy all available space. Applying this rule predicts the coupled behaviour and responsiveness of elements. Except for noble gases, all elements have insufficient or excessive electrons in their valence shells, resulting in a positive or negative charge. Atoms of elements tend to react to achieve the electronic configurations of noble gases.
While this rule generally applies to metals and metalloids, it is not very useful for dealing with transition element compounds where d or f orbitals are involved in bonding. Furthermore, this rule does not accurately predict the electronic configuration of all molecules and compounds. Therefore, this rule must be used carefully when predicting electron configurations. Atoms that follow the octet rule are more stable and emit less energy.
