The document discusses the octet rule and its limitations, initially influenced by Richard Abegg's rule which noted a commonality in valence electron configurations. It highlights the breakthroughs by Kossel and Lewis in 1916 that shaped modern chemistry, detailing the octet rule's role in chemical bonding and stability. However, it also points out significant limitations such as incomplete and expanded octets, and the eventual challenges posed by quantum mechanics to traditional theories of bonding.

1. Submitted by:
Sharan Keshav (Roll no: 30)
Rajiv Sukesh (Roll no: 20)
Anirudh A G (Roll no: 2)
Ilamparithi (Roll no: 7)
(Students of XI A8)
The Octet Rule and its Limitations

2. ABEGG'S RULE
• Before octet rule was theorized, there were always methods to approach electron
configuration. The most famous was Richard Abegg's attempt in 1904 known as the
Abegg's rule.
• It stated that the difference between the maximum positive and negative valences of
an element is frequently eight.
• Abegg's rule was the cornerstone for various chemical achievements of his time and
also enabled us to proceed forward with the octet rule.
• The rule also had its own exceptions and limitations (such as the odd and even
fallacy and hydrogen's exception).
(Richard Abegg)
This is a Sulphur Atom. It has 6 Valence
electrons.It can gain a maximum of 2
electrons (H2S) and lose a maximum of
6 electrons (H2SO4). Sum of their
absolute values 6 + 2 = 8

3. OCTET RULE
• Abegg's rule as discussed before opened a new wave of research into the valence
electrons of an atom. In 1916,Kössel and Lewis made a breakthrough with help of the
octet rule.
• It stated that, atoms can combine either by transfer of valence electrons from one
atom to another (gaining or losing) or by sharing of valence electrons in order to
have an octet in their valence shells.“Octet”means a group of 8
• It was a remarkable breakthrough in science which helped redefine our ways of
thinking about chemistry as a whole.
Walther Kossel G.N.Lewis

4. ACHIEVEMENTS
While it is clear about how important the octet rule was, here are some of its commonly
known achievements:
• The octet rule successfully explains the formation of chemical bonds depending
upon the nature of the element.
• It is used to determine stability in atoms.
• The octet rule helps to figure out how atoms will bond with one another

5. LIMITATIONS(LANGMUIR)
• Irving Langmuir was a 38-year-old research chemist at General Electric when he
first began to write on the subject of Lewis’ electron pair bonding
• He went on to extend the theory -- Langmuir’s postulated shells sequence of 2, 8,8,18,
18,and 32 and the introduction of a static molecule
• Unfortunately his ambitions were short-lived as many physicists such as Bohr began to
identify flaws in his papers and this lead to the hole in the octet rule
• It also sparked a huge debate between Lewis and Langmuir about electron
deficient hydrides
Irving Langumir
Langmuir’s cubical atom models
Covalent Bonding (A->B->C)

6. LIMITATIONS
The octet rule had many flaws.The most significant being:
• The Incomplete octet: In certain molecules such as BeH2, BeCl2, BH3,BF3, the central atom has less
than 8 electrons in its valence shell, yet the molecule is stable.
• The Expanded octet: In certain molecules such as PF5, SF6, IF7, H2SO4,the central atom has more than
8 valence electrons,yet the molecule is stable.

7. • The octet rule also failed to predict the shape and the relative stability of the molecules.
• Furthermore the recent quantum mechanical calculations have tended to discount the importance of
octet expansion and have reinstated the general validity of the octet rule for the p-block elements.
• Also, modern bonding theory has also provided a satisfactory resolution of the problems associated
with both electron-deficient and electron-rich species and has done so in such a way that neither
Langmuir nor Lewis was correct.
LIMITATIONS

8. In conclusion, when all is said and done, this story and breakthrough was for the
history books (and in this case chemistry books as well). While the theory is not
as useful and relevant as it initially was, it lead to a large scientific diversion
about thinking on the bonding of atoms and valence electrons as a whole.
Thank You!