Octet rule (including exceptions) In covalent molecules the atoms “want to” reach a stable 8-electron noble gas The central atom has formally
“octet rule” by sharing two electrons only Two hydrogen atoms form a covalent bond to make a hydrogen molecule Each contributes one electron
Carbon, nitrogen, oxygen, and fluorine must always follow the octet rule How to draw Lewis dot structures: 1) Determine the central atom
If no electrons are left and the central atom is not yet surrounded by four electron pairs (octet rule), convert one or more lone pairs from a terminal atom to
number of electrons in the valence shell of the central atom in a hypervalent molecule is less than 8; in other words, the modified octet rule is obeyed
Exceptions to the Octet Rule ? In those cases where the octet rule does not apply, the substituents attached to the central atom nearly
For example, sulfur, the central atom in SF6, has 12 electrons around it, exceeding the octet rule See pg 601 of your text ASSIGNING FORMAL CHARGE ON ATOMS
Lewis dot structures show valence electrons surrounding atom We visualize the four OCTET RULE – Generally atoms prefer electron configurations with 8 valence electrons Atoms bond note hydrogen is first exception to octet rule Fluorine on peripheral atoms to bonds between central atom and peripheral atom 8
OCTET RULE The atoms that participate in covalent bonding share electrons in a way that enables them to acquire a stable shares 2 Thus every atom in this stable molecule fulfills the octet rule C “EXCEPTIONS” TO THE OCTET RULE
I All smaller atoms want eight valence electrons (Octet Rule) A Except for Place any extra electrons on the central atom of these even if it already has eight VII Acidic and D This explains the octet rule exceptions (Ex BeF2) VSEPR
given the formula, ABn, A is the central atom in the structure (but not always), and B atoms flank There are generally three type of exception to the Octet Rule
The most important rule for predicting the way atoms achieve octets on all atoms (see exceptions) Put other atoms around central atom and connect with a