Share ; Comment(0) Add Comment. • In such cases the octet rule is broken, not obeyed. Hyper valence: • The octet rule is obeyed by elements in period 2 (Li → Ne) strictly. Byjus Asked on June 11, 2016 in Chemistry. Check all that apply. Another friend of yours says that this is because the heavier elements are larger and can make bonds to more than four atoms at a time. One exception to the octet rule is that in the real world some atoms in molecules or compounds do have fewer than eight (octet) valence electrons. For elements in the third row of the periodic table and beyond, the octet rule is often not obeyed. 5)[SnF6]2− Exceptions to the octet rule include the following: Some atoms have fewer than eight valence electrons. In a molecule of phosphorus pentachloride, #PCl_5#, each chlorine atom ends up with an octet of electrons (four pairs), but the phosphorus atom ends up with ten electrons (five pairs). 2) Incomplete octets : group IIA and IIIA elements. Molecules that combine to have an odd number of valence electrons don't follow the octet rule. A valence shell is the outer shell of an atom. 1)PH3. The other halogen molecules (F 2, Br 2, I 2, and At 2) form bonds like those in the chlorine molecule: one single bond between atoms and three lone pairs of electrons per atom.This allows each halogen atom to have a noble gas electron configuration, which corresponds to eight valence electrons. Draw the Lewis structures for each of the following molecules or ions. The chlorine atoms obey the octet rule, but the phosphorus atom does not. Species with incomplete octets are pretty rare and generally are only found in some beryllium, aluminum, and boron compounds including the boron hydrides. Include all formal charges and lone-pair electrons. 3)N3− 4)CH2Cl2. There are an insufficient number of total electrons available for all the atoms in the borate ion to have an octet Draw a single Lewis structure for the phosphate ion (PO43−), in which the octet rule is obeyed. This is also the case with incomplete octets. 4. Among the following molecules octet rule is not obeyed by: 0; Chemistry ; The central atom of ClF 3 has more than eight electrons in its valence shell and forms super octet molecule. But elements in periods 3→6 do form compounds in which the central atom has more than eight electrons around it, most common being 10 or 12. There are three categories of molecules that don't follow the octet rule: 1) Lewis Structures that have an odd number of valance electrons. Identify the ions and molecules in which the octet rule is not obeyed. The octet rule is one of the chemical “rules of thumb” stating that atoms prefer to combine in a manner such that each atom has 8 electrons in their valence shells. 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