The most common type of exception to the octet rule are compounds or ions with central atoms having more than eight electrons around them. PF_. \(\mathrm{PF}_{5}, \mathrm{SF}_{4}, \mathrm{ClF}_{3}\) and \(\mathrm{Br}_{3}^{-}\) are examples of this type of exception. Draw the Lewis structure for these compounds or ions. Which elements, when they have to, can have more than eight electrons around them? How is this rationalized?

Short Answer

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The Lewis structures for the given compounds or ions are: PF5: F - P - F | | F - P - F SF4: F - S - F | | F F ClF3: F - Cl - F | F Br3-: Br - Br - Br | | 2e 2e Elements in period 3 or below, like P, S, and Cl, can have more than eight electrons around them due to their empty d-orbitals, which allow for an expanded octet or hypervalency.

Step by step solution

01

Count Valence Electrons

For each compound or ion, calculate the total number of valence electrons. PF5: P: 5 valence electrons (group 15) F: 7 valence electrons each (group 17) Total valence electrons = 5 + (5 × 7) = 40 SF4: S: 6 valence electrons (group 16) F: 7 valence electrons each (group 17) Total valence electrons = 6 + (4 × 7) = 34 ClF3: Cl: 7 valence electrons (group 17) F: 7 valence electrons each (group 17) Total valence electrons = 7 + (3 × 7) = 28 Br3-: Br: 7 valence electrons each (group 17) Extra electron due to negative charge: 1 electron Total valence electrons = 3 × 7 + 1 = 22
02

Draw Skeleton Structures

Now, draw the skeleton structure for each compound or ion with the central atom bonded to the surrounding atoms. PF5: F | P - F | F SF4: F | S - F | F ClF3: F | Cl | F - F Br3-: Br - Br - Br
03

Place Remaining Electrons

Next, place the remaining valence electrons around each central atom to fill their octets and complete the Lewis structures: PF5: F - P - F | | F - P - F SF4: F - S - F | | F F ClF3: F - Cl - F | F Br3-: Br - Br - Br | | 2e 2e
04

Determine Elements with More Than Eight Electrons and Rationalize

In the Lewis structures for PF5, SF4, and ClF3, the central atoms have more than eight electrons around them: P has 10 electrons, S has 10 electrons, and Cl has 10 electrons. These elements can accommodate more than eight electrons because they are in period 3 or below and have empty d-orbitals to accommodate additional electrons. This phenomenon is known as the "expanded octet" or "hypervalency." In conclusion, elements in period 3 or below, like P, S, and Cl, can have more than eight electrons around them due to their empty d-orbitals, which allow for an expanded octet or hypervalency. The Lewis structures for the given compounds or ions are as follows: PF5: F - P - F | | F - P - F SF4: F - S - F | | F F ClF3: F - Cl - F | F Br3-: Br - Br - Br | | 2e 2e

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