To determine which of the given compounds demonstrates an exception to the octet rule, we first need to understand what the octet rule is. The octet rule states that atoms tend to form compounds in ways that give them eight valence electrons, leading to a more stable arrangement similar to that of noble gases.
Let's examine each of the compounds to see if they adhere to or deviate from the octet rule:
1. SF₆ (Sulfur Hexafluoride):
- Sulfur (S) has 6 valence electrons.
- Each of the 6 Fluorine (F) atoms has 7 valence electrons.
- When sulfur forms bonds with six fluorine atoms, it shares its electrons with each fluorine. This results in sulfur having 12 electrons around it (6 from sulfur itself and 6 shared from fluorine atoms), which exceeds the octet rule.
- Therefore, SF₆ has 12 electrons around sulfur, making it an exception to the octet rule.
2. H₂O (Water):
- Oxygen (O) has 6 valence electrons.
- Each Hydrogen (H) atom has 1 valence electron.
- When oxygen bonds with two hydrogen atoms, it shares electrons to complete its octet (8 electrons in total).
- Therefore, H₂O follows the octet rule.
3. C₂H₆ (Ethane):
- Each Carbon (C) atom has 4 valence electrons.
- Each Hydrogen (H) atom has 1 valence electron.
- In C₂H₆, each carbon atom forms three bonds with hydrogen atoms and shares another pair of electrons in a single bond with the other carbon atom, resulting in each carbon having 8 electrons.
- Therefore, C₂H₆ follows the octet rule.
4. KCl (Potassium Chloride):
- Potassium (K) has 1 valence electron, and Chlorine (Cl) has 7 valence electrons.
- Potassium donates its 1 valence electron to chlorine, resulting in K⁺ and Cl⁻ ions.
- Chlorine ends up with a full octet (8 electrons) after gaining an electron.
- Therefore, KCl follows the octet rule.
After analyzing each of the compounds, we determine that:
SF₆ (Sulfur Hexafluoride) demonstrates an exception to the octet rule because it has 12 electrons around the sulfur atom rather than 8.
So the correct answer is:
SF₆
