Final answer:
The student's question pertains to identifying octet rule violations in a molecular formula. These may involve odd-electron molecules, electron-deficient molecules, or expanded valence shell molecules, like in the molecule BH3, Borane, where boron has less than eight valence electrons.
Step-by-step explanation:
The question relates to spotting octet rule mistakes in a molecular formula. The octet rule, a key concept in Chemistry, states that atoms tend to bond in such a way that they have eight electrons in their valence shell, giving them the same electronic configuration as a noble gas. However, there are exceptions to this rule, which are important for correctly drawing Lewis structures for molecules and ions. The three main types of exceptions are:
- Odd-electron molecules: These cannot satisfy the octet rule because they have an odd number of valence electrons, making it impossible to form pairs that complete an octet for each atom.
- Electron-deficient molecules: Atoms like beryllium, aluminum, and boron often form compounds where they have fewer than eight electrons in their valence shell, such as in BH3 (Borane).
- Expanded valence shell molecules: Atoms in periods 3 and beyond of the periodic table can have more than eight valence electrons due to available d-orbitals, which is not possible for second-row elements.
As an example, a molecule that violates the octet rule would be BH3, Borane, where the boron atom has only six valence electrons instead of the usual eight.