Consider the following XF4 ions: PF4-, BrF4-, ClF4+, and AlF4-. (c) Which of the ions will have an octahedral electron-domain geometry?

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Identify the central atom in each ion: P in PF4-, Br in BrF4-, Cl in ClF4+, and Al in AlF4-.

Determine the number of valence electrons for each central atom and add or subtract electrons based on the ion's charge.

Add one electron for each fluorine atom bonded to the central atom, as each F forms a single bond.

Calculate the total number of electron domains (regions of electron density) around the central atom, including both bonding pairs and lone pairs.

Identify the electron-domain geometry based on the total number of electron domains: 6 domains correspond to an octahedral geometry.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Electron-Domain Geometry

Electron-domain geometry refers to the spatial arrangement of electron pairs around a central atom, which can include bonding pairs and lone pairs. The VSEPR (Valence Shell Electron Pair Repulsion) theory is used to predict this geometry, where electron pairs repel each other and adopt an arrangement that minimizes repulsion. Common geometries include linear, trigonal planar, tetrahedral, and octahedral.

Octahedral Geometry

An octahedral geometry occurs when a central atom is surrounded by six electron domains, resulting in a symmetrical arrangement of atoms or groups at the corners of an octahedron. This geometry typically arises in molecules with six bonding pairs and no lone pairs, or in cases where lone pairs are present but do not alter the overall shape significantly.

Formal Charge and Stability

Formal charge is a theoretical charge assigned to an atom in a molecule, calculated based on the number of valence electrons, the number of non-bonding electrons, and half the number of bonding electrons. Understanding formal charge helps predict the most stable structure of a molecule, as lower formal charges on atoms generally indicate greater stability. This concept is crucial when determining the most likely electron-domain geometry for ions.

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Formal Charge

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Textbook Question

Ammonia, NH3, reacts with incredibly strong bases to produce the amide ion, NH2-. Ammonia can also react with acids to produce the ammonium ion, NH4+. (a) Which species (amide ion, ammonia, or ammonium ion) has the largest H¬N¬H bond angle? (b) Which species has the smallest H¬N¬H bond angle?

Textbook Question

Consider the following XF₄ ions: PF₄^-, BrF₄^-, ClF₄⁺, and AlF₄^-. (a) Which of the ions have more than an octet of electrons around the central atom?

Textbook Question

Which of the following statements are true?

i. The overall dipole moment of a molecule is the vector sum of its individual bond dipoles.

ii. If atoms A and B in an AB𝑛 molecule have different electronegativities, then the AB𝑛 molecule must have a nonzero dipole moment.

iii. The bond dipoles in a tetrahedral AB4 molecule cancel one another.