Write Lewis structures for each molecule or ion. Use expanded octets as necessary. b. AsF₆^-

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Identify the total number of valence electrons in the AsF6^- ion. Arsenic (As) has 5 valence electrons, each fluorine (F) has 7 valence electrons, and there is an additional electron due to the negative charge.

Calculate the total number of valence electrons: 5 (from As) + 6*7 (from six F atoms) + 1 (extra electron for the negative charge).

Place the arsenic atom in the center and arrange the six fluorine atoms around it, as fluorine is more electronegative and typically forms single bonds.

Distribute the electrons by forming single bonds between the central arsenic atom and each fluorine atom. Each bond uses 2 electrons.

Distribute the remaining electrons to satisfy the octet rule for each fluorine atom. If there are any remaining electrons, place them on the central arsenic atom, allowing for an expanded octet.

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Key Concepts

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

Lewis Structures

Lewis structures are diagrams that represent the bonding between atoms in a molecule and the lone pairs of electrons that may exist. They use dots to represent valence electrons and lines to represent bonds between atoms. Understanding how to draw Lewis structures is essential for visualizing molecular geometry and predicting reactivity.

Expanded Octet

An expanded octet refers to the ability of certain elements, particularly those in the third period and beyond, to accommodate more than eight electrons in their valence shell. This occurs because these elements have d orbitals available for bonding. Recognizing when to apply expanded octets is crucial for accurately representing molecules like AsF6-.

Formal Charge

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. It helps in determining the most stable Lewis structure by minimizing formal charges across the molecule. Understanding formal charge is vital for evaluating the validity of different Lewis structures.