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Ch.2 - Atoms, Molecules, and Ions
Chapter 2, Problem 66a

Predict whether each of the following compounds is molecular or ionic. a. PF5

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1
Identify the elements involved in the compound: PF₅ consists of phosphorus (P) and fluorine (F).
Determine the type of elements: Phosphorus is a non-metal, and fluorine is also a non-metal.
Recall the general rule: Compounds formed between non-metals are typically molecular (covalent), while compounds formed between metals and non-metals are typically ionic.
Since both phosphorus and fluorine are non-metals, PF₅ is likely to be a molecular compound.
Conclude that PF₅ is a molecular compound because it is formed by the sharing of electrons between non-metal atoms.

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Key Concepts

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

Ionic vs. Molecular Compounds

Ionic compounds are formed from the electrostatic attraction between positively and negatively charged ions, typically involving a metal and a nonmetal. In contrast, molecular compounds consist of molecules formed by covalent bonds, where atoms share electrons, usually involving nonmetals. Understanding the distinction helps in predicting the properties and structures of compounds.
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Electronegativity

Electronegativity is a measure of an atom's ability to attract and hold onto electrons in a bond. In general, a large difference in electronegativity between two atoms indicates an ionic bond, while a small difference suggests a covalent bond. For example, in PF5, the electronegativity of phosphorus and fluorine can help determine the nature of the compound.
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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 are useful for visualizing how atoms are connected and can help predict whether a compound is molecular or ionic. Drawing the Lewis structure for PF5 reveals its molecular nature, as it consists of covalent bonds between phosphorus and fluorine atoms.
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