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Ch.10 - Chemical Bonding I: The Lewis Model
Chapter 10, Problem 40c

Write the Lewis symbols for the ions in each ionic compound. c. CaI2

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Step 1: Identify the ions present in the compound. In CaI2, the ions are Ca2+ and I-.
Step 2: Write the Lewis symbol for each ion. The Lewis symbol for an atom shows the chemical symbol for the element, and dots representing the valence electrons. For ions, the charge is also included.
Step 3: For Ca2+, the Lewis symbol is Ca with no dots around it, because it has lost its two valence electrons to achieve a stable electron configuration, and a 2+ charge is written as a superscript.
Step 4: For I-, the Lewis symbol is I with eight dots around it (four pairs), because it has gained one electron to achieve a stable electron configuration, and a 1- charge is written as a superscript.
Step 5: Combine the Lewis symbols for the ions to represent the ionic compound. In this case, the Lewis symbols for CaI2 would be Ca2+ and two I- ions.

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Key Concepts

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

Lewis Symbols

Lewis symbols, or Lewis dot structures, represent the valence electrons of an atom as dots around the element's symbol. This notation helps visualize how atoms bond and interact in chemical compounds. For ions, the Lewis symbol indicates the loss or gain of electrons, showing the resulting charge on the ion.
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Ionic Compounds

Ionic compounds are formed through the electrostatic attraction between positively charged cations and negatively charged anions. In the case of calcium iodide (CaI2), calcium (Ca) loses two electrons to become a Ca²⁺ cation, while each iodine (I) atom gains one electron to become I⁻ anions. The formula reflects the ratio of these ions in the compound.
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Charge Balance in Ionic Compounds

In ionic compounds, the total positive charge must balance the total negative charge to achieve electrical neutrality. For CaI2, the two I⁻ ions (each with a -1 charge) balance the +2 charge of the Ca²⁺ ion. Understanding this charge balance is crucial for correctly writing the formulas and Lewis symbols for the ions involved.
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