Ch.2 - Atoms, Molecules, and Ions

Problem 58e

Chapter 2, Problem 58e

Using the periodic table, predict the charge of the most stable ion of the following elements: e. Se

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Identify the group number of the element Selenium (Se) on the periodic table. Selenium is located in Group 16.

Recall that elements in Group 16 typically form ions with a charge of -2. This is because they tend to gain two electrons to achieve a full outer shell, similar to the nearest noble gas configuration.

Understand that the most stable ion of an element is often the one that achieves a noble gas electron configuration. For Selenium, gaining two electrons will result in the electron configuration of Krypton, a noble gas.

Conclude that the most stable ion of Selenium (Se) is Se²⁻, as it achieves a stable electron configuration by gaining two electrons.

Verify your prediction by considering the general trend: elements in Group 16, such as Oxygen and Sulfur, also form ions with a -2 charge, supporting the prediction for Selenium.

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Key Concepts

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

Periodic Table and Group Trends

The periodic table organizes elements based on their atomic number and electron configuration, revealing trends in properties such as electronegativity and ionization energy. Elements in the same group (column) typically exhibit similar chemical behavior, including the charge of their most stable ions. For example, elements in Group 16, like selenium (Se), tend to gain electrons to achieve a stable octet, leading to a common charge of -2.

Ion Formation and Stability

Ions are formed when atoms gain or lose electrons to achieve a more stable electronic configuration, often resembling that of the nearest noble gas. The stability of an ion is influenced by its charge and the energy required to form it. For selenium, gaining two electrons to form a Se²⁻ ion is energetically favorable, as it completes its valence shell, making it the most stable ion.

Electronegativity and Electron Affinity

Electronegativity is a measure of an atom's ability to attract and hold onto electrons, while electron affinity refers to the energy change when an electron is added to a neutral atom. Elements with high electronegativity, like selenium, have a strong tendency to gain electrons, which contributes to the formation of negatively charged ions. This property is crucial for predicting the charge of ions formed by elements in chemical reactions.

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Electron Affinity

Related Practice

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Fill in the gaps in the following table:

Symbol 31P3-

Protons 34 50

Neutrons 45 69 118

Electrons 46 76

Net charge 2- 3+

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