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Ch.8 - Basic Concepts of Chemical Bonding
Chapter 8, Problem 14c

(c) Ti and Hf behave as though they possess the same number of valence electrons. Which of the subshells in the electron configuration of Hf behave as valence orbitals? Which behave as core orbitals?

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insert step 1> Start by writing the electron configuration for Hafnium (Hf). Hafnium has an atomic number of 72, so its electron configuration is: [Xe] 4f^{14} 5d^2 6s^2.
insert step 2> Identify the valence orbitals. Valence orbitals are the outermost orbitals that are involved in chemical bonding. For Hf, these are the 5d and 6s orbitals.
insert step 3> Identify the core orbitals. Core orbitals are the inner orbitals that are not involved in chemical bonding. For Hf, these include the 4f orbitals and all orbitals in the [Xe] core configuration.
insert step 4> Understand that the 4f orbitals are filled before the 5d orbitals, but they are considered core because they are not involved in bonding.
insert step 5> Conclude that for Hf, the 5d and 6s orbitals behave as valence orbitals, while the 4f orbitals and those in the [Xe] configuration behave as core orbitals.

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Key Concepts

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

Valence Electrons

Valence electrons are the outermost electrons of an atom and are crucial for chemical bonding and reactivity. They are found in the highest energy level (or shell) of an atom and determine how an element interacts with others. In transition metals like titanium (Ti) and hafnium (Hf), the d and s orbitals can contribute to the valence shell, influencing their chemical behavior.
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Electron Configuration

Electron configuration describes the distribution of electrons in an atom's orbitals. It is represented using a notation that indicates the energy levels and types of orbitals occupied by electrons. For Hf, the electron configuration is [Xe] 4f14 5d2 6s2, where the 5d and 6s orbitals are considered valence orbitals, while the 4f orbitals are core orbitals.
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Core vs. Valence Orbitals

Core orbitals are the inner electrons that are not involved in bonding and are typically closer to the nucleus, while valence orbitals are the outermost orbitals that participate in chemical reactions. In Hf, the 4f orbitals are core orbitals, and the 5d and 6s orbitals are valence orbitals, which play a significant role in its chemical properties and similarities to Ti.
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