Question

Describe the bonding scheme of the \(\mathrm{AsH}_{3}\) molecule in terms of hybridization.

Short answer

\(\text{AsH}_3\) has \(sp^3\) hybridization with a trigonal pyramidal shape due to a lone pair.

Step-by-step solution

Understanding the Atom and Its Valence Electrons

To describe the hybridization in \(\text{AsH}_3\), we begin by identifying the central atom, which is arsenic (As). Arsenic belongs to Group 15 of the periodic table and has a ground state electron configuration of \([ ext{Ar}] 3d^{10} 4s^2 4p^3\). Among these, the \(4s\) and \(4p\) orbitals are the valence electrons.

Determining the Type of Hybridization

Based on the need to form bonds with three hydrogen atoms, arsenic has three unpaired electrons in its \(4p\) orbitals. For \(\text{AsH}_3\), the arsenic atom will use \(sp^3\) hybridization, where one \(4s\) orbital and three \(4p\) orbitals mix to form four equivalent \(sp^3\) hybrid orbitals. However, since three \(sp^3\) orbitals are used for bonding with hydrogen, one remains as a lone pair.

Assessing Bond Formation

For each \(\text{As-H}\) bond, the \(sp^3\) hybrid orbitals overlap with the \(1s\) orbitals of hydrogen atoms, forming sigma (\(\sigma\)) bonds. With the three \(sp^3\) hybrid orbitals engaging in bonding and one holding a lone pair, the molecule forms a pyramidal shape.

Concluding the Hybridization Description

Therefore, \(\text{AsH}_3\) has an \(sp^3\) hybridization at the arsenic atom with a lone pair present, resulting in a trigonal pyramidal molecular geometry.

Key concepts

Valence Electrons

Valence electrons play a key role in determining how atoms bond and interact with each other. These electrons are located in the outermost shell of an atom and are crucial because they participate in forming chemical bonds. For arsenic, which is found in Group 15 of the periodic table, the ground state electron configuration is \([\text{Ar}] 3d^{10} 4s^2 4p^3\).
\(\
\)The valence electrons for arsenic are those in the 4s and 4p orbitals, totaling five valence electrons. Of these, the three 4p electrons are unpaired and available for bonding. This availability plays a vital role in hybridization, allowing arsenic to form bonds with hydrogen atoms to create the \(\text{AsH}_3\) molecule. Understanding valence electrons helps in predicting molecular bonding and the resulting shape of molecules.

Sigma Bonds

Sigma bonds, represented as \(\sigma\) bonds, are the strongest type of covalent bond and occur when orbitals overlap directly between two atomic nuclei. In the \(\text{AsH}_3\) molecule, sigma bonds form when the \(sp^3\) hybrid orbitals of arsenic overlap with the 1s orbitals of hydrogen atoms.
\(
\)Each \(\text{As-H}\) connection is a single sigma bond, ensuring that the bond is strong and the atoms are firmly held together in the molecule. The configuration of these bonds is a result of hybridization, where the mixing of orbitals allows for optimal overlap, directly contributing to the molecule's stability and structure. Remember, sigma bonds are distinct from pi bonds, which involve lateral overlapping and are typically found in multiple bond scenarios.

Molecular Geometry

Molecular geometry refers to the three-dimensional arrangement of atoms within a molecule. The shape of a molecule influences many of its physical and chemical properties. In the case of \(\text{AsH}_3\), the molecule adopts a trigonal pyramidal shape.
\(
\)This geometry arises from the \(sp^3\) hybridization of arsenic, where three hybrid orbitals form bonds with hydrogen, and one orbital holds a lone pair. The repulsion between the lone pair and the bonding pairs results in the pyramidal shape, deviating from a perfect tetrahedron. Understanding this geometry is essential as it affects polarity and intermolecular interactions, critical factors in chemical reactivity and biological activity.

Periodic Table Groups

The periodic table is organized into groups, or columns, which classify elements with similar properties and valence electron configurations. Arsenic, being part of Group 15, shares characteristics with nitrogen, phosphorus, antimony, and bismuth.
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\)Elements in Group 15 typically have five valence electrons, making them predisposed to forming three bonds and sometimes containing lone pairs, as seen in arsenic's involvement in \(\text{AsH}_3\).
\(
\)These groups help predict how an element will behave in a reaction, its potential bonding patterns, and its general reactivity. By understanding where an element resides within the periodic table, we gain insights into its chemical properties, which assists in predicting outcomes in molecular bonding and hybridization.