Chapter 13: Problem 71
Predict the electron pair geometry, the molecular shape, and the bond angle for a silane molecule, \(\mathrm{SiH}_{4}\), using VSEPR theory.
Short Answer
Expert verified
Silane (\(\mathrm{SiH}_{4}\)) has a tetrahedral shape with bond angles of \(109.5^\circ\).
Step by step solution
01
Identify the central atom
In the silane, \(\mathrm{SiH}_{4}\), the central atom is silicon (\(\mathrm{Si}\)). Silicon is less electronegative than hydrogen and can form four bonds with hydrogen atoms.
02
Calculate the number of valence electrons
Silicon (\(\mathrm{Si}\)) is in group 14 of the periodic table and has 4 valence electrons. Each hydrogen atom (\(\mathrm{H}\)) has 1 valence electron. Thus, the total number of valence electrons in \(\mathrm{SiH}_{4}\) is \(4 + 4 \times 1 = 8\).
03
Determine the number of electron pairs
The 8 valence electrons form 4 bonding pairs between silicon and the hydrogen atoms, considering each bond contains 2 electrons. No lone pairs are present on the silicon atom.
04
Predict the electron pair geometry
Since there are 4 electron pairs around the silicon atom and no lone pairs, VSEPR theory predicts that the electron pair geometry is tetrahedral. Each bond pair is arranged to be as far apart as possible from the others.
05
Determine the molecular shape
The electron pairs in the tetrahedral geometry are all bonding pairs with no lone pairs. Thus, the molecular shape mirrors the electron geometry, resulting in a tetrahedral molecular shape for \(\mathrm{SiH}_{4}\).
06
Calculate the bond angles
In a tetrahedral molecular shape, the bond angle between each bond is \(109.5^\circ\). This is the angle between each \(\mathrm{H}-\mathrm{Si}-\mathrm{H}\) bond in \(\mathrm{SiH}_{4}\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Silane Molecule
The silane molecule, represented as \( \mathrm{SiH}_{4} \), is an interesting compound that belongs to the family of silanes, compounds of silicon and hydrogen. In this molecule, silicon (Si) is the central atom, surrounded by four hydrogen atoms. This configuration is fundamental to understanding its chemical properties and behavior.
Silicon, like carbon, is capable of forming four covalent bonds because it has four valence electrons available for bonding. In \( \mathrm{SiH}_{4} \), each hydrogen atom, which has a single valence electron, shares its electron with silicon to form a covalent bond.
- This means there is a total of four \(\mathrm{Si}-\mathrm{H}\) bonds, allowing us to visualize the molecule as a silicon atom at the center with four hydrogen atoms at the corners.- Silane is significant in various applications, especially in materials science and chemistry, offering insights into complex chemical processes involving silicon.Understanding the silane molecule provides a basis for exploring its geometry and reactivity, contributing vastly to fields like organic chemistry and industrial applications.
Silicon, like carbon, is capable of forming four covalent bonds because it has four valence electrons available for bonding. In \( \mathrm{SiH}_{4} \), each hydrogen atom, which has a single valence electron, shares its electron with silicon to form a covalent bond.
- This means there is a total of four \(\mathrm{Si}-\mathrm{H}\) bonds, allowing us to visualize the molecule as a silicon atom at the center with four hydrogen atoms at the corners.- Silane is significant in various applications, especially in materials science and chemistry, offering insights into complex chemical processes involving silicon.Understanding the silane molecule provides a basis for exploring its geometry and reactivity, contributing vastly to fields like organic chemistry and industrial applications.
Electron Pair Geometry
Electron pair geometry refers to how electron pairs, including bonding and non-bonding pairs, are arranged around a central atom to minimize repulsion between them. In the case of silane, \( \mathrm{SiH}_{4} \), we focus on the electron pairs bonded to silicon.
Using VSEPR (Valence Shell Electron Pair Repulsion) theory, which postulates that electron pairs will arrange themselves as far apart as possible to minimize repulsion, we determine the electron pair geometry. A fundamental principle here is that electrons are negatively charged and repel one another.
- For \( \mathrm{SiH}_{4} \), silicon shares electrons with hydrogen to create four bonding pairs.- Since there are no lone pairs on the silicon atom, all of the electron pairs are involved in bonding.The VSEPR model predicts a tetrahedral electron pair geometry for the silane molecule. This arrangement ensures that all four \(\mathrm{Si}-\mathrm{H}\) bonds are equidistant, resulting in a minimized repulsive interaction between these electron pairs.
Using VSEPR (Valence Shell Electron Pair Repulsion) theory, which postulates that electron pairs will arrange themselves as far apart as possible to minimize repulsion, we determine the electron pair geometry. A fundamental principle here is that electrons are negatively charged and repel one another.
- For \( \mathrm{SiH}_{4} \), silicon shares electrons with hydrogen to create four bonding pairs.- Since there are no lone pairs on the silicon atom, all of the electron pairs are involved in bonding.The VSEPR model predicts a tetrahedral electron pair geometry for the silane molecule. This arrangement ensures that all four \(\mathrm{Si}-\mathrm{H}\) bonds are equidistant, resulting in a minimized repulsive interaction between these electron pairs.
Tetrahedral Molecular Shape
The molecular shape of a molecule is determined by the positions of the atoms around the central atom, influenced by the electron pair geometry. In the case of \( \mathrm{SiH}_{4} \), the molecular shape is described as tetrahedral, a vital concept in molecular geometry.
The tetrahedral shape occurs because the four bonds from the silicon atom distribute themselves as evenly as possible in three-dimensional space. Ensuring that the bond angle is approximately \( 109.5^\circ \), characteristic of a tetrahedral arrangement, helps in reducing repulsions between the bonds.
- In \( \mathrm{SiH}_{4} \), the absence of lone pairs aligns the molecular shape exactly with the electron pair geometry.- The tetrahedral shape is common in chemistry and is crucial for understanding the spatial arrangement of atoms in molecules, affecting properties like polarity and reactivity. Grasping the tetrahedral molecular shape offers insights into the nature of molecules that share this configuration and their interactions in various chemical reactions.
The tetrahedral shape occurs because the four bonds from the silicon atom distribute themselves as evenly as possible in three-dimensional space. Ensuring that the bond angle is approximately \( 109.5^\circ \), characteristic of a tetrahedral arrangement, helps in reducing repulsions between the bonds.
- In \( \mathrm{SiH}_{4} \), the absence of lone pairs aligns the molecular shape exactly with the electron pair geometry.- The tetrahedral shape is common in chemistry and is crucial for understanding the spatial arrangement of atoms in molecules, affecting properties like polarity and reactivity. Grasping the tetrahedral molecular shape offers insights into the nature of molecules that share this configuration and their interactions in various chemical reactions.
