Question

Silicon has a limited capacity to form linear, \(\mathrm{Si}-\mathrm{Si}\) bonded structures similar to those formed by carbon. (a) Predict the molecular formula of a hydride of silicon that contains a chain of three silicon atoms. (b) Write a balanced equation for the reaction between oxygen and the compound you predicted in part (a).

Short answer

(a) The molecular formula of the silicon hydride with a chain of three silicon atoms is \(Si_3H_8\). (b) The balanced equation for the reaction between the silicon hydride and oxygen is: \(Si_3H_8 + 8O_2 \rightarrow 3SiO_2 + 4H_2O\).

Step-by-step solution

(a) Predicting the molecular formula of the silicon hydride

To predict the molecular formula of a silicon hydride with a chain of three silicon atoms, we first need to identify the number of hydrogen atoms that can bond with each silicon atom. Silicon belongs to Group 14 in the periodic table and has four valence electrons. To achieve a stable octet configuration, a silicon atom forms four covalent bonds. Since we have a chain of three silicon atoms, we need to consider how the hydrogen atoms can bond with the silicon atoms. For the two silicon atoms at the ends of the chain, each can form three covalent bonds with hydrogen atoms while the remaining one bond will be with another silicon atom. The middle silicon atom will have two bonds with the adjacent silicon atoms, which means it can form two covalent bonds with hydrogen atoms. So the molecular formula of the silicon hydride will be \(Si_3H_8\).

(b) Writing the balanced reaction equation with oxygen

To write a balanced equation for the reaction between the silicon hydride (\(Si_3H_8\)) and oxygen, first, consider the products that will be formed. The silicon hydride will react with oxygen to form silicon dioxide (\(SiO_2\)) and water (\(H_2O\)) as products. Now, we need to balance the equation by making sure that the number of atoms of each element is equal on both sides of the equation. Our initial unbalanced equation is: \[Si_3H_8 + O_2 \rightarrow SiO_2 + H_2O\] To balance the equation, we'll first balance the silicon atoms: \[Si_3H_8 + O_2 \rightarrow 3SiO_2 + H_2O\] Next, we'll balance the hydrogen atoms: \[Si_3H_8 + O_2 \rightarrow 3SiO_2 + 4H_2O\] Finally, we'll balance the oxygen atoms: \[Si_3H_8 + 8O_2 \rightarrow 3SiO_2 + 4H_2O\] Now, the balanced equation for the reaction between the silicon hydride and oxygen is as follows: \[Si_3H_8 + 8O_2 \rightarrow 3SiO_2 + 4H_2O\]

Key concepts

Silicon Hydrides

Silicon hydrides are fascinating compounds primarily composed of silicon and hydrogen. Also known as silanes, these compounds showcase the unique bonding capabilities of silicon, which closely resemble those of carbon, albeit with some distinct differences. Unlike carbon, silicon has a larger atomic radius. This reduces the overlap between atomic orbitals, influencing its bonding properties and limiting its ability to form multiple bonds efficiently.

• The simplest form of a silicon hydride is monosilane, with the chemical formula SiH₄.
• A key feature of silicon hydrides is that they can form chains, resembling the carbon chains in hydrocarbons.
• These chains, however, are typically less stable than their carbon counterparts due to silicon's weaker Si-Si bond strengths.

Predicting the molecular formula of a silicon hydride involves understanding the valency of silicon, which is four. In the example exercise, a chain of three silicon atoms is considered. Silicon can form four covalent bonds, and by strategically bonding with hydrogen, various silanes can be synthesized such as Si₃H₈.

Chemical Bonding

Chemical bonding is the force that holds atoms together in compounds. For silicon hydrides, these bonds are primarily covalent. Understanding how these bonds form and their properties is crucial in predicting the behavior and reactivity of silicon-containing compounds.

• Silicon atoms have four valence electrons which they share with hydrogen atoms to fulfill their octet.
• The Si-Si bond is essential in creating extended silicon structures, which can be linear or branched, though these structures are typically less robust than carbon-based analogs.
• The presence of unpaired electrons and the ability to form multiple bonds play a significant role in the reactivity of silicon hydrides.

Bond strength and bond angles are critical factors when examining how these molecules are structured and how they interact with other substances. The unique characteristics of silicon's bonding lead to different chemical and physical properties when compared to carbon-containing compounds.

Balanced Chemical Equations

Writing balanced chemical equations is fundamental to understanding chemical reactions. It ensures that the law of conservation of mass is satisfied, illustrating that atoms are neither created nor destroyed in a reaction.

• A balanced chemical equation provides the correct proportion of reactants and products involved in the chemical reaction.
• In the case of silicon hydride reacting with oxygen, the products are silicon dioxide and water.
• The balancing process involves equalizing the number of silicon, hydrogen, and oxygen atoms on both sides of the equation.

The given balanced equation \[Si_3H_8 + 8O_2 \rightarrow 3SiO_2 + 4H_2O\] indicates that three molecules of silicon dioxide and four molecules of water are formed from one molecule of silane and eight molecules of oxygen. This balance helps predict the quantities of substances consumed and produced.

Oxidation Reactions

Oxidation reactions are chemical processes involving the transfer of electrons, resulting in an increase in the oxidation state of a molecule, atom, or ion. In silicon chemistry, oxidation is particularly significant when silicon hydrides react with oxygen, as presented in the example.

• When silicon hydrides oxidize, the silicon atoms form silicon dioxide (\(SiO_2\)
• This type of reaction is exothermic, meaning it releases energy, usually in the form of heat.
• Understanding these reactions is crucial for industrial and environmental applications, since silicon dioxide forms a protective coating on silicon, preventing further oxidation.

Oxidation is pivotal in silicon's application in technology, particularly in silicon-based semiconductors, where oxide layers play a crucial role in device functionality and stability. Recognizing how silicon transitions in oxidation reactions can lead to developing new materials and technological advancements.