Question

Describe the structural units in (a) C (graphite) (b) \(S_{i} C\) (c) \(\mathrm{FeCl}_{2}\) (d) \(\mathrm{C}_{2} \mathrm{H}_{2}\)

Short answer

In this exercise, we analyzed the structural units of four different compounds: (a) Graphite (Carbon): Graphite has a layered structure consisting of planar hexagonal rings of carbon atoms held together by weak van der Waals forces. (b) Silicon Carbide (SiC): Silicon carbide has a three-dimensional lattice structure with each silicon atom bonded tetrahedrally to four carbon atoms, and each carbon atom bonded tetrahedrally to four silicon atoms. (c) Iron(II) Chloride (FeCl2): Iron(II) chloride is an ionic compound consisting of Fe2+ cations and Cl- anions in an extended three-dimensional lattice structure, with each iron ion surrounded by six chloride ions in an octahedral arrangement. (d) Ethyne (C2H2): Ethyne is a simple organic molecule with a linear structure and a triple bond between two carbon atoms (C≡C), with each carbon atom also bonded to a hydrogen atom. The carbon atoms are sp-hybridized.

Step-by-step solution

(a) Graphite (Carbon)

Graphite is an allotrope of carbon and has a layered structure. Each carbon atom in graphite is covalently bonded to three other carbon atoms, forming planar hexagonal rings. These layers are held together by weak van der Waals forces, which allow the layers to slide past one another, making graphite a good lubricant and giving it its characteristic slippery feel.

(b) Silicon Carbide (SiC)

Silicon carbide (SiC) is a covalent compound in which each silicon atom is tetrahedrally bonded to four carbon atoms, and each carbon atom is tetrahedrally bonded to four silicon atoms. This arrangement forms a three-dimensional lattice structure which is very strong and hard. Silicon carbide is commonly used as an abrasive material due to its hardness.

(c) Iron(II) Chloride (FeCl2)

Iron(II) chloride (FeCl2) is an ionic compound composed of Fe2+ cations and Cl- anions. The positively charged iron ions are surrounded by six negatively charged chloride ions in an octahedral arrangement. The chloride ions are also surrounded by a number of iron ions in their coordination sphere. This causes the formation of an extended three-dimensional lattice structure in the solid state.

(d) Ethyne (C2H2)

Ethyne, also known as acetylene, is a simple organic molecule with the molecular formula C2H2. The molecule has a linear structure with a triple bond between the two carbon atoms (C≡C) and single bonds connecting each carbon atom to a hydrogen atom. The carbon atoms are sp-hybridized.

Key concepts

Graphite Structure

Graphite, an allotrope of carbon, is renowned for its unique structure. Each carbon atom is covalently bonded to three others, creating a pattern of hexagonal rings reminiscent of a honeycomb. These planar sheets stack atop each other but are not tightly bound; rather, they're held together by subtle van der Waals forces.

These forces are relatively weak, which makes graphite's layers able to slide over one another, giving graphite its characteristic slippery touch. This makes it an ideal substance for applications like pencil leads and as a dry lubricant.

• Layered configuration of carbon atoms
• Hexagonal rings in planar sheets
• Weak van der Waals forces between layers
• Highly functional in various applications due to its unique properties

Silicon Carbide Lattice

Silicon carbide, represented as SiC, is a compound characterized by a robust and intricate lattice structure. In this network, each silicon atom is tetrahedrally connected to four carbon atoms, and vice versa – a symmetrical and sturdy configuration.

The resulting three-dimensional pattern is responsible for the material's exceptional hardness and thermal conductivity. These properties are why silicon carbide is often utilized in high-stress scenarios such as abrasive materials and in high-performance braking systems.

• Tetrahedral bonding of silicon and carbon atoms
• Three-dimensional lattice structure
• Marked by extreme hardness
• Integral in industrial applications requiring durability

Iron(II) Chloride Bonding

Iron(II) chloride, known chemically as FeCl2, consists of a lattice structure that arises from ionic bonding. The iron ions (Fe2+) form an octahedral geometry, surrounded by six chloride ions (Cl-), which also associate with neighboring iron ions.

This arrangement creates a continuous network that extends throughout the solid, contributing to the stability and rigidity of the compound. Iron(II) chloride exhibits properties typical of ionic compounds, such as high melting points and the ability to dissolve in water producing electrolyte solutions.

• Octahedral coordination of Fe2+ and Cl- ions
• Extended three-dimensional lattice
• Characteristic ionic compound attributes

Ethyne Molecular Configuration

Ethyne, or acetylene as it's more commonly known, is the simplest alkyne with a pronounced linear molecular arrangement. The carbon atoms in ethyne are sp-hybridized and connected by a triple bond, denoted as C≡C.

Each carbon atom also bonds with a hydrogen atom. This molecular layout is not just fundamental for ethyne’s chemical properties but also for academic discussions on hybridization and molecular geometry.

• Carbon atoms linked by a triple bond
• Linear structure with sp-hybridization
• Forms the foundational structure for alkynes