Question

What type of solid will each of the following substances form? a. \(\mathrm{CO}_{2}\) b. \(\mathrm{SiO}_{2}\) c. \(\mathrm{Si}\) d. \(\mathrm{CH}_{4}\) e. \(\mathrm{Ru}\) f. \(\mathrm{I}_{2}\) g. \(\mathrm{KBr}\) h. \(\mathrm{H}_{2} \mathrm{O}\) i. \(\mathrm{NaOH}\) j. \(\mathrm{U}\) k. \(\mathrm{CaCO}_{3}\) I. \(\mathrm{PH}_{3}\)

Short answer

a. Molecular solid b. Covalent solid c. Covalent solid d. Molecular solid e. Metallic solid f. Molecular solid g. Ionic solid h. Molecular solid i. Ionic solid j. Metallic solid k. Ionic solid l. Molecular solid

Step-by-step solution

a. CO2

\(\mathrm{CO}_{2}\) is a covalent compound, consisting of a central carbon atom double bonded to two oxygen atoms. This forms a linear molecule. Since \(\mathrm{CO}_{2}\) consists of discrete molecules held together by weak London dispersion forces, it forms a molecular solid.

b. SiO2

\(\mathrm{SiO}_{2}\) is a covalent compound made up of a silicon atom bonded to two oxygen atoms. In a solid state, each of these atoms continues to bond covalently with other atoms, forming an extended three-dimensional network of covalent bonds. Thus, \(\mathrm{SiO}_{2}\) forms a covalent (or network) solid.

c. Si

Silicon is a pure element with covalent bonding between its atoms. It forms a crystal structure similar to diamond, consisting of a network of covalently bonded silicon atoms. Thus, silicon forms a covalent solid.

d. CH4

Methane, \(\mathrm{CH}_{4}\), is a molecular compound composed of carbon covalently bonded to four hydrogen atoms. In methane's solid form, it consists of discrete molecules held together by weak London dispersion forces, forming a molecular solid.

e. Ru

Ruthenium (Ru) is a metal and forms metallic bonds, which involves the sharing of free electrons among a lattice of metal atoms. Therefore, ruthenium forms a metallic solid.

f. I2

Iodine (I2) is a diatomic molecule held together by a covalent bond. In its solid form, discrete iodine molecules are held together by weak London dispersion forces. Therefore, iodine forms a molecular solid.

g. KBr

\(\mathrm{KBr}\) is an ionic compound, formed by the transfer of an electron from potassium to bromine. In the solid state, potassium and bromine ions are held together by strong electrostatic forces (ionic bonds) in a crystal lattice, making it an ionic solid.

h. H2O

When water (\(\mathrm{H}_{2} \mathrm{O}\)) is in the solid state (ice), it forms a molecular solid. In ice, the water molecules are held together by hydrogen bonds, which are stronger than London dispersion forces but weaker compared to covalent or ionic bonds.

i. NaOH

Sodium hydroxide (\(\mathrm{NaOH}\)) is an ionic compound that consists of sodium ions and hydroxide ions. These ions are held together by strong electrostatic forces (ionic bonds) in a crystal lattice, making sodium hydroxide an ionic solid.

j. U

Uranium (U) is a metal and forms metallic bonds, in which free electrons are shared among a lattice of metal ions. Therefore, uranium forms a metallic solid.

k. CaCO3

Calcium carbonate (\(\mathrm{CaCO}_{3}\)) is an ionic compound, consisting of calcium, carbon, and oxygen ions. In the solid state, these ions are held together by strong electrostatic forces (ionic bonds) in a crystal lattice, making calcium carbonate an ionic solid.

l. PH3

Phosphine (\(\mathrm{PH}_{3}\)) is a molecular compound composed of phosphorus covalently bonded to three hydrogen atoms. In phosphine's solid form, it consists of discrete molecules held together by weak London dispersion forces, forming a molecular solid.

Key concepts

Covalent compounds

Covalent compounds represent a class of compounds where the atoms involved share electrons to achieve stability. This sharing of electrons forms covalent bonds, which can vary in strength based on the nature of the elements involved and the number of shared electrons.

• Carbon Dioxide ( ext {CO}_{2} ): CO2 is a simple covalent molecule where each carbon atom is double-bonded to two oxygen atoms, forming a linear structure. Its solid form is classified as a molecular solid due to weak intermolecular forces holding the molecules together.
• Silicon Dioxide ( ext {SiO}_{2} ): Differing from CO2, SiO2 forms an extensive network covalent solid. Each silicon atom is bonded to four oxygens, creating a robust three-dimensional lattice.
• Silicon (Si): Pure silicon forms a covalent network solid, similar to diamond, where each atom is covalently bonded to others in a tetrahedral structure, making it very hard and resilient.

Ionic compounds

Ionic compounds arise from the electrostatic interaction between ions, usually a metal and a non-metal, forming when electrons are completely transferred from one atom to another, creating charged particles.

• Potassium Bromide ( ext {KBr} ): It forms when potassium transfers an electron to bromine, creating a lattice of K+ and Br- ions that are held together by strong electrostatic forces in a solid form known as an ionic solid.
• Sodium Hydroxide ( ext {NaOH} ): Similarly, NaOH consists of Na+ and OH- ions. When solid, these ions are arranged in a crystalline lattice.
• Calcium Carbonate ( ext {CaCO}_{3} ): Here, calcium ions and carbonate ions are tightly held together in an ionic bond, making it a common ionic solid found in various minerals.

Molecular solids

Molecular solids are characterized by discrete molecules held together by relatively weak forces such as London dispersion, dipole-dipole interactions, or hydrogen bonds.

• Water ( ext {H}_{2} ext{O} ): When frozen, water molecules are held together by hydrogen bonds, forming a crystalline molecular solid known as ice. These bonds are stronger than other intermolecular forces but are weaker than covalent or ionic bonds.
• Iodine ( ext {I}_{2} ): Solid iodine consists of ext {I}_{2} molecules held together by London dispersion forces, making it a molecular solid.
• Methane ( ext {CH}_{4} ): In its solid state, the methane's molecules are loosely packed and held by weak London dispersion forces.

Metallic solids

Metallic solids are formed by metal elements where atoms are arranged in a lattice structure, and electrons move freely around, creating a "sea of electrons." This allows metallic solids to conduct electricity and heat efficiently.

• Ruthenium ( ext {Ru} ): As a metal, ruthenium forms a solid with metallic bonds, where its atomic lattice is surrounded by a cloud of shared electrons.
• Uranium ( ext {U} ): Uranium similarly forms metallic bonds, allowing for its extensive use in energy applications due to its conductivity and malleability.