Problem 47 - Chemistry The Molecular Science

Question

Classify each of these solids as ionic, metallic, molecular, network, or amorphous. (a) Tetraphosphorus decaoxide (b) Brass (c) Ammonium phosphate (d) Graphite

Step-by-Step Solution

Answer

(a) Molecular, (b) Metallic, (c) Ionic, (d) Network.

Step 1: Identify Tetraphosphorus Decaoxide Type

Tetraphosphorus decaoxide (\(P_4O_{10}\)) is a compound composed of nonmetal atoms. It has a covalent structure where phosphorus and oxygen atoms are connected through covalent bonds, forming a discrete molecular compound. Thus, tetraphosphorus decaoxide is classified as a molecular solid.

Step 2: Analyze Brass Composition

Brass is an alloy predominantly made of copper and zinc. It consists of metallic bonds where positively charged metal ions are surrounded by a sea of delocalized electrons. This electron sea allows for properties such as conductivity and malleability. Brass is classified as a metallic solid.

Step 3: Classify Ammonium Phosphate

Ammonium phosphate, \((NH_4)_3PO_4\), is composed of ammonium ions \((NH_4^+)\) and phosphate ions \((PO_4^{3-})\). These ions are held together by ionic bonds, a characteristic of ionic solids. Thus, ammonium phosphate is classified as an ionic solid.

Step 4: Determine Graphite Structure

Graphite is composed of layers of carbon atoms arranged in hexagonal patterns. Each carbon atom is bonded to three others in a planar configuration, forming layers that can slide over each other due to weak forces between them. These layers are essentially a network of covalent bonds, classifying graphite as a network solid.

Key Concepts

Molecular Solids

Molecular solids are characterized by distinct, small molecules that are held together by relatively weak forces, such as van der Waals forces, hydrogen bonds, or dipole-dipole interactions. These solids are typically composed of nonmetals and have covalent bonds within the individual molecules. However, the forces between these molecules are what determine their solid form.
Examples of molecular solids include ice, solid carbon dioxide ( CO_2 ), and tetraphosphorus decaoxide ( P_4O_{10} ). These solids often exhibit low melting and boiling points due to the weak intermolecular forces holding them together. Molecular solids are generally poor conductors of electricity.
Some key characteristics of molecular solids are:

• Low melting and boiling points.
• Poor electrical conductivity.
• Can be soft or brittle.

Metallic Solids

Metallic solids are formed by metal elements where atoms share a pool of delocalized electrons, often referred to as a "sea of electrons." This electron sharing grants metallic solids their characteristic traits, such as electrical and thermal conductivity, luster, and malleability.
The structure of metallic solids allows the electron cloud to move freely, hence permitting heat and electric current to pass through easily. Alloys, such as brass (a mixture of copper and zinc), are metallic solids that combine different metals to enhance properties like strength or corrosion resistance.
Important features of metallic solids include:

• High electrical and thermal conductivity.
• Malleability and ductility.
• Metallic luster.

Ionic Solids

Ionic solids consist of ions arranged in a lattice structure held together by strong electrostatic forces known as ionic bonds. They are typically formed between metals and nonmetals, resulting in the formation of positive and negative ions.
Common examples include table salt ( NaCl ) and ammonium phosphate ( (NH_4)_3PO_4 ). Ionic solids are known for their high melting and boiling points due to the strength of their ionic bonds. When dissolved in water or melted, they conduct electricity as the ions are free to move, but in their solid state, they do not conduct electricity.
Characteristics of ionic solids include:

• High melting and boiling points.
• Brittle and hard in nature.
• Electrical conductivity in molten or dissolved form.

Network Solids

Network solids are composed of atoms connected in a continuous network extending throughout the material. These atoms are bonded covalently, forming a structure where the entire solid can be considered one large molecule.
Graphite and diamond are classic examples of network solids, showcasing their diverse properties. Graphite has layers of carbon atoms bonded in hexagonal arrays, allowing them to slide and making graphite a good lubricant. Its network allows it to conduct electricity, unlike many network solids.
Network solids are characterized by:

• Very high melting and boiling points.
• Typically hard and strong.
• Poor electrical conductivity, except for materials like graphite.