Question

Give two examples of nonmetallic elements that have allotropes. Name those elements and describe the allotropes of each.

Short answer

Carbon and phosphorus have allotropes, including diamond/graphite for carbon and white/red phosphorus.

Step-by-step solution

Identify Element #1 with Allotropes

The first nonmetallic element with allotropes is carbon. Carbon has several allotropes, including diamond, graphite, and fullerene. Each allotrope has different properties due to the unique arrangements of carbon atoms.

Describe Allotropes of Carbon

Diamond is an allotrope of carbon where each carbon atom is bonded to four other carbon atoms in a tetrahedral arrangement, creating a very hard structure. Graphite, on the other hand, has carbon atoms arranged in layers with each atom bonding to three other atoms, leading to softer and slippery characteristics. Fullerenes are molecules composed entirely of carbon, taking the form of a hollow sphere, ellipsoid, or tube.

Identify Element #2 with Allotropes

The second nonmetallic element with allotropes is phosphorus. Its primary allotropes include white phosphorus and red phosphorus, which vary widely in properties and structures.

Describe Allotropes of Phosphorus

White phosphorus consists of P4 tetrahedra and is more reactive, often stored under water to prevent exposure to air. Red phosphorus, on the other hand, is a polymer-like network and is more stable compared to white phosphorus, used commonly in safety matches.

Key concepts

Nonmetallic Elements

Nonmetallic elements are a diverse group characterized by their lack of metallic properties. These elements often have high electronegativities and are poor conductors of electricity. They are vital for life and the environment. Nonmetals gain electrons easily and form negative ions during chemical reactions. This is in contrast to metals, which tend to lose electrons. Nonmetals can exist in various physical states at room temperature:

• Gases: such as oxygen and nitrogen.
• Liquids: such as bromine.
• Solids: such as sulfur.

Nonmetals can form allotropes, which are different structural forms of the same element. Each form has distinct physical and chemical properties due to variations in the arrangement of atoms.

Carbon Allotropes

Carbon is a well-known nonmetallic element with several allotropes. Each allotrope exhibits unique properties due to different atomic structures.

- **Diamond**: In diamond, carbon atoms are bonded tetrahedrally, creating a strong, hard structure. This arrangement results in a very high melting point and unparalleled hardness among natural and synthetic materials.
- **Graphite**: Here, carbon atoms are arranged in layers, with atoms forming a hexagonal network within each layer. This bonding provides graphite with its slippery feel, making it useful as a lubricant, and its ability to conduct electricity due to free-moving electrons.
- **Fullerenes**: These are molecules composed entirely of carbon, forming hollow structures like spheres or tubes. Fullerenes exhibit a range of properties that make them useful in nanotechnology and materials science.

Phosphorus Allotropes

Phosphorus is another nonmetal that comes in several allotropes, each with different properties based on its atomic structure.

- **White phosphorus**: Comprises P4 tetrahedral units. This allotrope is highly reactive and flammable, often stored under water or in inert gases to prevent it from reacting with oxygen in the air. Its high reactivity makes it useful in military applications, like incendiary devices.
- **Red phosphorus**: Features a polymeric structure, making it more stable. Unlike its white counterpart, red phosphorus is non-toxic and less flammable, which is why it's used in safety matches and fireworks. Its stability is due to its amorphous, less reactive nature compared to white phosphorus.

Chemical Properties

Chemical properties define how a substance interacts with other chemicals. These are crucial when considering allotropes of nonmetallic elements because different allotropes can display vastly different chemical behaviors.

- **Reactivity**: White phosphorus is more reactive than red phosphorus due to its molecular structure, while diamonds are less reactive than graphite because of their stable carbon network.
- **Conductivity**: Graphite conducts electricity thanks to delocalized electrons within its structure, while diamond does not.
- **Bonds**: The type and strength of atomic bonds in allotropes determine properties like hardness and reactivity.

• Diamond's covalent tetrahedral bonds contribute to its hardness.
• Graphite's planar bonds allow for electrical conductivity.
• Fullerenes' molecular bonds enable unique applications in technology.

Understanding these properties is essential in applying and utilizing nonmetallic allotropes in various industrial, scientific, and technological fields.