Explain why substances with giant covalent structures are solids with high melting and boiling points ?

Answer:

Explanation:

Substances with giant covalent structures are solids with high melting and boiling points due to the nature of the covalent bonds and the three-dimensional network they form within the crystal lattice. This structure is also often referred to as a network covalent structure. Let's break down the key reasons why these substances have such properties:

1. **Strong Covalent Bonds**: In giant covalent structures, each atom forms strong covalent bonds with neighboring atoms. Covalent bonds involve the sharing of electrons between atoms. This sharing results in the formation of very strong and directional bonds, which require a significant amount of energy to break.

2. **Three-Dimensional Network**: In these substances, the covalent bonds extend in a three-dimensional network throughout the entire structure. This means that every atom is bonded to several neighboring atoms in all three spatial dimensions. This extensive network of covalent bonds creates a robust and interconnected structure.

3. **Lack of Weak Intermolecular Forces**: Unlike some other types of solids (e.g., molecular solids or ionic solids), giant covalent structures lack weak intermolecular forces, such as Van der Waals forces. In molecular solids, weak intermolecular forces are responsible for their relatively low melting and boiling points. In giant covalent structures, the primary forces holding the atoms together are the covalent bonds themselves, which are much stronger.

4. **High Bond Energy**: The covalent bonds in giant covalent structures have high bond energies, meaning that a substantial amount of energy is required to break these bonds. When a solid is heated, the energy provided must be sufficient to overcome the covalent bonds' strength, leading to the high melting and boiling points.

5. **Rigidity and Structural Integrity**: The three-dimensional covalent network imparts rigidity and structural integrity to the substance. This network resists deformation and allows the substance to maintain its solid form at high temperatures, as the covalent bonds continuously hold the structure together.

Examples of substances with giant covalent structures include diamond (composed of carbon atoms), graphite (also composed of carbon atoms but arranged differently), and various forms of silica (e.g., quartz and silicon dioxide). Diamond, in particular, is known for its exceptional hardness, high melting point, and remarkable optical properties, all of which are attributed to its giant covalent structure.

In summary, giant covalent structures have high melting and boiling points because of the strong covalent bonds, the three-dimensional network of bonds, and the absence of weak intermolecular forces. These factors combine to create a solid with exceptional stability and resistance to temperature-induced phase changes.

Final answer:

Substances with giant covalent structures have high melting and boiling points due to the strong covalent bonds that exist throughout their structure. The size of the molecules and the polarizability of the atoms also impact these properties. However, covalent compounds generally have lower melting and boiling points than ionic compounds.

Explanation:

Substances with giant covalent structures are typically solids with high melting and boiling points due to the extensive network of strong covalent bonds that require a lot of energy to break. An example of this would be carbon dioxide (CO₂) and iodine (I₂) which are molecular solids with defined melting points. The size of the molecule impacts the strength of the intermolecular attractions.

Larger atoms have valence electrons that are further from the nucleus and less tightly held, making them more easily distorted to form temporary dipoles leading to stronger dispersion forces. This concept is known as polarizability. Therefore, substances which consist of larger, nonpolar molecules tend to have higher melting and boiling points due to larger attractive forces.

However, compounds with covalent bonds have different physical properties than ionic compounds. Covalent compounds generally have much lower melting and boiling points than ionic compounds, due to the weaker attraction between electrically neutral molecules than that between electrically charged ions.

Learn more about Giant Covalent Structures here:

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