Three main factors are important when determining the properties of a substance:
The types of elementary particles contained. The substance can contain atoms, ions or molecules. For example, if it contains ions (such as sodium chloride), it will conduct
electricity when melted or dissolved in water. in order to be soluble in water, the substance must contain lons or polar molecules.
Particles may have ionic, covalent, metallic, or weak intermolecular forces. The stronger the bond, the higher the melting/boiling point and hardness of the substance.
For example, silicon dioxide (SIO,) has strong covalent bonds, connecting each atom to several other atoms to form a giant covalent structure. The atoms in silica are difficult to separate, making it very hard and difficult to melt.
On the other hand carbon dioxide has strong covalent bonds between the C and O atoms. But these molecules have weak intermolecular forces between them. The molecules are therefore easily separated and so CO, has a low melting/boiling point.
Particles may be arranged in planes (for example, polymers), in layers (for example, clays, graphite) or in a variety of three-dimensional networks. In graphite atoms are arranged in 2-dimensional layers. This allows the layers of graphite to move over one another (for example, graphite pencil writing). Diamonds have a large three-dimensional network of carbon atoms, which make it the hardest substance on earth. Metals also have giant structures. metallic bonding is stong, most metals have very high melting and boiling points and are thermally stable.
Electrical conductivity is achieved by the movement of charged particles.lonic compounds cannot conduct electricity in the solid state because their ions remain in a fixed position and cannot move. When an ionic compound is melted or dissolved in water. It is ionized, its ions move freely in molten or aqueous solution. Therefore electricity can pass through a molten ionic compound or its aqueous solution.
Covalent compounds have no free charged particles, so they do not conduct electricity. However, some covalent compounds conduct electricity when dissolved in water. For instance, acids like HCI, H,SO,, HNO, etc. When these acids are dissolved in water, they ionize and form high concentrations of H' ions and negatively charged ions. These ions can move freely in aqueous solution. Therefore, aqueous solutions of acids conduct electricity.
Metals are good conductor of electricity because they have free electrons. These electrons are not associated with a single atom. These electrons begin to flow under the influence of electricity. Therefore metals allow electricity to pass through.
Compounds that consists of covalent molecules are called covalent compounds. The Intermolecular forces between their molecules are much weaker than the covalent bonds. Therefore, covalent compounds have low metting and boiling points. Since their molecules do not contain any free electrons or lons, they are poor conductors of electricity
Tables shows melting and boiling points of some common covalent and ionic compounds.
| Compound | Melting Point (°C) | Boiling Point (°C) |
|---|---|---|
| Water (H₂O) | 0 | 100 |
| Methane (CH₄) | -183 | -162 |
| Ethanol (CH₃CH₂OH) | -117 | 78 |
| Compound | Melting Point (°C) | Boiling Point (°C) |
|---|---|---|
| Sodium Chloride (NaCl) | 801 | 1465 |
| Sodium Fluoride (NaF) | 996 | 1695 |
| Magnesium Chloride (MgCl₂) | 714 | 1412 |
Covalent compounds usually have much lower melting points than ionic compounds. For example, a common covalent compound of water has a melting point of 0°C and a boiling point of 100°C. The melting points and boiling points of the common ionic compound sodium chloride are 801°C and 1465°C.
This is because ionic compounds involve breaking the ionic bond. Breaking the electrostatic forces between ions requires large amounts of energy. Thus, ionic compounds have high melting points and boiling points.
Melting of covalent solids involves the breaking of intermolecular forces, which are much weaker than electrostatic forces. Thus, less energy is required to break the intermolecular forces between covalent molecules.
Graphite's name is derived from the Greek word "graphein," meaning "to write." It is commonly called black lead. Graphite is an allotrope of carbon. Graphite is formed when carbon is subjected to the intense heat and pressure of the earth's crust and upper mantle.
Structure of Graphite
All these uses are a testament to the unique properties of graphite. The patterned bonding and layered structure make it suitable for such diverse applications.
Diamond is an allotrope of carbon in which the carbon atoms are arranged in a diamond cubic crystal lattice. Thanks to the presence of strong covalent bonds and a rigid tetrahedral structure, Diamond is the hardest material ever discovered.
In a diamond, the carbon atoms are arranged tetrahedrally. Each carbon atom is attached to four other carbon atoms 1.544 x 10 meter away with a C-C-C bond angle of 109.5°. It is a strong, rigid three-dimensional structure that results in an infinite network of atoms. This accounts for diamond's hardness, extraordinary strength and durability and gives diamond a higher density than graphite (3.514 grams per cubic centimeter).
The giant structure and extensive covalent bonding in diamond renders it extraordinary hardness, elasticity, high yield strength, less conductivity, and chemical inertness. Owing to these properties diamond has variety of applications like:
1. Diamonds are most commonly used in ornaments like rings, necklace, earrings, etc. in the gem industry, the value of diamonds is very high. They are used in making jewellery because of their durability and lustre property.
2. Its property of hardness is useful to drill, grind or cut materials. Hence, some blades used for cutting and drills in the industry used diamonds. They are present on the edges and tips in small sizes.
3. Diamonds are used in making medicines and beauty products. They are also used in making medical tools, like tools used in cataract surgery. Nano-diamonds have potential health benefits.
4. Diamonds produce high-quality sound because they are hard and vibrate easily at high speed. It is also used in DJ equipment and high-quality recorders.
The type of chemical bonds significantly influences the properties and uses of materials.