Chemical Bonding and Structure

Ionic Bonding

Bonding between a non-metal and a metal where electrons are transferred from the metal to the non-metal. This results in the non-metal forming a negative ion and the metal forming a positive ion. The structure is a giant ionic lattice with strong electrostatic forces between ions. A lot of energy is needed to break these forces, resulting in high melting and boiling points. Ionic compounds conduct electricity when aqueous or molten, as the ions are free to move around. They can be represented using dot and cross diagrams.

Covalent Bonding

Bonding between two non-metals. Covalent compounds do not conduct electricity as there are no charged particles. Small molecules are liquids or gases at room temperature due to weak intermolecular forces. However, the intermolecular forces get stronger the bigger the molecule is. This results in low melting and boiling points. Covalent bonds involve the sharing of electrons between atoms, resulting in strong electrostatic forces. Giant covalent structures are solid at room temperature, have very high melting points, and have strong covalent bonds between atoms. These bonds must be broken to melt the solid. Examples include diamond and silicon dioxide. Polymers are repeating units of covalent bonds that have strong intermolecular forces and are solids at room temperature. Covalent bonds can be represented using dot and cross (Venn diagram) diagrams.

Metallic Bonding

Bonding between two metals. Metallic bonding involves positive metal ions in a sea of delocalized electrons, arranged in regular layers. Metals are malleable as the layers can slide over each other, which means pure metals are often very soft. There are strong electrostatic forces between the delocalized electrons and positive ions. Due to the delocalized electrons, metals conduct electricity when in a liquid state.

Alloys

Alloys are mixtures of metals. The distortion and randomness of layers in alloys make them much harder and less malleable than pure metals. Examples include steel.

Particle Theory

• An increase in concentration results in an increase in pressure.
• An increase in volume results in a decrease in pressure.
• An increase in temperature results in an increase in pressure.

Allotropes of Carbon

Diamond

Diamond has a giant covalent structure with four covalent bonds per carbon atom. They have a rigid structure and are very hard. Diamond does not conduct electricity because there are no charged particles. It has a very high melting point due to the strong covalent bonds.

Graphite

Graphite has a giant covalent structure and a high melting point due to strong covalent bonds. Each carbon atom forms three covalent bonds, with the fourth electron being delocalized. This delocalized electron allows graphite to conduct electricity. Graphite consists of layers of hexagonal rings. Due to the lack of bonds between the layers, they can slide over each other, making graphite soft and slippery.

Graphene

Graphene is a single, one-atom-thick layer of graphite. It is very strong and very light. Graphene conducts electricity due to its delocalized electrons. It is used to make composites.

Fullerenes

Fullerenes are hollow shapes with carbon atoms arranged into hexagonal rings. Buckminsterfullerene (buckyballs) are hollow spheres. They are used to deliver drugs to the body and are good catalysts. Nanotubes are tubes of fullerenes used in electronics and composites. They have a high length-to-diameter ratio.

Nanoparticles

Nanoparticles are a few hundred atoms in size, ranging from 1 to 100 nm. Fine particles have diameters between 1 x 10^-7 and 2.5 x 10^-6 m. Coarse particles, such as dust, have diameters between 1 x 10^-5 and 2.5 x 10^-6 m. Nanoparticles have a large surface area to volume ratio.

Uses of Nanoparticles

• Electric circuits
• Catalysts
• Suncream
• Deodorants and wound dressings (silver nanoparticles have antibacterial properties)

Nanomedicine is a relatively new field, so there could be potential long-term risks that we are unaware of.