Covalent Bonding

• A covalent bond is formed between atoms by the sharing of a pair of electrons.
• Covalent bonding occurs in most non-metallic elements and in compounds of nonmetals.
• When atoms share pairs of electrons, they form covalent bonds.
• The bonds between atoms are strong.
• Strong bonds between atoms that are covalently bonded are the result of electrostatic attraction between the positive nuclei of the atoms and the pairs of negative electrons that are shared between them.
• The properties of carbon nanotubes make them useful for nanotechnology, electronics and materials.
• Carbon nanotubes are cylindrical fullerenes with very high length to diameter ratios.
• The first fullerene to be discovered was Buckminsterfullerene (C60), which has a spherical shape.
• Covalent compounds do not usually conduct electricity, exceptions include graphite and graphene.
• Fullerenes are based on hexagonal rings of carbon atoms, but they may also contain rings with five or seven carbon atoms.
• Molecules of carbon atoms with hollow shapes are known as fullerenes.
• Substances with a simple molecular structure are usually gases or liquids, or solids with low melting and boiling points.
• Substances that consist of small molecules are usually gases or liquids that have low boiling and melting points.
• All of the atoms in these structures are linked to other atoms by strong covalent bonds.
• Diamond is a solid with very high melting point and does not conduct electricity.
• In graphite, each carbon is covalently bonded to 3 other carbons, forming layers of hexagonal rings, which have no covalent bonds between the layers.
• Molecules with greater relative molecular masses have higher melting and boiling points.
• Graphene is a single layer of graphite and has properties that make it useful in electronics and composites.
• Carbon can also form fullerenes with different numbers of carbon atoms.
• These bonds must be overcome to melt or boil these substances.
• Substances with giant covalent structures are solids with high melting and boiling points.
• Graphite can conduct electricity, unlike Diamond.
• Graphite is soft and slippery.
• The layers in graphite can slide over each other due to no covalent bonds between the layers, but weak intermolecular forces.
• One electron from each carbon atom in graphite is delocalised, making graphite similar to metals, because of its delocalised electrons.
• Substances that consist of small molecules have weak intermolecular forces between the molecules, which are broken in boiling or melting, not the covalent bonds.
• Substances that consist of small molecules don’t conduct electricity, because small molecules do not have an overall electric charge.
• The melting and boiling points of substances with simple molecular structures increase, in general, with increasing relative molecular mass.
• The intermolecular forces increase with the size of the molecules, so larger molecules have higher melting and boiling points.