Carbon Lattices and Nanomaterials Key Learning Objectives the

Carbon Lattices and Nanomaterials Key Learning Objectives • the structure and bonding of diamond and graphite that explain their properties (including heat and electrical conductivity and hardness) and their suitability for diverse applications • the structures, properties and applications of carbon nanomaterials including graphene and fullerenes.

• the structure and bonding of diamond and graphite that explain their properties (including heat and electrical conductivity and hardness) and their suitability for diverse applications The Two Different Types Of Covalent Compounds Covalent compounds can be formed when non-metals are chemically combined. Each atom shares its electrons with others. The electrostatic attraction between a shared pair of electrons and the positively charged nuclei is called a covalent bond. Covalent substances can be separated into two major groups: 1. Covalent molecular substances – consist of a small number of atoms to form small molecules such as carbon dioxide (CO 2) 2. Covalent lattices – consist of an infinite number of atoms to form giant network lattices (diamond) and layer lattices (graphite).

What are the allotropes of carbon? Diamond and graphite appear to be very different substances but what do they have in common? Both diamond and graphite are made up of carbon atoms. Different forms of the same element are called allotropes. These allotropes of carbon have different properties because the atoms are bonded in different arrangements which create different giant structures. Allotrope-Structural modifications of the same element. Vary in physical and chemical properties.

What are giant covalent structures? In some substances, such as sand, diamond and graphite, millions of atoms are joined together by covalent bonds. The covalent bonds in these substances do not form molecules but vast networks of atoms called giant covalent structures. All the bonds are covalent, so giant covalent structures have very high melting and boiling points, and are usually hard. graphite (C), diamond (C), graphene (C) and quartz (Si. O 2)

How does structure affect properties? How do the different structures of diamond and graphite influence their properties?

What is the structure of graphite?

Graphite • Graphite is a covalent layer lattice. • Each layer is connected by weak intermolecular forces known as London Forces are shown as the delocalised electrons move around in the sheet, very large temporary dipoles can be set up which will induce opposite dipoles in the sheets above and below - and so on throughout the whole graphite crystal. • Layers consist of hexagonal rings. • Each carbon atom adopts a trigonal planar geometry (bond angles 120*) and is strongly covalently bonded to 3 other carbon atoms. • That leaves a fourth electron in the bonding level. These electrons in each carbon atom become delocalised over the whole of the sheet of atoms in one layer and are free to wander throughout the whole sheet. • There is, however, no direct contact between the delocalised electrons in one sheet and those in the neighbouring sheets. • The atoms within a sheet are held together by strong covalent bonds.

the structure and bonding of diamond and graphite that explain their properties (including heat and electrical conductivity and hardness) and their suitability for diverse applications. The Physical Properties Of Graphite • Has a high melting point, similar to that of diamond. In order to melt graphite, it isn't enough to loosen one sheet from another. You have to break the covalent bonding throughout the whole structure. • Has a soft, slippery feel, and is used in pencils and as a dry lubricant for things like locks. You can think of graphite rather like a pack of cards. • Has a lower density than diamond. This is because of the relatively large amount of space that is "wasted" between the sheets. • Is insoluble in water and organic solvents - for the same reason that diamond is insoluble. Attractions between solvent molecules and carbon atoms will never be strong enough to overcome the strong covalent bonds in graphite. • Conducts electricity. The delocalised electrons are free to move throughout the sheets. If a piece of graphite is connected into a circuit, electrons can fall off one end of the sheet and be replaced with new ones at the other end.

What is the structure of diamond?

Diamond • Each carbon shares electrons with four other carbon atoms - forming four single bonds in a tetrahedral arrangement (bond angle 109. 5*) • This is a giant covalent structure - it continues on and on in three dimensions.

The Physical Properties Of Diamond • Has a very high melting point (almost 4000°C). Very strong carbon-carbon covalent bonds have to be broken throughout the structure before melting occurs. • Is very hard. This is again due to the need to break very strong covalent bonds operating in 3 -dimensions. • Doesn't conduct electricity. All the electrons are held tightly between the atoms, and aren't free to move. • Is insoluble in water and organic solvents. There are no possible attractions which could occur between solvent molecules and carbon atoms which could outweigh the attractions between the covalently bound carbon atoms.

Graphene- Another Allotrope of Carbon • Consists of a single planar sheet of carbon atoms arranged hexagonally. • Is only one atom thick. • Each carbon atom is covalently bonded to 3 other carbon atoms. • Came from pulled apart graphite.

Are there other allotropes of carbon? A third class of carbon compounds have been discovered in recent years. These are called fullerenes. Buckminsterfullerene is one type of fullerene. It contains 60 carbon atoms, each of which is bonded to three others by two single bonds and one double bond. C C The atoms in this allotrope of carbon form a sphere, like the shape of a football. The molecules can be called ‘bucky balls’. They are large but are not classified as giant structures.

Fullerene- C 60 or Bucky balls • If Graphene gets rolled up it forms a carbon nano tube which if rolled up into a sphere becomes fullerenes. • In the polyhedron cage there are 20 hexagonal surfaces and 12 pentagonal surfaces and each carbon is covalently bonded to three others. • Not a covalent network solid, made of molecules with strong covalent bonds but with weak Van Der Waals/Dispersion forces between the molecules

What is the structure of sand? Sand is mostly made of the mineral quartz, which is silicon dioxide. It has a giant covalent structure made up of silicon and oxygen atoms. Each silicon atom (2. 8. 4) is bonded to four oxygen atoms, and each oxygen atom (2. 6) is bonded to two silicon atoms. O Si O O O