Covalent Structures Flashcards
What is a lattice?
A lattice is a regular repeated 3. Dimensional arrangement of atoms, ions or molecules in a metal or other crystalline solid.
Why is diamond not a molecule?
It is not a molecule, because the number of atoms joined up in a real diamond is completely variable depending on the size of the lattice.
Properties of diamond? (3)
Properties:
● 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
atoms, and aren’t free to move.
Explain why graphite is special?
Graphite has a layer structure. Each carbon atom uses three of its electrons to form simple bonds to its three close neighbours. That leaves a fourth electron in the bonding level. These “spare” electrons in each carbon atom become delocalised over the whole of the sheet of atoms in one layer. They are no longer associated directly with any particular atom or pair of atoms, but are free to wander throughout the whole sheet.The important thing is that the delocalised electrons are free to move anywhere within the sheet - each electron is no longer fixed to a particular carbon atom. There is, however, no direct contact between the delocalised electrons in one sheet and those in the neighbouring sheets.
Why are metals good conductors of electricity?
Metallic Lattices
Metallic crystals consist of metal cations (positive kernals) surrounded by a “sea”
of delocalized electrons (see figure below). These electrons do not belong to any
one atom, but are capable of moving through the entire crystal. As a result,
metals are good conductors of electricity.
