TYPES OF CRYSTALS: Flashcards
What are crystal types?
= regular arrangement of ions or atoms
= most solid elements/compounds exist on crystals
What are macromolecular crystals? (giant covalent lattices)
= regular arrangement of atoms held together by covalent bonds (non-metals reacting with a non-metal).
= E.g: Diamond, Graphite + Silicom
What is the structure of diamond?
= each carbon atom is bonded to 4 carbon atoms
= tetrahedral
= 109 degrees around each carbon bond
=
What is the structure of graphite?
= each carbon bonded to 3 carbons
= 1 spare electron per atom- delocalised can move between the layers
= hexagon shapes in layers
= weak van der waalls forces between the layers
Why is graphite soft?
= the layers can slide
Why can graphite conduct electricity?
= delocalised electrons can carry the charge
Why does macromolecules have high melting and boiling points?
= difficult to overcome the covalent bonds
What structure is silicon?
= tetrahedral
= silicon bonded to 4 oxygen
= oxygen bonded to 2 silicon
What are metallic crystals?
= ions that are closley packed together in an regular arrangement
What are the different types of packing for metallic crystals?
= body centered cubic
= face centered cubic
= hexagonal close packing
Whats an example of a body centered cuboic metallic crystal and what is the coordination number?
= Iron
= CN: 8
Whats an example of a face centered cuboic metallic crystal and what is the coordination number?
= copper
= CN: 12
Whats an example of a hexagonal close packing metallic crystal and what is the coordination number?
=magenesium
= CN: 12
What are molecular crystals?
= covalent bonded molecules held by weak intermolecular forces
Why do molecular crystals have a low melting points?
= intermolecular forces are broken easily
