What are the 2 types of structures formed by covalently bonded substances?
Simple molecular
Giant covalent lattice structures
What state are most small molecules in at room temperature?
Liquids or gases
What are 2 examples of molecular solids?
Iodine
Ice
Describe the structure of iodine (3 things)
Diatomic molecule held together by weak intermolecular forces, as solid molecules held in regular lattice
What are 5 examples of giant covalent lattices?
Diamond
Graphite
Graphene
Silicon
Silicon dioxide
What are allotropes?
Two or more forms of same element in which atoms or molecules are arranged in different ways
What are 4 allotropes of carbon?
Diamond
Graphene
Graphite
C60
What are 4 physical properties of diamond and silicon dioxide?
high melting point
Very hard
Doesn’t conduct electricity
Insoluble in water and organic solvents
Why are the bonds in diamond so strong?
Bonding electrons localised close to nucleus
Why do both diamond and silicon dioxide not conduct electricity?
All electrons held tightly between atoms and aren’t free to move
Why is diamond very hard?
Rigid 3D tetrahedral arrangement of atoms held together by strong covalent bonds
Why are both diamond and silicon dioxide insoluble in water and organic solvents?
No possible attractions between solvent molecules and carbon atoms that could outweigh attractions between covalently bonded carbon atoms
Why do diamond, silicon and silicon dioxide all have similar physical properties?
Identical structures - all form giant covalent structure with a tetrahedral arrangement of atoms
Why does graphite have delocalised electrons?
Each carbon atom only forms 3 bonds so each carbon atom has a valence electron free which is not localised
Why is graphene a giant covalent lattice and C60 a molecular solid?
C60 has fixed number of atoms in molecule whereas graphene has variable number of atoms determined by size of crystal
In which direction can graphite conduct and why?
Only along sheets, electrons are only moving along sheets, individual sheets too far apart
