Bonding & Structure: Covalent Bonding
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What is a covalent bond?
A shared pair of electrons between two atoms.
What properties do simple molecular covalent substances have?
• do not conduct electricity • low melting and boiling points
What is a simple covalent molecule in terms of its structure?
• contain only a few molecules (<100 atoms) • held together by covalent bonds
Why do simple covalent molecules not conduct electricity?
They do not have any free electrons or ions.
Why do simple covalent molecules have low melting and boiling points?
Little energy is needed to overcome the weak intermolecular forces
What is strong in a simple covalent molecule, what is weak?
• strong covalent bonds between atoms • weak intermolecular forces between molecules
How do intermolecular forces change as the mass/size of the molecule increases?
They increase
What do stronger intermolecular forces mean for a substance‘s melting and boiling points?
• increases melting and boiling points • more energy needed to overcome these forces
What are giant covalent substances?
Atoms covalently bonded in a giant lattice (regular repeated structure)
What properties do giant covalent substances have?
• high melting and boiling points • most dont conduct electricity (dont normally have delocalised e-
Why do giant covalent substances have high melting and boiling points?
They have strong covalent bonds which require a lot of energy to overcome.
What are some allotropes of carbon?
• diamond • graphite • fullerenes • nanotubes • graphene
What is an allotrope?
Different forms of an element that are bonded differently
Describe the structure of diamond.
• each carbon atom is joined to 4 other carbon atoms by strong covalent bonds • the carbon atoms form a regular tetrahedral structure • no delocalised electrons
Why is diamond very hard?
It has strong covalent bonds.
Why does diamond have a very high melting and boiling point?
It has strong covalent bonds.
Why is diamond not a conductor of electricity?
It has no delocalised electrons - all are involved in bonding
What properties does diamond have?
• very hard • very high melting point • not a conductor of electricity
Describe the structure of graphite.
• 3 covalent bonds per carbon atom • layers of hexagonal rings • weak forces of attraction between layers
What properties does graphite have?
• slippery, makes a good lubricant • conductor of electricity • softer than diamond
Why is graphite slippery?
Layers can slide due to weak intermolecular forces
Why is graphite soft?
The intermolecular forces of attraction between layers are weak
Why can graphite conduct electricity?
Only bonded to 3 other carbons so one delocalised electron per carbon atom which can carry a charge through the structure.
Describe the structure and properties of silicon dioxide.
• SiO2: made up of silicon and oxygen • has the same structure and properties as diamond