3.2 nature of covalent and dative covalent bonds Flashcards
What is a covalent bond?
A covalent bond is a shared pair of electrons between two non-metals.
What is a dative covalent bond?
A dative covalent bond is when both of the electrons in the shared pair are from a single atom.
Example of a dative covalent bond.
Ammonia (NH3) has a lone electron pair that can form a dative bond with a H+ ions to produce an ammonium ion (NH4+).
When a dative bond has formed it is treated as a standard covalent bond.
It reacts in exactly the same way as covalent bonds and does not differ in strength.
What is a simple molecular structure?
Substances with a simple molecular structure consist of covalently bonded molecules held together with weak van der waals forces. These are a type of intermolecular force that act between the molecules holding them in a structure.
What are the properties of substances with simple molecular structures?
- Low melting and boiling points
- Insoluble (some exceptions)
- Cannot conduct electricity when solid or molten
Why do they have low melting and boiling points?
The van der waals forces between molecules, holding them together, are weak so therefore not a lot of energy is required to overcome the forces.
Why are they not soluble?
The molecules are generally non-polar meaning that they cannot interact with water, and therefore cannot be dissolved.
Why can’t they conduct electricity?
Simple molecular substances cannot conduct electricity as their structure contains no charged particles.
What is a macromolecular structure?
Substances that have a macromolecular structure are covalently bonded into a giant lattice structure, with each atom having multiple covalent bonds.
What are the properties of substances with a macromolecular structure?
- High melting and boiling points
- Insoluble
- Conductive when solid (graphite)
- Not conductive when solid (diamond, sand)
Why do they have high melting and boiling points?
There are many strong covalent bonds in macromolecular structures which require a lot of energy to break.
Why is graphite conductive when solid?
There are delocalised electrons between layers, meaning these electrons can carry a flow of charge and conduct electricity.
