- Electrostatic force of attraction between shared pair of electrons and the nuclei on either side
- Non-metal atoms involved
- Covalent bonding: Non-metal atoms share one or more pairs of electrons by overlapping valence shells to give each a nobel gas structure
- A covalent bond is a shared pair of electrons
- There is a force of attraction between the bonding pair of electrons and the nuclei of the atoms at each side
- Hydrogen atoms only need 2 electrons in their outer level to reach the noble gas structure of helium
- Octet Rule: Atoms gain, lose or share eelectrons when they combine with other atoms to acquire a stable octet (8) of electrons
- There are exceptions: and
Properties
- Non-conductors of electricity
- Electrons are localised in the electron cloud or as bonding pairs
- Therefore, they are immobile, and cannot conduct charge
- Bad conductors of heat
- No free particles that can move from one end of the particle to another, carrying kinetic energy (temperature)
- Thus, it is a bad conductor of heat
- Soft
- Only weak intermolecular forces exist between the molecules and so these molecules can be easily separated and rearranged when a force is applied, making them soft
- Low melting/boiling point
- Only weak intermolecular forces exist between the molecules
- Small amount of energy is need to overcome these bonds, and there is a low melting/boiling point
- These increase with molecular size, which increases the strength of the bonds
Note: These are for Covalent Molecular Structures, not Covalent Network Structures, which you do not need to know .
Ok Ms Pilling is talking about Silicon Dioxide, Graphite, and Diamond, so here you go, I guess.
Covalent Networks (Elements)
Silicon
- Each silicon atom is covalently bonded to 4 other silicon atoms in a tetrahedral 3D shape
- Weaker than Diamond
Graphite
- An allotrope of carbon
- Where each carbon atom is bonded to 3 other carbon atoms via single bonds only in a hexagonal arrangement, in multiple 2D layers
- There exists a layer of delocalised electrons between each 2D layer of carbons
- The layers are attracted to each other due to electrostatic attraction between the delocalised electrons that exist in each layer
Diamond
- Another allotrope of carbon where each carbon atom is covalently bonded to 4 other carbon atoms in a tetrahedral 3D shape
- Has the standard properties of a covalent network solid
- Stronger than Silicon, as there is a greater ESF in between the carbons, due to a decrease in atomic radius
Covalent Networks (Compounds)
Silicon Dioxide
- In silicon dioxide, each silicon atom is covalently bonded to 4 other oxygen atoms which in turn are bonded to 2 silicon atoms
- Silicon dioxide is also known as quartz, and has the same properties as a general covalent network substances