1. Covalent Properties Main Concept:
Covalent network solids have properties that reflect their underlying 2-D or 3-D networks of covalent bonds. Covalent network solids generally have extremely high melting points and are hard.

2. Covalent Properties Properties of Covalent Networks Structure
Melting Points
Other Properties
Examples
Graphite
Silicon

3. - Covalent network solids consist of atoms covalently bonded into two-dimensional or three-dimensional networks

4. Covalent network solids are only formed from nonmetals:
- elemental (diamond or graphite)
- two nonmetals (silicon dioxide and silicon
carbide)
- properties of covalent network solids reflect their structure
- have high melting points because all atoms are covalently bonded

5. graphite diamond silica
- Three-dimensional covalent networks tend to be rigid and hard because covalent bond angles are fixed
- Generally, covalent network solids form in carbon group because of ability to form four covalent bonds

6. Graphite:
- an allotrope of carbon that forms sheets of two-dimensional networks
- has high melting point because covalent bonds between the carbon atoms making up each layer are relatively strong
- is soft because the adjacent layers can slide past each other relatively easily; major forces of attraction between layers  London dispersion forces

7. Silicon
- A covalent network solid and semiconductor
- forms a three-dimensional network similar in geometry to a diamond
- conductivity increases as temperature increases
- Periodicity can be used to understand why doping with an element with one extra valence electron converts silicon into an n-type semiconducting (negative charge carrying) material
- basis of modern electronics are junctions between n-doped and p-doped materials used to control electrons flow.