What is glass?
Glass is a manufactured substance made mainly by melting silica (silicon dioxide, SiO2), usually from sand, at a very high temperature. It is hard, transparent, an electrical insulator, resistant to chemicals and does not react with most substances, which is why it is used for windows and containers.
Types of glass
Different additives give glass different properties for different uses:
| Type | Main components | Use |
| Fused silica glass | SiO2 only | Lenses, high-temperature apparatus |
| Soda-lime glass | SiO2, Na2O, CaO | Windows, bottles |
| Borosilicate glass | SiO2, B2O3 | Cookware, laboratory glassware |
| Lead crystal glass | SiO2, PbO | Decorative items, prisms |
Key idea
Soda-lime glass is the most common and cheapest, used for windows and bottles. Borosilicate glass contains boron oxide (B2O3), giving it a low expansion so it resists sudden temperature change (thermal shock) — ideal for cookware and laboratory apparatus.
Properties and uses
Adding lead(II) oxide (PbO) raises the density and refractive index, so lead crystal glass sparkles and is used for decorative cut glass. Fused silica withstands very high temperatures and transmits ultraviolet light. Choosing the right glass means matching its properties to the job.
Worked example
Which glass is best for a beaker heated with a Bunsen burner? Borosilicate glass. Because its low thermal expansion lets it resist thermal shock, it will not crack when heated or cooled quickly, unlike ordinary soda-lime glass.
Remember
- Silica (SiO2) from sand is the main raw material of all glass.
- Soda-lime = cheap, everyday windows and bottles.
- Borosilicate = heat-resistant cookware and lab glass.
- Lead crystal = dense, sparkling decorative glass.