Glass

Definition and Composition

Glass is an amorphous solid, meaning it does not have a regular, repeating crystal structure like many other solids. Instead, its atoms are arranged randomly. This means glass lacks the long-range order seen in crystalline solids, which have atoms arranged in a repeating lattice.

The main component of most glass is silicon dioxide (SiO8), commonly found in sand. To improve its properties, other metal oxides such as sodium oxide and calcium oxide are added during manufacture.

These additives change the melting point, durability, and chemical resistance of the glass, making it suitable for different uses.

Properties of Glass

• Hard and brittle: Glass is hard, so it resists scratches, but it is brittle and breaks easily when struck.
• Transparent: It allows light to pass through, which is why it is used for windows and lenses.
• Non-crystalline structure: Unlike crystalline solids, glass has no long-range order in its atomic arrangement.
• Does not conduct electricity: Glass is an electrical insulator because it has no free electrons or ions to carry charge.

For example, glass windows let sunlight into a room while keeping out the weather, and glass bottles protect liquids without conducting electricity or heat.

Types of Glass

Soda-lime glass is the most common type, made by adding sodium oxide (from soda ash) and calcium oxide (from limestone) to silicon dioxide. It is cheap and used for windows, bottles, and jars.

Borosilicate glass contains boron oxide, which makes it more heat resistant. This type is used for laboratory glassware and kitchenware like Pyrex because it can withstand rapid temperature changes without cracking.

Tempered glass is strengthened by heating and then rapidly cooling it. This process makes it much tougher and safer because if it breaks, it shatters into small, less dangerous pieces. It is used in car windows and smartphone screens.

Uses of Glass

• Windows and bottles: Soda-lime glass is widely used for making windows and containers because it is transparent, cheap, and easy to shape.
• Laboratory equipment: Borosilicate glass is ideal for lab equipment such as beakers and test tubes because it resists heat and chemical attack.
• Optical fibres: Special types of glass are used to make optical fibres, which transmit data as light signals over long distances with very little loss. This technology is essential for high-speed internet and telecommunications.

For instance, optical fibres are made from very pure glass that allows light to travel through bends without escaping, enabling fast communication networks.

Learning Example: Calculating the percentage of silicon dioxide in soda-lime glass

If soda-lime glass contains 70% silicon dioxide, 15% sodium oxide, and 15% calcium oxide by mass, what mass of silicon dioxide is in a 200 g piece of soda-lime glass?

Calculate the mass of silicon dioxide:

$\text{Mass of SiO}_2 = 70\% \times 200\, \text{g} = \frac{70}{100} \times 200 = 140\, \text{g}$

So, there are 140 g of silicon dioxide in the 200 g piece of soda-lime glass.