Most solid objects we encounter in our daily lives are opaque or translucent. Many solid materials, such as stone or wood, do not transmit light to the other side and we cannot see what is behind them. Most liquids are transparent.
Glass is an unusual example among solid materials. With its transparent structure, it can pass light and allows us to see what is inside and behind it. Therefore, glassware is an integral part of our daily life. Have you ever wondered how something as solid and durable as glass can transmit light?
Wasn’t glass made of earth? How can glass be transparent when soil is not?
Glass is made from sulfur dioxide found in the soil. Therefore, the soil is first subjected to various processes or mixed with some chemicals in order to obtain this material. Glass is formed after the raw material is exposed to high temperatures.
It all starts in the Earth’s crust. Here, the two most common elements, silicon and oxygen, react with each other to form silicon dioxide.
As it transforms into silicon dioxide, these molecules arrange themselves to form a neat crystal called quartz. Most of the particles found in sand are actually quartz.
But when you look at the sand, you don’t see anything transparent. Because the hard shaped particles and small distortions in the structure of these quartz crystals both reflect and emit the striking light. That is, they can show opaque properties.
When silicon dioxide is heated to high temperatures, it turns into a solid material, similar to the mixed structure of a liquid, in which molecules can fill any gap, just like liquids.
When quartz is heated to high temperatures, it vibrates until the bonds holding the energy molecules together are broken, thus turning into a flowing liquid. Silicon dioxide, once liquid, does not turn into a crystal again. As the molecules lose energy, they lose their ability to move regularly, that is, in solid form, and turn into a form called an amorphous solid, even as it cools.
Thus, it makes the surface of the glass uniform at a microscopic level and allows the light to hit it without spreading it in different directions. But this is not enough to explain why light is not absorbed as in many solids, but can instead pass through glass.
To understand why glass is transparent, we need to look down to the subatomic level.
The atom has a nucleus around which electrons are circulated. However, most of this part consists of spaces. In fact, if an atom were the size of a stadium, its core in the middle would be almost the size of a pea, and the electrons would be like grains of sand far away. This leaves enough space for the light to pass through without hitting those particles.
If every atom is filled with so much space, the real question we should ask is “Why is glass transparent?” not, “Why aren’t all materials transparent?” should be.
To answer this question, we need to look at the different energy levels that electrons can have. Let’s think of these as the rows of seats in the stadium. An electron is given a row to sit first, but can move to a better rank if it reaches a certain energy.
The ticket to a better lineup is to absorb one of these photons of light. Thus, the electron reaches the energy it needs. However, this photon must provide the electron with exactly the required amount of energy. Otherwise, the photon will just pass by.
Photons in ultraviolet light give exactly the desired amount of energy and are absorbed, so if you want to tan, you cannot sunbathe behind glass.
This magnificent property of being both solid and transparent has enabled glass to be used in different ways for centuries. Through our windows that keep the harsh conditions of nature outside and let the light in; down to the lenses that allow us to see planets and very small living things in the depths of the universe.
This is exactly why it is almost impossible to imagine modern life without glass.
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