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# What is a Solid?

You have probably heard the word “solid” more than once, but you may not know what it means. Solids are objects that do not disappear into air, have a fixed shape, and resist forces that are applied perpendicular to their surface. You may have even heard the term “solid chocolate” before, which is chocolate that is spread evenly throughout. If you’re unfamiliar with the term, here are some explanations to help you understand what solids are and what they do.

## Solids are arranged in a lattice

Most solids are crystalline in structure, though not all materials are crystalline. Solids are formed when their atoms form an ordered three-dimensional pattern. Such an arrangement is referred to as a lattice. It is also possible for a solid to aggregate in no particular order and are referred to as amorphous solids. The name amorphous is derived from the Greek word for “shapeless.”

## They resist forces applied perpendicular or parallel to a surface

A solid is a substance that is hard enough to resist pressure applied to its surface. Its surface area, called A, determines the amount of pressure it can withstand. Solids can resist pressure from different directions up to a certain limit. A solid retains its clean shape even under pressure. A fluid, on the other hand, takes on the shape of its container. As a result, the force applied to it will tend to flow from the surface.

## They have a fixed shape

When you hold a solid, its particles are closely packed together and can’t move at all. Unlike liquids, which spread out to fill a container, solids hold their shape no matter how much you push or pull them. Matter is the stuff of the universe and comprises atoms, molecules, and ions. Solids are different from liquids because their particles are free to move around within their substance, but liquids can change shape and volume.

## They are dense

The adjective dense means opaque, allowing little light to pass through. Dense sets approximate space well. The word dense is also a synonym of the adjectives densely and denser. Both of these words derive from the Latin word densus, meaning “thick”.

## They conduct electricity

There are two types of solids – metallic and ionic. While ionic solids do not conduct electricity, metals can. They do, however, have metallic bonds which hold the copper sample together. These bonds are caused by motions of many free electrons, which can conduct electricity when they move. Hence, the name “metal” for solids that conduct electricity. But what are metallic and ionic solids?

## They are a good conductor of heat

Among all liquids, mercury is the best conductor of heat. Mercury is also known as liquid silver and is used in thermometers. In addition, silver and copper are good conductors of electricity and heat. Alcohols, on the other hand, do not conduct heat as they do not contain ions, which means that they do not conduct electricity. However, this does not mean that alcohols are bad conductors of heat.

## They are a good conductor of electricity

Whether a solid is a good conductor of electricity is based on its size. While copper, aluminium, and silver are the best conductors, a solid can also be an insulator or a good conductor depending on the type of material. The list below includes pure elements, alloys, and their corresponding sizes. Because of quantum mechanical effects, conductivity depends on size.