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# Solids

## Introduction to one of the four states of matter where

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Solids

What do you think this picture shows? Could it be a delicate glass sculpture created by a talented artist? It’s delicate alright, but it’s not glass, nor was it created by an artist. It’s actually made of ice and it’s a work of nature. Now can you guess what it is? It’s a snowflake, as viewed under a microscope.

### Snowflakes and Other Solids

A snowflake is made of ice, or water in the solid state. A solid is one of four well-known states of matter. The other three states are liquid, gas, and plasma. Compared with these other states of matter, solids have particles that are much more tightly packed together. The particles are held rigidly in place by all the other particles around them so they can’t slip past one another or move apart. This gives solids a fixed shape and a fixed volume.

### Solids have low kinetic energy and high intermolecular forces.

If you pour water into a pot on the stove, how do you know the water will stay in the pot? How do you know the pot will hold the water and keep it from spilling all over?

The pot is a solid, which is something that has a definite shape and volume. The particles in a solid are held in place by strong intermolecular forces between the atoms or molecules.

Of the states of matter, solids have the least amount of kinetic energy. The molecules are moving, but not freely. They vibrate but stay in position. As solids are heated, the molecules gain more kinetic energy and start to vibrate faster.

### Types of Solids

Not all solids are alike. Some are crystalline solids; others are amorphous solids. Snowflakes are crystalline solids. Particles of crystalline solids are arranged in a regular repeating pattern, as you can see in the sketch below. The repeating particles form a geometric shape called a crystal. You can watch a snowflake crystal forming at the following URL: http://www.its.caltech.edu/~atomic/snowcrystals/movies/movies.htm. Another crystalline solid is table salt (sodium chloride). Crystals of table salt are pictured in the Figure below.

Amorphous means “shapeless.” Particles of amorphous solids are arranged more-or-less at random and do not form crystals, as you can see in the Figure below. An example of an amorphous solid is cotton candy, also shown in the Figure below.

Q: Look at the quartz rock and plastic bag pictured in the Figure below. Which type of solid do you think each of them is?

A: The quartz is a crystalline solid. Rocks are made of minerals and minerals form crystals. You can see their geometric shapes. The bag is an amorphous solid. It is made of the plastic and most plastics do not form crystals.

### Summary

• A solid is a state of matter in which particles of matter are tightly packed together. This holds the particles rigidly in place and gives solids a fixed shape and fixed volume.
• Crystalline solids have particles that are arranged in a regular repeating pattern. They form crystals. Amorphous solids have particles that are arranged more-or-less at random. They do not form crystals.

### Vocabulary

• solid: State of matter that has a fixed volume and fixed shape.

### Practice

1. According to the article, what is the only way the shape of a solid can be changed? Give an example.
2. Describe the analogy in the article in which crystalline and amorphous solids are compared to a classroom.

### Review

1. What is a solid?
2. Why does a solid have a fixed shape and fixed volume?
3. Create a table comparing and contrasting crystalline and amorphous solids. Include an example of each type of solid in your table.
4. Diamonds like the one pictured in the Figure below are the hardest of all minerals. Is a diamond a crystalline or an amorphous solid? How do you know?

### Notes/Highlights Having trouble? Report an issue.

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