Scientists Say: Crystal | Science News for Students

Scientists Say: Crystal

This a material whose atoms or molecules are arranged in a 3-D pattern
Sep 30, 2019 — 6:30 am EST
a close-up photo of a citrine crystal

This “citrine” crystal is mostly made of silicon and oxygen arranged in a particular pattern. Like other crystals, its chemical building blocks repeat regularly.    

Nastya22/iStock/Getty Images Plus

Crystal (noun, “KRIS-tal”)

This is a solid made of atoms or molecules arranged in a 3-D pattern. Materials of this sort are called “crystalline.” If you could zoom way in to look inside a crystalline material, you’d see a repeating building block. This building block is called a “unit cell.” In the common crystal table salt, or sodium chloride, the sodium and chlorine atoms arrange in a cube-shaped unit cell. But unit cells come in other shapes too. Some are hexagonal prisms. Others are more like a cube that’s had its top pushed over.

One way scientists figure out the positions of atoms or molecules in a crystal is by blasting them with X-rays. The way X-rays scatter when colliding with a material can reveal how the parts are stacked up.

The word “crystal” brings gems to mind, for good reason. A lot of gemstones are crystals. For example, a diamond is a crystal made of carbon atoms in a repeating pattern. Some people attribute special healing powers to crystals. But there’s no evidence that those expensive rocks can protect someone any more than the salt in the shaker on the counter.

In a sentence

Nanowires made by stretching single crystals of silver could help engineers make bendy electronics.

Check out the full list of Scientists Say.

Power Words

(more about Power Words)

3-D     Short for three-dimensional. This term is an adjective for something that has features that can be described in three dimensions — height, width and length. 

atom     The basic unit of a chemical element. Atoms are made up of a dense nucleus that contains positively charged protons and uncharged neutrons. The nucleus is orbited by a cloud of negatively charged electrons.

carbon     The chemical element having the atomic number 6. It is the physical basis of all life on Earth. Carbon exists freely as graphite and diamond. It is an important part of coal, limestone and petroleum, and is capable of self-bonding, chemically, to form an enormous number of chemically, biologically and commercially important molecules.

chlorine     A chemical element with the scientific symbol Cl. It is sometimes used to kill germs in water. Compounds that contain chlorine are called chlorides.

crystal     (adj. crystalline) A solid consisting of a symmetrical, ordered, three-dimensional arrangement of atoms or molecules. It’s the organized structure taken by most minerals. Apatite, for example, forms six-sided crystals. The mineral crystals that make up rock are usually too small to be seen with the unaided eye.

diamond     One of the hardest known substances and rarest gems on Earth. Diamonds form deep within the planet when carbon is compressed under incredibly strong pressure.

glass     A hard, brittle substance made from silica, a mineral found in sand. Glass usually is transparent and fairly inert (chemically nonreactive). Aquatic organisms called diatoms build their shells of it.

molecule     An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2); water is made of two hydrogen atoms and one oxygen atom (H2O).

nanowire     A wire or rod on the order of a billionth of a meter in cross-section or in circumference. It is usually made from some type of semiconducting material. However some bacteria make string-like anchoring structures on the same size scale. Like the semiconductor wire, the bacterial ones also can transport electrons.

random     Something that occurs haphazardly or without reason, based on no intention or purpose.

salt     A compound made by combining an acid with a base (in a reaction that also creates water). The ocean contains many different salts — collectively called “sea salt.” Common table salt is a made of sodium and chlorine.

sodium     A soft, silvery metallic element that will interact explosively when added to water. It is also a basic building block of table salt (a molecule of which consists of one atom of sodium and one atom of chlorine: NaCl). It is also found in sea salt.

solid     Firm and stable in shape; not liquid or gaseous.

X-ray     A type of radiation analogous to gamma rays, but having somewhat lower energy.