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Thursday, May 16, 2024

Awesome, Hypnotic Photos of Swirling, Crystal Chemistry

If you memorized the periodic table, if you whipped up exothermic reactions in your kitchen, Wenting Zhu and Yan Liang are here to renew your relationship with the elements.

To generate the images in their 300-photo collection The Beauty of Chemistry, out today, Zhu and Liang utilized infrared thermal imaging techniques, along with high-speed and time-lapse micro photography to plunge readers into the minute world of molecules and the often stunning reactions between them. With atomic clarity, science writer Philip Ball narrates this visual tour through the under-appreciated chemical beauty that surrounds us, from describing the principles that generate the unique symmetry of a snowflake to connecting the lifelike tendrils created by silicate salts to the origins of life itself.


Perhaps the most basic—and astonishing— of these concepts is the hydrogen bond, which holds together the literal stuff of life: water. Each water molecule is comprised of two hydrogen atoms bonded to an oxygen atom, but oxygen has six electrons in its outer shell. Only two electrons are needed to form that chemical bond with hydrogen, so four negatively charged electrons, grouped by twos in “dangling” pairs, are hovering out there in micro-space hoping for a way to balance themselves out. These pairs pull weakly on the hydrogen atoms bonded to neighboring water molecules, forming brief, one-trillionth-of-a-second bonds before breaking and reforming with another hydrogen atom. And it’s this constant, unceasing dance that allows for the chemical motion that makes life possible, what Ball calls a “molecular dialog” that hovers between order and chaos.

This chromium hydroxide precipitate is in the process of solidifying as it swirls and dilutes within its container. This reaction occurs when two liquid compounds, containing both positively and negatively charged ions, come together and perform a molecular reel, in which they trade partners. In this case, chromium chloride and sodium hydroxide swap ions. The positively charged chromium and negatively charged hydroxide molecules are attracted to one another because they balance out energetically. They form tight bonds that freeze the molecules into place, creating a solid byproduct that doesn’t have room for all those water molecules to fit neatly. The reaction also creates sodium chloride, commonly known as table salt, which dissolves in water just fine.

Crystals are the pinnacle of atomic efficiency—from a tiny seed of highly organized atoms, their structure grows as more of the surrounding molecules repeat the same pattern and build on each other. Copper sulfate crystals, like the one pictured above, are also easy for would-be chemists to make at home with a few ingredients and a bit of patience.

Dendritic growth, like that pictured above, is a type of crystallization that forms branching, tree-like structures instead of a large crystal mass. Above, nicotinic acid (also known as the essential vitamin niacin) forms dandelion-like crystal structures after a supersaturated solution of the acid is cooled very rapidly. The physical process for forming dendrites is essentially the same as crystallization, only sped up by a sudden change in temperature or chemical composition.

What you see here is a potassium dichromate solution crystalizing as the surrounding water rapidly evaporates. The patterns themselves are created by variations in the solution. This is an example of what’s called growth instability, in which certain areas tend to aggregate more particles and crystalize faster, making for elaborate fractal patterns.

First discovered by a German chemist named Raphael Liesegang in 1986, these odd-looking rings are the result of a precipitation reaction in gel. Silver nitrate is added to a petri dish containing potassium dichromate. The two compounds precipitate, or trade ions, and create silver chromate where they meet. There are competing theories as to why these rings form, but many scientists believe that the initial deposit of silver chromate becomes supersaturated and diffuses through the gel to create a new chemical pile-up zone, where the concentration becomes saturated once again, forming concentric rings.

Potassium permanganate, also known as the “chameleon mineral,” is an ultra-positively charged compound known as an oxidizing agent. Oxygen on its own likes to borrow electrons from surrounding atoms. In a sugar solution, the oxygen in potassium permanganate pulls electrons from the sugar molecules, creating a “redox” reaction. As the permanganate gains electrons and gets closer to chemical equilibrium, it changes color from purple to green to blue to reddish brown.

This hollow branch of ammonium iron sulfate is suspended within a chemical garden—a silicate solution full of dissolved iron salts that then precipitate out. Because silicate ions tend to form long chains and sheets, they turn a typical precipitation reaction into a process that generates an inorganic garden full of angled branches and vibrant blooms. As iron salts trade ions with the surrounding solution and solidify, they form a thin, hollow membrane with a water-filled interior that is less dense than the liquid outside. As pressure builds inside these tubes, they branch out and grow in unpredictable ways.

Updated 5-13-21, 4:30 pm EST: The caption for an image of potassium dichromate crystallization was updated.

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