subject
Chemistry
How matter is structured and transformed at the molecular scale, with attention to the reasoning behind chemical concepts rather than memorization.
12 lessons in chemistry
Endothermic and Exothermic Reactions
Snap a glow stick and it gets a little cooler in your hand. Light a match and your fingers feel the heat almost immediately. Both are chemical reactions. So why does one pull warmth in and the other p…
3 min · comparison
How Equilibrium Shifts Under Pressure: Le Chatelier's Principle
Imagine a sealed steel cylinder containing a mixture of nitrogen, hydrogen, and ammonia, sitting at equilibrium.
4 min · deepening
How Catalysts Speed Reactions Without Being Consumed
Drop a small piece of platinum gauze into a flask of hydrogen and oxygen at room temperature, and within seconds the mixture ignites.
4 min · foundation
How Soap Cleans Dirt and Oil
Rinse a greasy pan under plain water and watch what happens. The water beads up on the oil and runs off, leaving the grease behind. Add a squirt of soap, scrub for a few seconds, and the same oil disa…
3 min · deepening
Ionic and Covalent Bonds: Two Ways Atoms Hold Together
Drop a pinch of table salt into water and watch it vanish. The crystal — sodium chloride — does not melt or float; it dissociates, releasing sodium and chloride as separate charged particles that drif…
4 min · comparison
What an Acid Actually Is: The Brønsted-Lowry View
Drop a tablet of vitamin C into a glass of water and something quietly remarkable happens.
4 min · foundation
Why Entropy Tends to Increase
Drop a single drop of ink into a glass of still water and walk away.
4 min · deepening
Why Metal Rusts (and Gold Doesn't)
Leave an iron nail in a glass of water for a week. When you pull it out, the surface is rough, orange, and flaking. Leave a gold ring in that same glass for a year, and it will look exactly the same a…
3 min · foundation
Why Salt Melts Ice
On a cold morning, the road crew drives by and scatters white pellets across the icy pavement.
3 min · foundation
Why the Periodic Table Is Periodic
Mendeleev arranged the elements by mass in 1869 and noticed something strange: chemical behavior repeated.
4 min · synthesis
Why Things Burn: The Combustion Triangle
Strike a match and watch the head flare. Hold the flame to a candle wick, and the wick catches. Blow on it gently and it burns brighter. Cap the candle with a glass jar, and within seconds the flame s…
3 min · foundation
Why Water Has Such Strange Properties
Drop an ice cube into a glass of water and watch it float. This is so familiar that it takes effort to notice how strange it is. Almost every other substance on Earth contracts when it freezes, so the…
4 min · foundation