This video explains how the molecular structure of diamonds and graphite determines their properties (4:19 min.) This causes the atoms to become packed together in the tightest crystalline state possible. Why are these carbon atoms packed so tightly together? It is because diamonds are formed deep within the Earth, when very high pressure is applied to carbon. In diamonds, every carbon atom is bound to four other carbon atoms in the tightest possible combination. In graphite, the carbon atoms form sheets that are layered on top of each other. So, how can two materials that are so different be made of the same atoms? The difference is in their crystal structure. What is amazing about these two crystals? They are both made up of only carbon! Meanwhile, graphite is dark, opaque and so soft that tiny bits of it are rubbed onto paper when you use a pencil. For example, diamonds are transparent and so strong they can cut through glass. This becomes clear when we compare crystals made from carbon. The crystal structure is just as important to the crystal as the molecules are. Molecular structures and photographs of quartz, salt crystals and ice crystals (Let’s Talk Science using images: Quartz structure by Ben Mills via Wikimedia Commons, Quartz crystal: JJ Harrison via Wikimedia Commons, Salt crystal by Ravodina Anastasia via Wikimedia Commons and Ice crystal by Thomas Bresson via Wikimedia Commons). These water molecules form flat hexagonal plane crystals. It is is made up of water (H 2O) molecules. Quartz crystals, which are made up of silicon dioxide (SiO 2) molecules, form hexagonal prisms with hexagonal pyramids on either end. Table salt naturally forms cubic crystals. These molecular compositions form structures of different shapes. It's very repetitive, which is exactly what makes it a crystal!ĭifferent minerals have different molecular compositions. Each chlorine ion is surrounded by six sodium ions. Each sodium ion is surrounded by six chlorine ions. For example, in the case of table salt (NaCl), the crystals are made up of cubes of sodium (Na) ions and chlorine (Cl) ions. In a crystal, all of the atoms (or ions) are arranged in a regular grid pattern. What all crystals have in common is an extremely well-organized molecular structure. Graphite in pencils, table salt, and snow are crystals, too. But those are not the only types of crystals. When we hear the word "crystals," we usually think of coloured minerals. Open Professional Learning × Close Professional Learning Open Educational Resources × Close Educational Resources
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