Crystal Formation Task

Lexie Coleman


Initial Research Questions

1. What is a crystal? A piece of a solid substance having a naturally geometrically regular form with symmetrically arranged plane faces.

    2. What substances can be used to make crystals? Crystals structure is a unique arrangement of atoms or molecules in a liquid or solid. A crystal structure is composed of a pattern, a set of atoms arranged in a particular way, and a lattice. Patterns are located upon the points of a lattice, which is an array of points.

    3. What are some examples of crystals in nature? What household items can you also grow crystals from? Arranged in a consistent repeating pattern, creating one of seven geometrical shapes. Crystals can be expensive and beautiful, like diamonds, but they can also be found right in your kitchen in the form of sugar and salt!

    4. Explain the process of crystal growth. A crystal is a solid material whose atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. Crystal growth is a major stage of a crystallization process, and consists in the addition of new atoms, ions. The growth typically follows an initial stage of either homogeneous or heterogeneous (surface catalyzed) nucleation, unless a "seed" crystal, purposely added to start the growth, was already present.

    5. Explain how crystals can grow in different shapes and sizes. If there is a highly attractive interaction (energetically speaking) along a certain direction of a crystal, then that direction will probably grow fast. However, it could also grow slowly, if that direction interacted strongly with the solvent; having strongly absorbed solvent on the surface of the crystal could block growth along that face.

    6. Outline a few different types of crystals. Covalent Crystals: This is a crystal which has real chemical covalent between all of the atoms in the crystal. So really a single crystal of covalent crystals is really just one big molecule. An example of this is a crystal like a diamond. Covalent crystals can have extremely high melting points.

    Metallic Crystals: Individual metal atoms sit on lattice sites while the outer electrons from these atoms are able to flow freely around the lattice. Metallic crystals normally have high melting points.

    Ionic Crystals: This is a crystal where the individual atoms do not have covalent bonds between them, but are held together by electrostatic forces. An example of this type of crystal is sodium chloride (NaCl). Ionic crystals are hard and have relatively high melting points.

    7. What effect do crystals have on light travelling through them? (relate to reflection, refraction, dispersion and diffraction) Crystal optics is the branch of optics that describes the behaviour of light in anisotropic media, such as crystals in which light behaves differently depending on which direction the light is coming from. The index of refraction depends on both composition and crystal structure and can be calculated using the Gladstone-Dale relation. Crystals are often naturally anisotropic, and in some media (such as liquid crystals) it is possible to induce anisotropy by applying an external electric field.

    8. What are the optimum conditions for crystal growth? Warmth is the key to forming crystals; the jar's surroundings should be warm also for optimum crystal growth. Warm air temperature aids water evaporation, causing the crystals to grow more quickly. Crystals will still grow in cooler temperatures, but it will take much longer for the water to evaporate.

    Crystal growth also requires light. Again, the crystals will eventually grow in the dark, but it will take a very long time. Light evaporates water as heat does; combine them by placing your jar on a warm, sunny windowsill and you should have crystals in a few days.

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