Glossary - Xx Yy Zz
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| Xenobiotic | A substance which is not normally found in a living thing. |
| Xenon | Xe. Element 54, a colourless, inert gas used to fill cathode ray tubes. |
| X-ray | A very high energy form of electromagnetic radiation (though not as high energy as gamma rays). X-rays typically have wavelengths from a few picometres up to 20 nanometres. X-rays easily penetrate soft tissue, which makes them useful in medical imaging and in radiation therapy. |
| X-ray crystallography | Determination of three dimensional arrangement of atoms in a crystal by analysis of x-ray diffraction patterns. |
| X-ray diffraction pattern | Interference patterns created by x-rays as they pass through a solid material. Studying x-ray diffraction patterns gives detailed information on the three-dimensional structure of crystals, surfaces, and atoms. |
| X-ray spectrum | x-ray spectra. A set of characteristic x-ray frequencies or wavelengths produced by a substance used as a target in an x-ray tube. Each element has a characteristic x-ray spectrum, and there is a strong correlation between atomic number and the frequencies of certain lines in the x-ray spectrum. |
| X-ray tube | A cathode ray tube that focuses energetic streams of electrons on a metal target, causing the metal to emit x-rays. |
| Yield | experimental yield; actual yield. The amount of product actually obtained in a chemical reaction. |
| Ytterbium | Yb. Element 70, atomic weight 173.04, a very rare, malleable metal used in special alloys for X-ray sources. |
| Yttrium | Y. Element 39, atomic weight 88.90585, a dark grey metal that is used in alloys and nuclear technology for its high neutron transparency. Yttrium compounds are used in the manufacture of colour TV screens, superconducting ceramics, and fireproof bricks. |
| Zeeman effect | The splitting of spectral lines when an external magnetic field is applied. |
| Zeta potential | electrokinetic potential. Electric potential across all phase boundaries between solids and liquids. In colloids, the zeta potential is the potential across the ion layer around a charged colloidal particle. Neutralizing the zeta potential can cause the colloid to precipitate. |
| Zeolite | Addition compounds of the type Na2O·Al2O3·n SiO2·m H2O, with calcium sometimes replacing or present with the sodium. The sodium in the zeolite exchanges with calcium in water, making zeolites useful for water softening. The porous structure of zeolites also makes them effective molecular sieves used as gas adsorbents and drying agents. Artificial zeolites are used as ion exchange resins. |
| Zero order reaction | A reaction with a reaction rate that does not change when reactant concentrations change. |
| Zero point energy | A minimum possible energy for an atom or molecule predicted by quantum mechanics. Electrons stay in motion and bonds continue to vibrate even at absolute zero because of zero point energy. |
| Zinc | Zn. Element 30, atomic weight 65.37, a reactive grey metal that dissolves in acids, used to galvanize metals and in many alloys (e. g. brass and bronze). |
| Zincography | Process of etching unprotected parts of a zinc plate with strong acids to produce a printing surface. |
| Zirconium | Zr. Element 40, atomic weight 91.22, a hard, greyish, highly flammable crystalline metal that dissolves in hot concentrated acids. Used in steel manufacture and in nuclear reactor chambers because of its transparency to neutrons. Its silicate is used to make zircon used as a gemstone. |
| Zone refining | A method for purifying solids based on the fact that solutes tend to concentrate in the liquid when a solution is frozen. A solid bar is drawn slowly over a heat source and melted in a narrow band; impurities are carried along in the melted band until the end of the bar is reached. |
| Zwitterion | A particle that contains both positively charged and negatively charged groups. For example, amino acids (NH2-CHR-COOH) can form zwitterions (+NH3-CHR-COO-). |
| Zymase | Enzymes present in yeast that catalyse fermentation of sugar into alcohol and carbon dioxide. |
| Zymogen | proenzyme. A protein that may be converted into an enzyme. |
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