[عاطف خليفة]

Matter

absorption. absorb; absorbent. Compare with adsorption and sorption. 1. Penetration of molecules into the bulk of a solid or liquid, forming either a solution or compound. Absorption can be a chemical process (a strong solution of NaOH absorbs CO2 from the air) or a physical process (palladium absorbs hydrogen gas). 2. Capture and transformation of energy by a substance; for example, copper looks reddish because it absorbs blue light. An absorbent captures another material and distributes it throughout; an adsorbent captures another material and distributes it on its surface only.
adsorbent. Compare with absorbent. A substance that collects molecules of another substance on its surface. For example, gases that make water taste bad are strongly adsorbed on activated charcoal granules in water filters.
adsorption. adsorb; adsorbed. Compare with absorption and sorption. Adsorption is collection of a substance on the surface of a solid or a liquid. For example, gases that make water taste bad are strongly adsorbed on charcoal granules in water filters.
aeration. aerate. Preparation of a saturated solution of air gases by either spraying the solution in air or by bubbling air through it.
aerosol. Compare with colloid. A colloid in which solid particles or liquid droplets are suspended in a gas. Smoke is an example of a solid aerosol; fog is an example of a liquid aerosol.
alkali metal. (alkaline earth metal) alkali metal element. The Group 1 elements, lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr) react with cold water for form strongly alkaline hydroxide solutions, and are referred to as "alkali metals". Hydrogen is not considered an alkali metal, despite its position on some periodic tables.
alkaline earth. An oxide of an alkaline earth metal, which produces an alkaline solution in reaction with water.
alkaline earth metal. (alkali metal) The Group 2 elements, beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra) form alkaline oxides and hydroxides and are called "alkaline earth metals".
allotrope. allotropy; allotropic; allotropism. Compare with isotope and polymorph. Some elements occur in several distinct forms called allotropes. Allotropes have different chemical and physical properties. For example, graphite and diamond are allotropes of carbon.
alloy. alloying; alloyed. Compare with amalgam. A mixture containing mostly metals. For example, brass is an alloy of copper and zinc. Steel contains iron and other metals, but also carbon.
amalgam. Compare with alloy. An alloy that contains mercury.
analysis. chemical analysis. Determination of the composition of a sample.
atom. Compare with molecule and ion. An atom is the smallest particle of an element that retains the chemical properties of the element. Atoms are electrically neutral, with a positively charged nucleus that binds one or more electrons in motion around it.
boiling. Conversion of liquid into gas as bubbles of gas that form within the liquid. Boiling begins at the temperature where the vapor pressure of a liquid would be equal to the external pressure on the liquid.
boiling point. (bp) standard boiling point; normal boiling point. The temperature at which the vapor pressure of a liquid would be equal to the external pressure on the liquid. The standard boiling point is the temperature at which the vapor pressure of a liquid equals standard pressure.
chemical change. reaction; chemical reaction. Compare with physical change. A chemical change is a dissociation, recombination, or rearrangement of atoms.
chemical property. chemical properties. Compare with physical property. Measurement of a chemical property involves a chemical change. For example, determining the flammability of gasoline involves burning it, producing carbon dioxide and water.
chromatography. Chromatography is a method for separating mixtures based on differences in the speed at which they migrate over or through a stationary phase.
colloid. A colloid is a heterogeneous mixture composed of tiny particles suspended in another material. The particles are larger than molecules but less than 1 µm in diameter. Particles this small do not settle out and pass right through filter paper. Milk is an example of a colloid. The particles can be solid, tiny droplets of liquid, or tiny bubbles of gas; the suspending medium can be a solid, liquid, or gas (although gas-gas colloids aren't possible).
column chromatography. Column chromatography is a method for separating mixtures. A solution containing the mixture is passed through a narrow tube packed with a stationary phase. Different substances in the mixture have different affinities for the stationary phase, and so move through the tube at different rates. This allows the substances in the mixture to be detected or collected separately as they reach the end of the tube.
compound Compare with element and mixture. A compound is a material formed from elements chemically combined in definite proportions by mass. For example, water is formed from chemically bound hydrogen and oxygen. Any pure water sample contains 2 g of hydrogen for every 16 g of oxygen.
concentration. Compare with dilution. 1. A measure of the amount of substance present in a unit amount of mixture. The amounts can be expressed as moles, masses, or volumes. 2. The process of increasing the amount of substance in a given amount of mixture.
condensation. condensed. 1. The conversion of a gas into a liquid is called condensation. Condensation usually occurs when a gas is cooled below its boiling point. 2. A reaction that involves linking of two molecules with the elimination of water (or another small molecule).
congener. 1. Elements belonging to the same group on the periodic table. For example, sodium and potassium are congeners. 2. Compounds produced by identical synthesis reactions and procedures.
crystallization. fractional crystallization; crystallisation. The process of forming pure crystals by freezing a liquid, evaporating a solution, or precipitating a solid from solution. Impurities remain in the liquid, so crystallization is often to purify solid substances.
density. (,d) Compare with specific gravity. Mass of a substance per unit volume. Saying "the density of mercury is 13.55 g/cm3 " is the same as saying "the mass of exactly 1 cm3 of mercury is 13.55 g".
dialysis. Dialysis is the separation of components in a mixture by passing them across a semipermeable membrane.
diffusion. diffuse. Compare with effusion. The mixing of two substances caused by random molecular motions. Gases diffuse very quickly; liquids diffuse much more slowly, and solids diffuse at very slow (but often measurable) rates. Molecular collisions make diffusion slower in liquids and solids.
dilution. Adding solvent to a solution to lower its concentration.
distillate. The vapor collected and condensed from a distillation.
distillation. Distillation is a technique for separating components of a mixture on the basis of differing boiling points. The mixture is heated, vaporizing some of the components. The vapor is collected and condensed to isolate the components with the lowest boiling points.
ductile. ductility. Compare with malleable. Capable of being drawn into wire. Metals are typically ductile materials.
electrolysis. The process of driving a redox reaction in the reverse direction by passage of an electric current through the reaction mixture.
electrorefining. Electrorefining is a method for purifying a metal using electrolysis. An electric current is passed between a sample of the impure metal and a cathode when both are immersed in a solution that contains cations of the metal. Metal is stripped off the impure sample and deposited in pure form on the cathode.
element Compare with compound and mixture. An element is a substance composed of atoms with identical atomic number. The older definition of element (an element is a pure substance that can't be decomposed chemically) was made obsolete by the discovery of isotopes.
element symbol. An international abbreviation for element names, usually consisting of the first one or two distinctive letters in element name. Some symbols are abbreviations for ancient names.
emulsion. Compare with colloid. A colloid formed from tiny liquid droplets suspended in another, immiscible liquid. Milk is an example of an emulsion.
evaporation. vaporization. Conversion of a liquid into a gas.
evaporate. To convert a liquid into a gas.
extensive property. extensive; extensive properties. Compare with intensive property. A property that changes when the amount of matter in a sample changes. Examples are mass, volume, length, and charge.
extraction. A technique for separating components in a mixture that have different solubilities. For example, caffeine can be separated from coffee beans by washing the beans with supercritical fluid carbon dioxide; the caffeine dissolves in the carbon dioxide but flavor compounds do not. Vanillin can be extracted from vanilla beans by shaking the beans with an organic solvent, like ethanol.
foam. Compare with colloid. A colloid in which bubbles of gas are suspended in a solid or liquid. Aerogel (solid smoke) and Styrafoam are examples of solid foams; whipped cream is an example of a liquid foam.
fractional distillation. Compare with distillation. A technique for separation of liquid mixtures by distillation that uses a tower attached to a flask containing the mixture to perform multiple distillations. Vapor moving up the column condenses on packing material inside the column, trickles down the column, and again vaporises. The more volatile component can then be drawn off at the top of the component, while the less volatile component remains at the bottom.
gas. gases; vapor. Matter in a form that has low density, is easily compressible and expandable, and expands spontaneously when placed in a larger container. Molecules in a gas move freely and are relatively far apart. "Vapor" often refers to a gas made of a substance that is usually encountered as a liquid or solid; for example, gaseous H2O is called "water vapor".
gel. Compare with colloid. A gell is a sol in which the solid particles fuse or entangle to produce a rigid or semirigid mixture. For example, gelatin dissolved in water produces a sol of protein molecules. When the gelatin is cooked, the protein chains entangle and crosslink, forming a gel which is a mesh of solid protein with trapped pockets of liquid inside. Fruit jellies are also gels
group. 1. A substructure that imparts characteristic chemical behaviors to a molecule, for example, a carboxylic acid group. (also: functional group). 2. A vertical column on the periodic table, for example, the halogens. Elements that belong to the same group usually show chemical similarities, although the element at the top of the group is usually atypical.
heterogeneous mixture. heterogeneous. Compare with homogeneous mixture, solution, element, and compound. A sample of matter consisting of more than one pure substance and more than one phase. Blood, protoplasm, milk, chocolate, smoke, and chicken soup are examples of heterogeneous mixtures.
high performance liquid chromatography. HPLC. An efficient form of column chromatography that pumps a liquid solution of the sample at very high pressure through a column packed with a stationary phase made of very tiny particles. The high pressure pumps required make HPLC an expensive technique.
homogeneous mixture. solution. Compare with heterogeneous mixture, element and compound. A sample of matter consisting of more than one pure substance with properties that do not vary within the sample.
intensive property. intensive; intensive properties. Compare with extensive property. A property that does not change when the amount of sample changes. Examples are density, pressure, temperature, color.
ion exchange. ion exchange resin; ion exchanger. Ion exchange is a method of separating ions from a solution by reversibly binding them onto a resin that has charged sites on its surface. Ion exchangers are used to remove metal ions from drinking water.
kinetic energy. Compare with potential energy. The energy an object possesses by virtue of its motion. An object of mass m moving at velocity v has a kinetic energy of ½mv2.
lanthanide. Compare with actinide and inner transition metals. Elements 57-70 are called lanthanides. Electrons added during the Aufbau construction of lanthanide atoms go into the 4f subshell.
law of conservation of mass. There is no change in total mass during a chemical change. The demonstration of conservation of mass by Antoine Lavoisier in the late 18th century was a milestone in the development of modern chemistry.
law of definite proportions. When two pure substances react to form a compound, they do so in a definite proportion by mass. For example, when water is formed from the reaction between hydrogen and oxygen, the 'definite proportion' is 1 g of H for every 8 g of O.
law of multiple proportions. When one element can combine with another to form more than one compound, the mass ratios of the elements in the compounds are simple whole-number ratios of each other. For example, in CO and in CO2, the oxygen-to-carbon ratios are 16:12 and 32:12, respectively. Note that the second ratio is exactly twice the first, because there are exactly twice as many oxygens in CO2 per carbon as there are in CO.
liquid. A state of matter that has a high density and is incompressible compared to a gas. Liquids take the shape of their container but do not expand to fill the container as gases do. Liquids diffuse much more slowly than gases.
malleable. malleability. Compare with ductile. Capable of being hammered into sheets. Metals are typically malleable materials.
mass. (m) Compare with weight. Mass is a measure of the tendency of an object to resist acceleration. It's harder to roll a tractor trailer than a roller skate; the tractor trailer has a far greater mass.
matter. Matter is anything that has mass. Air, water, coffee, fire, human beings, and stars are matter. Light, X-rays, photons, gravitons, information, and love aren't matter.
metal. metallic. Compare with nonmetal and metalloid. A metal is a substance that conducts heat and electricity, is shiny and reflects many colors of light, and can be hammered into sheets or drawn into wire. Metals lose electrons easily to form cations. About 80% of the known chemical elements are metals.
molecule. Compare with atom and ion. The smallest particle of an element or compound that retains the chemical properties of the element or compound. A molecule is a collection of chemically bound atoms with characteristic composition and structure. Making or breaking bonds in a molecule changes it into a new molecule. Ionic compounds are not composed of molecules, because there is no distinct collection of ions that are chemically bound in the crystal.
nonparticulate. Not composed of distinct particles.
nonmetal. (metal,metalloid) non-metal. A nonmetal is a substance that conducts heat and electricity poorly, is brittle or waxy or gaseous, and cannot be hammered into sheets or drawn into wire. Nonmetals gain electrons easily to form anions. About 20% of the known chemical elements are nonmetals.
nonpolar. Having a relatively even or symmetrical distribution of charge.
nonpolar molecule. A molecule in which the center of positive charge and the center of negative charge coincide. Examples are CCl4 and CO2; counterexamples are CHCl3 and H2O.
particulate. Composed of distinct particles. Smoke is particulate; pure gases are not.
periodic table. An arrangement of the elements according to increasing atomic number that shows relationships between element properties.
period. Rows in the periodic table are called periods. For example, all of the elements in the second row are referred to as 'second period elements'. All elements currently known fall in the first seven periods.
phase. in phase; out of phase; wave phase. 1.A phase is a part of a sample of matter that is in contact with other parts but is separate from them. Properties within a phase are homogeneous (uniform). For example, oil and vinegar salad dressing contains two phases: an oil-rich liquid, and a vinegar-rich liquid. Shaking the bottle breaks the phases up into tiny droplets, but there are still two distinct phases. 2. In wave motion, phase is the fraction of a complete cycle that has passed a fixed point since the current cycle began. The phase is often expressed as an angle, since a full cycle is 360^deg; (2 ). Two waves are "in phase" if the peaks of one wave align with the peaks of the other; they are "out of phase" if the peaks of one wave align with the troughs of the other.
phase boundary. A phase boundary is a surface where two samples of matter with different properties are in contact. The surface of a gas bubble in water or the surface of a crystal are examples of phase boundaries.
physical change. Compare with chemical change. A change which does not transform one substance into another. For example, freezing water is a physical change because both water and ice are H2O. However, electrolysis of water would not be a physical change because passing a strong electric current through water can decompose it into H2 and O2.
physical property. physical properties. Compare with chemical property. Measurement of a physical property may change the arrangement but not the structure of the molecules of a material. Examples of physical properties are density, color, boiling point, volume, temperature, and mass.
plasma. 1. In biology, the fluid in which blood cells or lymph cells are suspended. 2. A gaslike state of matter consisting of positively charged ions, free electrons, and neutral particles. Plasma is found in stars, the sun, the solar wind, lightning, and fire.
polymorph. polymorphism; polymorphic. Compare with isotope and allotrope. Solid substances that occur in several distinct forms. Polymorphs have different chemical and physical properties. allotropes are polymorphs of elements.
potential energy. Compare with kinetic energy. energy an object possesses by virtue of its position. For example, lifting a mass mby h meters increases its potential energy by mgh, where g is the acceleration due to gravity.
precipitate. () ppt. An insoluble substance that has been formed from substances dissolved in a solution. For example, mixing silver nitrate and sodium chloride solutions produces a precipitate, insoluble silver chloride (along with soluble sodium nitrate.
precipitation. Precipitation is the conversion of a dissolved substance into insoluble form by chemical or physical means.
pure substance. substance. A sample of matter that cannot be separated into simpler components without chemical change. Physical changes can alter the state of matter but not the chemical identity of a pure substance. Pure substances have fixed, characteristic elemental compositions and properties.
qualitative analysis. Compare with quantitative analysis. A chemical analysis that detects the presence of a substance in a sample.
quantitative analysis. Compare with qualitative analysis. A chemical analysis that determines the concentration of a substance in a sample.
sedimentation. Separation of a dense material (usually a solid) from a less dense material (usually a liquid) by allowing the denser material to settle out of the mixture.
semipermeable membrane. A membrane that allows some but not all of the components in a mixture to pass through it. Semipermeable membranes are used in dialysis.
sol. A colloid with solid particles suspended in a liquid. Examples are protoplasm, starch in water, and gels.
solid. A solid is a relatively dense, rigid state of matter, with a definite volume and shape. Molecules in solids are often packed close together in regularly repeating patterns, and vibrate around fixed positions.
soluble. Compare with insoluble. Capable of being dissolved in a solvent (usually water).
soluble salt. An ionic compound that dissolves in a solvent (usually water).
solution. homogeneous mixture. Compare with heterogeneous mixture. A sample of matter consisting of more than one pure substance with properties that do not vary within the sample. Also called a homogeneous mixture.
solvent. The most abundant component in a solution.
solvent extraction. Solvent extraction is a method for separating mixtures by exploiting differences in the solubilities of the components. For example, a coffee machine extracts the soluble components of ground coffee with water, and leaves the insoluble components behind. The sample is shaken or mixed with solvent (or with two immiscible solvents) to effect the separation. The "like dissolves like" is a useful guide for selecting solvents to use in the extraction. Nonpolar substances are usually successfully extracted into nonpolar solvents like hexane or methylene chloride. Polar and ionic substances are often extracted with water.
sorption. Compare with adsorption and absorption. Assimilation of molecules of one substance by a material in a different phase. Adsorption (sorption on a surface) and absorption (sorption into bulk material) are two types of sorption phenomena.
state of matter. There are three common states of matter: gases, liquids, and solids. States of matter differ in the way the molecules are arranged at the molecular level, but not in the structure of the molecules themselves. Other states (the plasma and Bose-Einstein condensate states) are uncommon on Earth.
stationary phase. A stationary phase is a substance that shows different affinities for different components in a sample mixture in a separation of the mixture by chromatography. The mobile phase (a solution containing the sample) flows over or through the stationary phase to effect the separation.
stoichiometry. 1. Ratios of atoms in a compound. 2. Ratios of moles of compounds in a reaction. 3. A branch of chemistry that quantitatively relates amounts of elements and compounds involved in chemical reactions, based on the law of conservation of mass and the law of definite proportions.
stripping. Stripping is a technique for removing volatile components in a mixture by bubbling a stream of an chemically unreactive gas (like nitrogen) through the sample, and then 'scrubbing' the nitrogen through a solution or solid adsorbent that can recover the volatile materials.
sublimation. sublimate; sublimating. Conversion of a solid directly into a gas, without first melting into a liquid.
thin layer chromatography. (TLC) Compare with chromatography. A technique for separating components in a mixture on the basis of their differing polarities. A spot of sample is placed on a flat sheet coated with silica and then carried along by a solvent that soaks the sheet. Different components will move different distances over the surface. TLC is a useful screening technique in clinical chemistry; for example, it can be used to detect the presence of drugs in urine.
transition metal. transition element; outer transition element. An element with an incomplete d subshell. Elements which have common cations with incomplete d subshells are also considered transition metals. Elements with incomplete f subshells are sometimes called "inner transition elements".
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.