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Home Glossary

# Glossary: I

Glossary
incomplete combustion.
A combustion reaction or process that does not convert all of the fuel's carbon and hydrogen into carbon dioxide and water, respectively. For example, incomplete combustion of carbon produces carbon monoxide.

incomplete octet.
1. An atom with less than eight electrons in its valence shell. 2. An atom with less than eight total bonding and nonbonding electrons in a Lewis structure, for example, B in BH3 has an incomplete octet.

ideal gas. ideal gases; perfect gas; ideal gas law.
A gas whose pressure P, volume V, and temperature T are related by PV = nRT, where n is the number of moles of gas and R is the ideal gas law constant. Ideal gases have molecules with negligible size, and the average molar kinetic energy of an ideal gas depends only on its temperature. Most gases behave ideally at sufficiently low pressures.

ideal gas law constant. (R) ideal gas constant; universal gas constant.
A constant R equal to PV/(nT) for ideal gases, where the pressure, volume, moles, and temperature of the gas are P, V, n, and T, respectively. The value and units of R depend on the units of P, V, and T. Commonly used values and units of R include: 82.055 cm3 atm K-1 mol-1; 0.082055 L atm mol-1 K-1; 8.31434 J mol-1 K-1; 1.9872 cal K-1 mol-1; 8314.34 L Pa mol-1 K-1; 8.31434 Pa m3 mol-1 K-1.

ideal solution.
All molecules in an "ideal solution" interact in exactly the same way; the solvent-solvent, solvent-solute, and solute-solute intermolecular forces are all equivalent. Ideal solutions obey Raoult's law exactly. Real solutions behave ideally only when they are very dilute.

independent variable. Compare with dependent variable.
An independent variable that can be set to a known value in an experiment. Several independent variables may be controlled in an experiment. For example, in an experiment where the vapor pressure of a liquid is measured at several different temperatures, temperature is the independent variable and vapor pressure is the dependent variable.

immiscible. immiscibility. Compare with miscible and partial miscibility.
Two liquids are considered "immiscible" or unmixable if shaking equal volumes of the liquids together results in a meniscus visible between two layers of liquid. If the liquids are completely immiscible, the volumes of the liquid layers are the same as the volumes of liquids orginally added to the mixture.

indicator.
A substance that undergoes an sharp, easily observable change when conditions in its solutions change. See, for example, acid-base indicator and redox indicator.

indicator diagram. PV diagram.
A plot of pressure vs. volume. Lines or curves on the indicator diagram represent processes. The areas under curves on the indicator diagram are equal to the work released by the process.

inductive effect. inductance effect.
An inductive effect is the polarization of a chemical bond caused by the polarization of an adjacent bond. (Field effects are polarization caused by nonadjacent bonds).

inert gas. inert gases; noble gas; noble gases.
Any of the elements of Group 18, which includes helium, neon, argon, krypton, xenon, radon, and element 118. These elements are referred to as "inert" or "noble" because they do not easily form compounds with other elements.

inert pair. inert pair effect.
Valence electrons in an s orbital penetrate to the nucleus better than electrons in p orbitals, and as a result they're more tightly bound to the nucleus and less able to participate in bond formation. A pair of such electrons is called an "inert pair". The inert pair effect explains why common ions of Pb are Pb4+ and Pb2+, and not just Pb4+ as we might expect from the octet rule.

inertia.
The tendency of a body to stay at rest or to continue to move at the same velocity, unless acted on by an outside force. A tractor trailer has more inertia than a bicycle. A bowling ball has more inertia than a tennis ball.

Electromagnetic radiation with wavelength longer than visible light but shorter than that of microwaves. Infrared radiation is produced by hot objects; absorption of infrared radiation causes chemical bonds to vibrate.

infrared spectroscopy. IR spectroscopy.
A technique for determining the structure (and sometimes concentration) of molecules by observing how infrared radiation is absorbed by a sample.

inorganic chemistry.
The study of inorganic compounds, specifically their structure, reactions, catalysis, and mechanism of action.

inorganic compound. inorganic. Compare with organic.
A compound that does not contain carbon chemically bound to hydrogen. Carbonates, bicarbonates, carbides, and carbon oxides are considered inorganic compounds, even though they contain carbon.

insoluble. insolubility. Compare with soluble.
Refers to a substance that does not dissolve in a solvent to any significant degree. Compounds with solubilities of less than 1 g per liter of water are often referred to as 'insoluble', even though they do dissolve to a small extent.

integral enthalpy of solution. (Hsoln) integral heat of solution; integrated heat of solution; integrated enthalpy of solution. Compare with enthalpy of solution.
The heat absorbed or released when a solute is dissolved in a definite amount of solvent. The heat of solution depends on the nature of the solute and on its concentration in the final solution. The integral heat of solution when one mole of solute is added to an infinite amount of solvent is sometimes written as H, soln.

integrated rate law.
Rate laws like d[A]/dt = -k[A] give instantaneous concentration changes. To find the change in concentration over time, the instantaneous changes must by added (integrated) over the desired time interval. The rate law d[A]/dt = -k[A] can be integrated from time zero to time t to obtain the integrated rate law ln([A]/[A]o = -kt, where [A]o is the initial concentration of A.

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.

interference. interfering. Compare with constructive interference and destructive interference.
The amplitudes of waves moving into the same region of space add to produce a single resultant wave. The resultang wave can have higher or lower amplitude than the component waves. See constructive interference and destructive interference.

intermediate. reactive intermediate; reaction intermediate.
A highly reactive substance that forms and then reacts further during the conversion of reactants to products in a chemical reaction. Intermediates never appear as products in the chemical equation for a net chemical reaction.

intermolecular force.
An attraction or repulsion between molecules. Intermolecular forces are much weaker than chemical bonds. Hydrogen bonds, dipole-dipole interactions, and London forces are examples of intermolecular forces.

internal energy. (U, E) Compare with enthalpy and energy.
Internal energy (U) is defined so that changes in internal energy (U) are equal to the heat absorbed or released by a process running at constant volume. While changes in internal energy can be measured using calorimetry, absolute values of internal energy usually cannot be determined. Changes in internal energy are equal to the heat transferred plus the work done for any process.

ion.
An atom or molecule that has acquired a charge by either gaining or losing electrons. An atom or molecule with missing electrons has a net positive charge and is called a cation; one with extra electrons has a net negative charge and is called an anion.

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.

ionic bond. ionically bound; ionic bonding. Compare with covalent bond.
An attraction between ions of opposite charge. Potassium bromide consists of potassium ions (K+) ionically bound to bromide ions (Br-). Unlike covalent bonds, ionic bond formation involves transfer of electrons, and ionic bonding is not directional.

ionic compound. salt. Compare with covalent compound and ionic bond.
A compound made of distinguishable cations and anions, held together by electrostatic forces.

ionic dissociation. ionize; ionization.
When ionic substances dissolve, their ions are surrounded by solvent molecules and separated from each other. This phenomena is also called ionization.

ionic equation. complete ionic equation . Compare with net ionic equation and molecular equation.
An ionic equation is a balanced chemical equation in which strong electrolytes are written as dissociated ions. For example, Ag+(aq) + NO3-(aq) + Na+(aq) + Cl-(aq) = AgCl(s) + Na+(aq) + NO3-(aq) is an ionic equation; AgNO3(aq) + NaCl(aq) = AgCl(s) + NaNO3(aq) is not.

The radii of anions and cations in crystalline ionic compounds, as determined by consistently partitioning the center-to-center distance of ions in those compounds.

ionization energy. (IE,IP) ionization potential. Compare with adiabatic ionization energy, vertical ionization energy, electronegativity, and electron affinity.
The energy needed to remove an electron from a gaseous atom or ion.

isobar. Compare with isotope.
1. A contour line that corresponds to values measured at identical pressures. For example, curves on a plot of gas volumes measured at different temperatures in an open container are isobars. 2. Nuclides that have the same isotopic mass but different atomic number.

isobaric.
Having constant pressure.

isochore.
A contour line that corresponds to values measured at identical volumes. For example, a curve on a plot of gas pressure measured at different temperatures in a rigid container is an isochore.

isochoric.
Having constant volume.

isoelectronic.
Refers to a group of atoms or ions having the same number of electrons. For example, F-, Ne, and Na+ are isoelectronic.

isoleucine. ((CH3)2CHCH(NH2)COOH)
A naturally occuring amino acid with a nonpolar side chain.

isomer. structural isomer.
Molecules with identical molecular formulas but different structural formulas.

isomerization.
A chemical change that involves a rearrangement of atoms and bonds within a molecule, without changing the molecular formula.

isosteric.
Having identical valence electron configurations.

isotherm.
A contour line that corresponds to values measured at identical temperatures. For example, curves on a plot of gas pressure measured at different volumes in a constant temperature bath are isotherms.

isothermal.
Having constant temperature.

isotone. Compare with isotope.
One of a group of atoms or ions with nuclei that contain the same number of neutrons but different numbers of protons.

isotonic. isotonic solution.
Refers to solutions that have equal osmotic pressure.

isotope. isotopic; isotopy. Compare with isomer, allotrope, isobar, and isotone.
Atoms or ions of an element with different numbers of neutronsin their atomic nucleus. Isotopes have the same atomic number but different mass number. Isotopes have very similar chemical properties but sometimes differ greatly in nuclear stability.

isotopic abundance. Compare with natural abundance.
The fraction of atoms of a given isotope in a sample of an element.

isotopic mass. isotopic masses.
The mass of a single atom of a given isotope, usually given in daltons.

IUPAC
International Union of Pure and Applied Chemistry, an organization which sets international standards for chemical nomenclature, atomic weights, and the names of newly discovered elements.

General Chemistry Online! Glossary: I