Chemistry Vocabulary

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Chemistry vocabulary words from Semester One.

absolute zero

the zero point on the Kelvin temperature scale, equivalent to -273.15 degrees C; all molecular motion theoretically stops at this temperature.

accepted value

a quantity used by general agreement of the scientific community.

accuracy

the closeness of a measurement ot the true value of what is being measured.

acid

a compound that produces hydrogen ions in solution, is a hydrogen-ion donor, or an electron-pair acceptor.

acidic solution

any solution in which the hydrogen-ion cncentration is greater thatn the hydroxide-ion concentration.

alkaline solution

a basic solution.

allotrope

one of two or more different molecular forms of an element in the same physical state; oxygen and ozone are allotropes of the element oxygen.

alpha particle

a positively charged particle emitted from certain radioactive nuclei; it consists of two protons and two neutrons and is identical to the nucleus of a helium atom.

anion

any atom or group of atoms with a negative charge.

aqueous solution (aq)

a solution in which the solvent is water.

atom

the smallest particle of an element that retains the properties of that element.

atomic emission spectrum

the pattern of frequencies obtained by passing light emitted by atoms of an elelment in the gaseous state through a prism; the emission spectrum of each element is unique to that element.

atomic mass

the weighted average of the masses of the isotopes of an element.

atomic mass unit (amu)

a unit of mass equal to one-twelfth the mass of carbon-12 atom.

atomic number

the number of protons in the nucleus of an atom of an element.

atomic orbital

a region in space around the nucleus of an atom where there is a high probability of finding an electron.

Aufbau principle

electrons enter orbitals of lowest energy.

Avogadro's hypothesis

equal volumes of gases at the same temperature and pressure contain equal numbers of particles.

Avogadro's number

the number of representative particles contail in one mole of a substance; equal to 6.02 X 10^23 particles.

balanced equation

a chemical equation in which mass is conserved; each side of the equation has the same number of atoms of each element.

basic solution

any solution in which the hydroxide-ion concentration is greater than the hydrogen-ion concentration.

beta particle

a fast-moving eleron emitted from certain radioactive nuclei; it is formed whn a neutron decomposes into a proton and an electron.

beta radiation

fast-moving electrons (beta particles) emitted from a radioactive source.

binary compound

a compound composed of two elements; NaCl and Al2O3 are binary compounds.

catalyst

a substance that increases the rate of reaction by lowering the activation-energy barrier; the catalyst is not used up.

cathode

the electrode at which reduction occurs.

cathode ray

a stream of electrons produced at the negative electrode (cathode) of a tube containing a gas at low pressure.

cation

any atom or group of atoms with a positive charge.

Celsius scale

the temperature scale on which the freezing point of water is 0 degrees Celcius, and the boiling point is 100 degrees Celcius.

chemical equation

an expression representing a chemical reaction; the formulas of the reactants (on the left) are connected by an arrow with the formulas for the products (on the right)

chemical equalibirium

a state of balance in which forward and reverse reactions are taking place at the same rate; no net change in the amounts of reactants and products occurs in the chemical system.

chemical formula

shows the number and type of atoms present in the smallest representative unit of a substance; the chemical formula of ammonia, with one nitrogen and three hydrogens, in NH3.

chemical property

the ability of a substance to undergo chemicl reactions and to form new substances.

chemical reaction

the changing of substances to other substances by breaking of bonds in reactants and the formation of bonds in products.

chemical symbol

a one or two letter representation of an element.

chemistry

the study of the structure, properties, and composition of substances, and the changes that susbtances undergo.

colloid

a mixture who particles are intermediate in size between those of a suspension and a solute solution.

combination reaction

a chemical change in which two or more substances react to form a single new substance; also called a synthesis reaction.

combustion reaction

a chemical change in which oxygen reacts with another substance, often producing energy in the form of heat and light.

compound

a substance that can be separated into simpler substances (elements or other compounds) only by chemical reactions.

compressibility

a measure of how much the volume of matter decreases under pressure.

concentrated solution

a solution containing a large amount of solute.

concentration

a measurement of the amount of solute that is dissolved in a given quantity of solvent; usually expressed as mol/L.

condensed structural formula

a structural formula that leaves out some bonds and/or atoms the presence of these atoms or bond is understood.

conversion factor

a ration of equivalent measurements used to convert a quantity from one unit to another.

coordinate covalent bond

a covalent bond formed when one atom contributes both bonding electrons.

Dalton's atomic theory

the first theory to relate chemical changes to events at the atomic level.

de Broglie's equation

an equation that describes the wavelength of a moving particle; it predicts that all matter exhibits wavelike motions.

decomposition reaction

a chemical change in which a single compound is broken down into two or more simpler products.

density

the ration of the mass of an object to its volume.

diffusion

the tendency of molecules and ions to move toward areas of lower concentration until the concentration is uniform throughout the system.

dimensional analysis

a technique of problem-solving that uses the units that are part of a measurement to help solve the problem.

double covalent bond

a covalent bond in which two pairs electrons are shared by two atoms.

double-replacement reaction

a chemical change involves an exchange of positive ions between two compounds.

electrode

a conductor in a circuit that carries electrons to or from a substance other than metal.

electron

a negatively charged subatomic particle.

electron configuration

the arrangement of electrons around the nucleus of an atom in its ground state.

element

a substance that cannot be changed into simpler substances under normal laboratory conditions.

elementary reaction

a reactioni in which reactants are converted to products in a single step.

empirical formula

a formula with the lowest whole-number ration of elements in a compound; the empirical formula of hydrogen peroxide (H2O) is HO.

energy

the capacity for doing work; it exists in several forms, including chemical, nuclear, electical, rdiant, mechanical, and thermal energies.

energy level

a region around the nucleus of an atom where an electron is likely to moving.

error

the difference between the accepted value and the experimental value.

experiement

a carefully controlled, repeatable procedure for gathering data to test a hypothesis.

experimental value

a quantitative value measured during an experiement.

formula unit

the lowest whole-number ration of ions in an inic compound; in magnesium chloride, the ration of magnesium ions to chloride ions is 1:2 and the formula unit is MgCl2.

frequency

the number of wave cycles that pass a given point perunit of time; there is an inverse relationship between the frequency and the wavelength.

gamma radiation

high energy electromagnetic radiation emitted by certain radioactive nuclei; gamma rays have no mass or electrical charge.

gas

matter that has no definite shape or volume; it adopts the shape and volume of its container.

gram

a metric mass unit equal to the mass of 1 cm cubed of water at 4 degrees Celcius.

gram atomic mass (gam)

the mass, in grams, of one mole of atoms in a monoatomic element; it is numberically equal to the atomic mass in amu.

gram formula mass

the mass of one mole of an ionic compound.

gram molecular mass

the mass, in grams, of one mole of a molecular substance.

group

a vertical colum of elements in the periodic table; the constituent elements of a group have similar chemical and physical properties.

halogen

any memeber of the nonmeallic elements in Group 7A of the periodic table.

heat

the energy that is transferred from one body to another because of a temperature difference.

Hertz (hz)

the SI unit of frequency, equal to one cycle per second.

heterogeneous mixture

a mixture that is not uniform in compositionl its componenets are not readily distinguished.

homogeneous mixture

a mixture that is completely uniform in composition; its components are not readily distinguished.

Hund's rule

when electrons occupy orbitals of equal energy, one electron enters each orbital until all orbitals contain one electron with their spins parallel.

hydrocarbon

an organic compound that contains only carbon and hydrogen.

hydrogen bond

a relatively strong intermolecular force in which a hydrogen atom that is covalently bonded to very electronegative atom is also weakly bonded to an unshared electron pair of another electronegative atom in the same molecule or one nearby.

hypothesis

a proosed explanation for observations.

intermediate

a product o a reaction that immediately becomes a reactant of another reaction.

International System of Units (SI)

the revised version of the metric system, adopted by international agreement in 1960.

ion

an atom or group of atoms that has a positive or negative charge; cations are ions with a positive charge, and anions are ions with a negative charge.

ionic bond

the electrostatic attraction that binds oppositely charged ions together.

ionic compound

a compound composed of positive and negative ions.

isotopes

atoms of the same element that have the same atomic bumber but different atomic masses due to a different number of neutrons.

joule (j)

the SI unit of energy; 4.184 J equal one calorie.

Kelvin scale

the temperature scale in which the freezing point of water is 273 K and the boiling point is 373 K; 0 K is absolute zero.

kilogram

he mass of 1 L of water at 4 degrees C; it is the base unit of mass in SI.

law of conservation of energy

energy that is neither created nor destroyed in an ordinary chemical or physical process.

law of conservation of mass

mass can be neither created nor destroyed in an ordinary chemical or physical process.

law of definite proportions

in any sample of a chemical compound, the elements are always combined in the same proportion by mass.

liquid

a form of matter that flows, has a fixed volume, and takes the shape of its container.

liter (L)

the volume of a cube measuring 10 centimeters on each edge (1000 cm cubed); it is the common unprefixed unit of volume in the metric system.

mass

the amount of matter than an object contains; the SI base unit of mass is the kilogram.

mass number

the total number of protons and neutrons in the nucleus of an atom.

matter

anything that takes up space and has mass.

melting point

the temperature at which a substance changes from solid to a liquid; the melting point of water is 0 degrees Celcius.

metal

one of a class of elements that includes a large majority of the known elements; metals are characteristically lustrous, malleable, ductile, and good conductors of heat and electricity.

metallic bond

the force of attraction that holds metals together; it consists of the attraction of free-floating valence elecrons for positively charged metal ions.

metalloid

one of a class of elements having properties intermediate to metals and nonmetals.

meter (m)

the base unit in length in SI.

mixture

a physical blend of two or more substances that are not chemically combined.

molar mass

a general expression used to refer to the mass of a mole of any substance unless a more specific term is needed to avoid confusion.

molar volume

the volume occupied by 1 mole of gas a standard temperature and pressue (STP); 22.4 L

mole (mol)

the amount of a substance that contains 6.02 X 10^23 representative particles of that substance.

molecular compound

a compound that is composed of molecules.

molecular formula

a chemical formula that shows the actual number and kinds of atoms present in a molecule of a compound.

molecular orbital

an orbital resulting from the overlapping of atomic orbitals when two atoms combine.

molecule

a neutral chemically bonded group of atoms that act as a unit.

net ionic equation

an equation for a reaction in solution showing only those particles that are directly involved in the chemical change.

neutron

a subatomic particle with no charge and a mass of 1 amu; found in the nucleus of the atom.

noble gas

any member of a group of gaseous elements in Group 0 of the periodic table; the s and p sublevels of their outermost energy level are filled.

nonmetal

one of a class of elements that are not lustrous and are generally poor conductors or heat and electricity; non-metals are grouped on the right side of the periodic table.

nucleus

the dense central porportion of an atom, composed of protons and neutrons.

observation

information obtained through the senses; observation in science often involves a measurement.

organic chemistry

the study of compounds that contain the element carbon.

oxidation

a process that involves complete or partical loss of electrons or a gain of oxygen; it results in an increase of the oxidation number of an atom.

partial pressure

the pressure exerted by each gas in a gaseous mixture.

pascal

the SI unit of pressure.

Pauli exclusion principle

no more than two electrons can ocupy an atomic orbital; these elctrons must have opposite spins.

percent composition

the percent by mass of each element in a compound.

percent error

the percent that a measured value differes from the accepted value

percent yeild

the ratio of the actual yield to the theoretical yield for a chemical reaction expressed as a percentage; a measure of the efficiency of a reaction.

period

a horizontal row of elements in the period table.

periodic law

when the elements are arranged in order of increasing atomic number, there is a period repition of their physical and chemical properities.

periodic table

an arrangelment of elements into row and columns according to similarities in their properties.

pH

a number used to denote the hydrogen-ion concetraion, or acidity, of a solution it is the negative logarithm of the hydgrogen-ion concetration of a solution.

phase

any part of a system with uniform composition and properties.

photoelectric effect

electrons are ejected by certain metals when they absorb light with a frequency above a threshold frequency.

photon

a quantum of light; a descrete bundle of electromagnetic energy that behaves as a particle.

physical change

an alteration of a substance that does not affect its chemical composition.

physical property

a quality of a substance that can be observed or measured without changing the substance's chemical composition.

Planck's constant (h)

a number used to calculate the radiant energy (E) absorbed or emitted by a body based on the frequency of radiation.

polar bond

a bond formed when two different atoms are joined by a covalent bond and the bonding electrons are shared unequally.

polar molecule

a molecule, like water, in which one or more atoms is slightly negative and one or more is slightly positive, unless molecular geometry causes the polarieis to cancel each other out.

polyatomic ion

a tighly bound group of atoms that behaves as a unit and carries a charge.

product

a substance formed in a chemical reaction

proton

a positively charged subatomic particle found in the nucleus of an atom.

qualitative measurement

a measurement that gives descriptive, nonnumeric results.

quantitative measurements

a measurement that gives definite, ususally numeric results.

quantum

the amount of energy needed to move an electron from its present energy level to the next higher one.

quantum mechanical model

the modern description, primarily mathematical, of the behavior of electrons in atoms.

radioactive decay

the spontaneous emission of radiation by an unstable nucleus; the rate of decay is unafected by temperature, pressure, or catalyst.

radioactivity

the processes by which unstable atomic nuclei achieve stability.

radioisotope

an isotope that has an unstable nucleus and undergoes radioactive decay.

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