A
absolute zero -- the temperature at which the volume of an ideal gas becomes zero. The theoretical coldest temperature that can be approached but never reached. Absolute zero is zero on the Kelvin scale, -273.15C on the Celsius scale, and -459.67F on the Fahrenheit scale.
acceleration -- the change in velocity over time. Acceleration due to gravity is given as the gravitational constant (9.8 m/s 2 ).
acid-- a compound that gives off H + ions in solution.
acidic -- used to describe a solution with a high concentration of H + ions.
activation energy -- the minimum energy required to convert reactants into products.
adhesion -- an attraction between different substances.
alkali metal -- The Group 1 elements, lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr).
alkaline -- having a pH greater than 7.
alkaline earth metal -- the Group 2 elements, beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).
alloy -- a mixture containing mostly metals. For example, brass is an alloy of copper and zinc. Steel contains iron and other metals, but also carbon.
amplitude -- the displacement of a wave from zero. The amplitude for a wave is the height of a peak or the depth of a trough.
anion -- an ion with a negative charge
anode -- an electrode where electrons are lost (oxidized) in redox reactions.
area -- a surface measurement determined by multiplying length by width.
associative property -- a property in math which states that: (A+B) +C=A+ (B+C) and (A*B)*C=A*(B*C)
atmosphere (atm) -- a unit of pressure, equal to a barometer reading of 760 mm Hg. 1 atmosphere is 101325 pascals and 1.01325 bar.
atom -- the smallest object that retains properties of an element.
atomic number -- the number of protons in an element.
Avogadro's law -- equal volumes of an ideal gas contain equal numbers of molecules, if both volumes are at the same temperature and pressure.
Avogadro's number -- a number representing the number of molecules in one (1) mole: 6.023 * 10 23 .
B
bar -- a unit of pressure. 1 bar = 10 5 pascals = 1.01325 atmospheres.
base -- a substance which gives off hydroxide ions ( OH - ) in solution.
basic -- a substance having the characteristics of a base.
boiling point -- the temperature at which the internal pressure of a liquid is equal to the external pressure being applied to it.
Boyle's Law -- under conditions of constant temperature and quantity, there is an inverse relationship between the volume and pressure for an ideal gas. For example, as the pressure increases, the volume decreases. P 1 V 1 = P 2 V 2
brittleness -- the extent to which a substance will shatter.
buffer solutions -- a solution that resists change in its pH, even when small amounts of acid or base are added.
C
calorie -- the amount of heat required to raise the temperature of 1 g of water 1°C. One calorie is equivalent to exactly 4.184 J.
catalyst -- any substance that speeds up a chemical process without actually changing the products of reaction
cathode -- an electrode where electrons are gained (reduction) in redox reactions.
cations -- an ion with a positive charge.
charge -- describes an object's ability to repel or attract other objects. Protons have positive charges while electrons have negative charges. Like charges repel each other while opposite charges, such as protons and electrons, attract one another.
Charles' Law -- the volume of a quantity of gas, held at constant pressure, varies directly with the Kelvin temperature. For example, as the temperature increases, the volume increases. V 1 /T 1 = V 2 /T 2
chemical change -- a change that produces two or more different kinds of matter that were not present before the change.
chemical equation -- an expression of a fundamental change in the chemical substances.
cohesion -- an attraction between like molecules.
combustion -- when substances combine with oxygen and release energy.
commutative property -- a math property which states: A+B=B+A and A*B=B*A
compound -- two or more atoms chemically combined by covalent or ionic bonds.
concentration -- the amount of substance in a specified space.
condensation -- the temperature at which a substance changes from a gas to a liquid.
conjugate acid -- a substance which can lose a H + ion to form a base.
conjugate base -- a substance which can gain a H + ion to form an acid.
corrosion -- a reaction that involves action of an oxidizing agent on a metal. Rust is an example of corrosion.
covalent bond -- when two atoms share at least one pair of electrons.
D
Dalton's law of partial pressure -- the total pressure exerted by a mixture of gases is the sum of the pressures that each gas would exert if it were alone.
decay -- the change of an element into a different element, usually with some other particle(s) and energy emitted.
density -- the mass per unit volume of a substance. D= m/V
density property -- a math property which states that between any two real numbers, there is always another real number. For example, between 5.61 and 5.62, there is 5.611.
diffraction -- the ability of a wave to bend around the edges of obstacles or holes.
dilution -- adding solvent to a solution to lower its concentration.
dissociation -- breaking down of a compound into its components.
distributive property -- a math property which states: A*(B+C) = (A*B) + (A*C)
double bond -- when an atom is bonded to another atom by two sets of electron pairs.
ductility -- the ability to be drawn into thin wire.
E
effusion -- the movement of gas molecules through a small opening.
elasticity -- the ability to stretch out and then snap back into place.
electrode -- a device that moves electrons into or out of a solution by conduction.
electrolysis -- changing the chemical structure of a compound using electrical energy.
electromagnetic spectrum -- the complete range of wavelengths which light can have, including: infrared, ultraviolet, and all other types of electromagnetic radiation, as well as visible light.
electron -- a particle found in an atom that has a negative charge.
electron geometry -- the structure of a compound based on the arrangement of its electrons.
electronegativity -- a measure of a substance's ability to attract electrons.
electrostatic forces -- the attractive or repulsive forces between charged objects.
element -- the simplest pure form of a substance.
empirical formula -- a formula showing the simplest ratio of elements in a compound.
endothermic -- a reaction that absorbs heat.
energy -- the ability to do work.
enthalpy -- a change in heat.
entropy -- a measure of energy dispersal.
equilibrium -- when the reactants and products are in a constant ratio.
evaporation -- the change of a liquid into a gas.
exothermic -- a reaction that gives off.
exponentiation -- raising something to a power.
F
family -- the vertical columns on the periodic table.
force -- any action between two bodies which changes their relative position in space . Newton's Second Law of Motion states: force = mass * acceleration.
free electron -- an electron which is not attached to a nucleus.
freezing point -- the temperature at which a liquid becomes a solid
frequency -- the number of events in a given unit of time.
G
gas -- matter in a form that has low density, is easily compressible and expandable, and expands spontaneously when placed in a larger container. No definite shape or volume.
geiger counter -- an instrument that measures radiation output.
H
half-life -- the amount of time it takes for half an initial amount to disintegrate.
halogen -- the group 7 elements, fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). The name means "salt former"; halogens react with metals to form binary ionic compounds.
Heisenberg Uncertainty principle -- the principle states that it is not possible to know a particle's location and momentum precisely at any time.
I
Ideal Gas Law -- describes the relationship between pressure (P), temperature (T), volume (V), and moles of gas (n). PV=nrT
identity property -- a math property which states: A+0=A and A*1=A.
inert gas -- any of the elements of Group 18, which includes helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), radon (Rn) and the undiscovered element 118. These elements are referred to as "inert" or "noble" because they do not easily form compounds with other elements.
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.
infrared radiation -- Electromagnetic radiation with wavelength longer than visible light but shorter than that of microwaves.
inorganic compound -- a compound that does not contain carbon chemically bound to hydrogen.
insoluble -- refers to a substance that does not dissolve in a solvent to any significant degree.
intermolecular forces -- the forces between molecules.
intramolecular forces -- the forces within molecules.
inverse -- a math property which states: A+ (-A) =0 and A*(1/A) =1
ion -- a charged atom that has had electrons added or removed.
ionic bonds -- when two oppositely charged atoms share at least one pair of electrons but the electrons spend more time near one of the atoms than the other.
ionization energy -- the energy required to remove an electron from a specific atom.
ionizes -- when a substance breaks into its ionic components.
isotope -- any form of an element with the same number of protons but a different number of neutrons, and thus different masses.
J
joule (J) -- the SI unit of energy, equal to the work required to move a 1 kg mass against an opposing force of 1 newton. 1 J = 1 kg m 2 s -2 = 4.184 calories.
K
Kelvin -- the SI Unit of temperature. It is the degrees Celsius plus 273.
kinetic energy -- the energy an object has because of its mass and velocity. Kinetic Energy=0.5* mass*velocity 2 .
L
law of conservation of mass -- there is no change in total mass during a chemical change.
Le Chatlier's principle -- states that a system at equilibrium will oppose any change in the equilibrium conditions.
Lewis structures -- a way of representing molecular structures by their valence electrons.
limiting reagant -- the reactant that will be exhausted first.
liquid -- a state of matter that has a high density, is incompressible compared to a gas and takes the shape of whatever it is contained in. Definite volume, but no definite shape.
M
malleability -- the ability to be hammered into thin sheets. For example, gold is very malleable.
mass -- the measure of the amount of matter in an object.
mass number -- the number of protons and neutrons in an atom.
matter -- anything that has mass.
metal -- 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.
metalloid -- an element with both metallic and nonmetallic properties. Examples are silicon, arsenic, and germanium.
mixture -- two or more substances physically, but not chemically, combined.
molality -- the number of moles of solute per kilogram of solvent.
molar -- an term expressing molarity, the number of moles of solute/ liters of solution.
molarity -- the number of moles of solute per liter of solution.
mole -- a collection of 6.023* 10 23 number of objects.
molecular formula -- a formula that shows the number of atoms of each element present in a molecule.
molecular geometry -- the shape of a molecule based on the relative positions of the atoms.
molecular weight -- the combined weight of all the elements in a compound.
molecule -- two or more atoms chemically combined.
momentum -- a property that measures the tendency of a moving object to keep moving in the same direction.
N
natural gas -- a mixture of methane and other gases, found trapped over petroleum deposits under the earth.
neutral -- the lack of an electrical charge (positive or negative).
neutron -- a particle, with no electrical charge, found in the nucleus of an atom.
non-metal -- a nonmetal is a substance that conducts heat and electricity poorly, is brittle, waxy or gaseous, and cannot be hammered into sheets or drawn into wire.
nuclear fission -- the splitting of a nucleus into two smaller nuclei and neutrons. The smaller nuclei have higher binding energy than the original nucleus, and fission results in the release of energy.
nuclear fusion -- the combination of two smaller nuclei to form a larger nucleus. The larger nucleus has higher binding energy per nucleon than the original nuclei, and fusion results in the release of energy.
nucleus -- the central part of an atom that contains the protons and neutrons.
O
Octet Rule -- a rule applied to Lewis structures that states atoms tend to gain, lose or share electrons with other atoms in a molecule until they hold or share eight valence electrons.
orbital -- an energy state in the atomic model which describes where an electron will likely be.
organic -- compounds that contain carbon chemically bound to hydrogen.
oxidation-reaction -- a reaction where a substance loses electrons
oxidation-reduction-reaction -- a reaction involving the transfer of electrons.
P
parent isotope -- an element that undergoes nuclear decay.
partial pressures -- the pressure exerted by a certain gas in a mixture.
particle -- an individual portion of matter.
particulate -- composed of distinct particles. Smoke is particulate; pure gases are not.
periodic table -- grouping of the known elements by their number of protons developed by Russian chemist Dmitri Mendeleev.
pascal (Pa) -- the SI unit of pressure, equal to a force of one newton per square meter. 101325 pascals = 1 atmosphere; 10 5 pascals = 1 bar.
period -- the horizontal rows of the periodic table.
pH -- a measurement of the concentration of the hydrogen ions in a substance (acidity) of a solution.
photons -- a packet of energy, which behaves like both a wave and a particle.
physical change -- a change which does not alter the chemistry of the substance.
physical property -- a property that can be measured without changing the chemical composition of a substance.
plasma -- 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.
polar molecule -- a molecule with a partial charge.
potential energy -- the energy an object has because of its composition or position.
power-- the rate at which energy is supplied.
pressure -- the force per unit area.
products -- the compounds that are formed when a reaction is complete.
proportion -- an equality between two ratios.
proton -- the positively charged particle found in the nucleus of an atom.
Q
quantum -- something which comes in discrete units. For example, money is quantized (divided into units); it comes in quanta (divisions) of one cent.
quantum numbers -- a set of numbers used to describe an electron's position.
R
radian -- an angle with vertex at the center of a circle of radius r that encompasses an arc of length r.
radiant energy -- energy which is transmitted away from its source. For example, energy that is emitted when electrons transition down from one level to another.
radiant intensity -- energy of radiation striking a unit area per unit time. The SI unit of radiant power is J m -2 s -1 .
radiation -- energy in the form of photons.
radioactive -- a substance containing an element which decays.
rare earth element -- a metallic element that belongs to Group 3B or to the lanthanide series.
ratio -- two quantities expressed as the quotient of one divided by the other; the ratio of a to b is written as a:b or a/b.
reactants -- the substances initially present in a chemical reaction.
redox reaction -- a reaction that involves transfer of electrons from one substance to another.
reduction reaction -- a reaction in which a substance gains at least one electron.
S
salts -- ionic compounds that can be formed by replacing one or more of the hydrogen ions of an acid with another positive ion.
scientific notation -- a system for reporting very small or very large numbers by writing the number as a decimal number between 1 and 10, multiplied by a power of 10. For example, 602000000000000000000000 is written in scientific notation as 6.02 x 10 23 . 0.000323 is written in scientific notation as 3.23 x 10 -4 .
shells -- where the electrons generally stay. There are 4 types of electron shells: s, p, d and f shells.
single bond -- when an electron pair is shared by two different elements.
SI unit -- a unit of measurement established by the Systeme International d'Unites.
solid -- a substance that is held in a fixed form by cohesion among its particles. A definite shape and definite volume.
soluble -- c apable of being dissolved in a solvent.
solute -- the substance dissolved in a solution.
solution -- a mixture of a solid and a liquid where the solid never settles out.
solvent -- the liquid in which something is dissolved.
specific gravity -- the mass of a unit volume of a substance relative to the mass of a unit volume of water. Water has a specific gravity of 1.00000 g/mL.
specific heat -- the amount of heat it takes for a substance to be raised one degree C.
spontaneous reaction -- a reaction that will proceed without any outside energy.
states of matter -- solid, liquid, gas and plasma.
STP -- an abbreviation for standard temperature and pressure. This is 0 o C and 1 atm.
sublimation -- c onversion of a solid directly into a gas, without first melting into a liquid.
substance -- any particular kind of matter.
surface tension -- the work required to expand the surface of a liquid by unit area.
synthetic -- a complex product manufactured from simpler reactants.
T
temperature -- a measure of the hotness or coldness of an object. It determines the direction of spontaneous heat flow (always from hot to cold).
term -- each compound or element in a chemical equation.
thermal energy -- the energy an object possesses by virtue of its temperature.
thermodynamics -- the study of heat and energy flow in chemical reactions.
titration -- reacting a solution of unknown concentration with a solution of a known concentration for the purpose of finding out more about the unknown solution.
torr -- a unit of pressure defined so that 760 Torr is exactly 1 atmosphere. A Torr is equivalent to 1 mm Hg on barometer readings taken at 0°C.
toxicology -- the study of poisons, including identification, isolation, biological effects, mechanism of action, and development of antidotes.
transition metal -- an element with an incomplete d subshell.
U
ultraviolet light -- electromagnetic radiation with wavelength longer than that of x-rays, but shorter than that of visible light.
unit -- a standard for comparison in measurements.
V
vacuum -- a volume which contains no matter.
valence electrons -- the electrons in the outermost shell of an atom.
van der Waals equation -- an equation for non-ideal gases that accounts for intermolecular attraction and the volumes occupied by the gas molecules.
velocity -- speed of an object.
viscosity -- the resistance a liquid exhibits to flow.
visible light -- electromagnetic radiation with a wavelength between 400 and 750 nm.
volatile -- a solid or liquid material that easily vaporizes.
volume -- the amount of space a substance occupies.
W
wave -- a signal which propagates through space, much like a water wave moves through water.
wavelength -- the length between two consecutive troughs (low points) or peaks (high points) of a wave.
weak acid -- a substance capable of donating hydrogen but does not completely ionize in solution.
weak bases -- a substance capable of accepting hydrogen but do not completely ionize in solution.
weight -- the force exerted by an object in a gravitational field. The weight (W) of an object arises from its mass: (W = mg) where g is the acceleration due to gravity (about 9.8 m/s 2 on Earth).
work-- an expression of the movement of an object against some force.
X
x-ray -- a very high energy form of electromagnetic radiation.
Y
yield -- the amount of product actually obtained in a chemical reaction.