chem dictionary1

7/27/2019 Chem Dictionary1

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A

AccelerationMeasure of how fast velocity is changing, so we canthink of it as the change in velocity over change intime. The most common use of acceleration is

acceleration due to gravity, which can also appear asthe gravitational constant (9.8 m/s2).

AcidCompound that gives off H+ ions in solution.

AcidicDescribes a solution with a high concentration ofH+ ions.

AnionIons with a negative charge.

AnodeThe electrode where electrons are lost (oxidized) inredox reactions.

AreaMeasures the size of a surface using lengthmeasurements in two dimensions.

AssociativityA property in math which states that: (A+B)+C=A+(B+C) and (A*B)*C=A*(B*C).

Atmospheres

Common units for measuring pressure.

AtomThe smallest object that retains properties of anelement. Composed of electrons and a nucleus(containing protons and neutrons).

Atomic numberNumber of protons in an element.

Avogadro's number

Number representing the number of molecules in one(1) mole: 6.022 * 1023.

B

BaseSubstance which gives off hydroxide ions (OH-) insolution.

BasicHaving the characteristics of a base.

Bohr's atomBohr made significant contributions to the atom. Heunderstood the line spectra-- the reason why onlycertain wavelengths are emitted when atoms jumpdown levels.

Buffer solutionsSolutions that resist changes in their pH, even whensmall amounts of acid or base are added.

C

CatalystSubstance that speeds up a chemical process withoutactually changing the products of reaction.

CathodeElectrode where electrons are gained (reduction) inredox reactions.

CationsIon with a positive charge.

Central atomIn a Lewis structure, usually the atom that is the leastelectronegative.

ChargeDescribes an object's ability to repel or attract otherobjects. Protons have positive charges while electronshave negative charges. Like charges repel each other


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while opposite charges, such as protons and electrons,attract one another.

Chemical changesProcesses or events that have altered the fundamentalstructure of something.

Chemical equationAn expression of a fundamental change in the chemicalsubstances.

ClosureA mathematical term which says that if you operatedon any two real numbers A and B with +, -, * or /, youget a real number.

Colligative propertiesProperties of a solution that depend only on thenumber of particles dissolved in it, not the properties of

the particles themselves. The main colligativeproperties addressed at this web site are boiling pointelevation and freezing point depression.

CombustionWhen substances combine with oxygen and releaseenergy.

CommutativityA math property which states: A+B=B+A andA*B=B*A.

Compound

Two or more atoms joined together chemically, withcovalent or ionic bonds.

ConcentrationThe amount of substance in a specified space.

Conjugate acidA substance which can lose an H+ ion to form a base.

Conjugate baseA substance which can gain an H+ ion to form an acid.

Covalent bondsWhen two atoms share at least one pair of electrons.

D

Daughter isotopeIn a nuclear equation the compound remaining afterthe parent isotope (the original isotope) has undergonedecay. A compound undergoing decay, such as alphadecay, will break into an alpha particle and a daughterisotope.

DecayChange of an element into a different element, usuallywith some other particle(s) and energy emitted.

DecimalThe number of digits to the right of the decimal point in

a number.

DenseA compact substance or a substance with a highdensity.

DensityMass per unit volume of a substance.

Dipole-dipole forcesIntermolecular forces that exist between polarmolecules. Active only when the molecules are closetogether. The strengths of intermolecular attractionsincrease when polarity increases.

Dispersion forces (also called London dispersionforces)Dispersion is an intermolecular attraction force thatexists between all molecules. These forces are theresult of the movement of electrons which cause slightpolar moments. Dispersion forces are generally veryweak but as the molecular mass increases so doestheir strength.

Dissociation


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Breaking down of a compound into its components toform ions from an ionic substance.

DistributivityA math property which states: A*(B+C)=(A*B)+(A*C).

Double bondWhen an atom is bonded to another atom by two setsof electron pairs.

E

EffusionMovement of gas molecules through a small opening.

Electrochemical cell

Gives an electric current with a steady voltage as aresult of an electron transfer reaction.

ElectrodesDevice that moves electrons into or out of a solution byconduction.

ElectrolysisChanging the chemical structure of a compound usingelectrical energy.

Electromagnetic spectrumComplete range of wavelengths which light can have.

These include infrared, ultraviolet, and all other typesof electromagnetic radiation, as well as visible light.

ElectronOne of the parts of the atom having a negative charge.Indivisible particle with a charge of -1.

Electron geometryStructure of a compound based on the arrangement ofits electrons.

Electronegativity

Measure of a substance's ability to attract electrons.

Electrostatic forcesForces between charged objects.

Element

Substance consisting of only one type of atom.

Empirical formulaFormula showing the simplest ratio of elements in acompound.

EndothermicProcess that absorbs heat from its surroundings as thereaction proceeds.

EnergyAbility to do work.

EnthalpyChange in heat at constant pressure.

EntropyMeasure of the disorder of a system.

EquilibriumWhen the reactants and products are in a constantratio. The forward reaction and the reverse reactionsoccur at the same rate when a system is in equilibrium.

Equilibrium constantValue that expresses how far the reaction proceeds

before reaching equilibrium. A small number meansthat the equilibrium is towards the reactants side whilea large number means that the equilibrium is towardsthe products side.

Equilibrium expressionsThe expression giving the ratio between the productsand reactants. The equilibrium expression is equal tothe concentration of each product raised to itscoefficient in a balanced chemical equation andmultiplied together, divided by the concentration of theproduct of reactants to the power of their coefficients.


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Equivalence pointOccurs when the moles of acid equal the moles of basein a solution.

Exothermic

Process that gives off heat to the environment.

ExponentiationRaising something to a power.

F

ForceAn entity that when applied to a mass causes it toaccelerate. Sir Isaac Newton's Second Law of Motionstates: the magnitude of a force=mass*acceleration.

Free electronElectron which is not attached to a nucleus.

FrequencyNumber of events in a given unit of time. Whendescribing a moving wave, means the number of peakswhich would pass a stationary point in a given amountof time.

G

Geiger counter

Instrument that measures radiation output.

Gibb's free energyThe energy of a system that is available to do work atconstant temperature and pressure.

Graham's lawThe rate of diffusion of a gas is inversely proportionalto the square root of its molar mass.

H

Half lifeThe amount of time it takes for half an initial amount todisintegrate.

Heisenberg uncertainty principleThis principle states that it is not possible to know aparticle's location and momentum preciselyat anytime.

Hydrogen bondingStrong type of intermolecular dipole-dipole attraction.Occurs between hydrogen and F, O or N.

HydrolysisThe reactions of cations with water to produce a weakbase or of anions to produce a weak acid.

I

Ideal gas lawPV=nRTDescribes the relationship between pressure (P),temperature (T), volume (V), and moles of gas (n). Thisequation expresses behavior approached by real gasesat low pressure and high temperature.

IdentityA math property which states: A+0=A and A*1=A.

Intermolecular forcesForces between molecules.

Intramolecular forcesForces within molecules. Forces caused by theattraction and repulsion of charged particles.

InverseA math property which states: A+(-A)=0 and A*(1/A)=1

Ion


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Removing or adding electrons to an atom creates anion (a charged object very similar to an atom).

Ion-dipole forcesIntermolecular force that exists between chargedparticles and partially charged molecules.

Ionic bondsWhen two oppositely charged atoms share at least onepair of electrons but the electrons spend more timenear one of the atoms than the other.

Ionization energyEnergy required to remove an electron from a specificatom.

IonizesWhen a substance breaks into its ionic components.

IsotopesElements with the same number of protons but havedifferent numbers of neutrons, and thus differentmasses.

K

KelvinThe SI Unit of temperature. It is the temperature indegrees Celsius plus 273.15.

Kinetic energyEnergy an object has because of its mass and velocity.Objects that not moving have no kinetic energy.(Kinetic Energy=0.5* mass*velocity2.

L

Le Chatlier's principleStates that a system at equilibrium will oppose anychange in the equilibrium conditions.

Lewis structuresA way of representing molecular structures based onvalence electrons.

Limiting reagent

The reactant that will be exhausted first.

Line spectraSpectra generated by excited substances. Consists ofradiation with only specific wavelengths.

M

Mass numberThe number of protons and neutrons in an atom.

MixtureComposed of two or more substances, but each keepsits original properties.

MolalityThe number of moles of solute (the material dissolved)per kilogram of solvent (what the solute is dissolvedin).

MolarA term expressing molarity, the number of moles ofsolute per liters of solution.

MolarityThe number of moles of solute (the material dissolved)per liter of solution. Used to express the concentrationof a solution.

MoleA collection of 6.022* 1023 numbers of objects. Usuallyused to mean molecules.

Molecular formula


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Shows the number of atoms of each element present ina molecule.

Molecular geometryShape of a molecule, based on the relative positions ofthe atoms.

Molecular massThe combined mass (as given on the periodic table) ofall the elements in a compound.

MoleculeTwo or more atoms chemically combined.

Mole fractionThe number of moles of a particular substanceexpressed as a fraction of the total number of moles.

N

NeutralAn object that does not have a positive or negativecharge.

NeutronA particle found in the nucleus of an atom. It is almostidentical in mass to a proton, but carries no electriccharge.

NmAn abbreviation for nanometers. A nanometer is equalto 10-9 meters.

NucleusThe central part of an atom that contains the protonsand neutrons. Plural nuclei.

O

Octet

In Lewis structures the goal is to make almost allatoms have an octet. This means that they will haveaccess to 8 electrons regularly, even if they do have toshare some of them.

Orbitals

An energy state in the atomic model which describeswhere an electron will likely be.

Oxidation numberA number assigned to each atom to help keep track ofthe electrons during a redox-reaction.

Oxidation reactionA reaction where a substance loses electrons.

Oxidation-reduction-reactionA reaction involving the transfer of electrons.

OxoacidWhen one or more hydroxide (OH) groups are bondedto a central atom.

P

Parent isotopeAn element that undergoes nuclear decay.

Partial pressure

The pressure exerted by a certain gas in a mixture.

ParticleSmall portion of matter.

Percent compositionExpresses the mass ratio between different elementsin a compound.

Periodic tableGrouping of the known elements by their number ofprotons. There are many other trends such as size of


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elements and electronegativity that are easilyexpressed in terms of the periodic table.

pHMeasures the acidity of a solution. It is the negative logof the concentration of the hydrogen ions in a

substance.

PhotonMassless packet of energy, which behaves like both awave and a particle.

Physical propertyA property that can be measured without changing thechemical composition of a substance.

Pi bondsA type of covalent bond in which the electron density isconcentrated around the line bonding the atoms.

PlanckPlanck contributed to the understanding of theelectromagnetic spectrum by realizing that therelationship between the change in energy andfrequency is quantized according to the equation E=hv where h is Planck's constant.

pOHMeasures the basicity of a solution. It is the negativelog of the concentration of the hydroxide ions.

Polar molecules

Molecule with a partial charge.

Potential energyThe energy an object has because of its composition orposition.

PressureForce per unit area.

Principal quantum number

The number related to the amount of energy anelectron has and therefore describing which shell theelectron is in.

ProductsThe compounds that are formed when a reaction goes

to completion.

ProportionEquality between two ratios.ProtonParticle found in a nucleus with a positive charge.Number of these gives atomic number.

Q

QuantumSomething which comes in discrete units, for example,money is quantized (divided into units); it comes inquanta (divisions) of one cent.

Quantum numbersSet of numbers used to completely describe anelectron.

R

Radiant energyEnergy which is transmitted away from its source, forexample, energy that is emitted when electronstransition down from one level to another.

RadiationEnergy in the form of photons.

RadioactiveSubstance containing an element which decays.


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RatioThe relative size of two quantities expressed as thequotient of one divided by the other; the ratio of a to bis written as a:b or a/b.

Reactants

Substances initially present in a chemical reaction.

Reduction reactionA reaction in which a substance gains at least oneelectron.

S

SaltsIonic compounds that can be formed by replacing one

or more of the hydrogen ions of an acid with anotherpositive ion.

ShellsWhere the electrons generally are. These shells arecomposed of 4 types of electron subshells: s, p, d and fsubshells.

Sigma bondsA type of covalent bond in which most of the electronsare located in between the nuclei.

Single bond

When an electron pair is shared by two atoms.

SI UnitStands for Systeme International d'Unites, aninternational system which established a uniform set ofmeasurement units.

SoluteThe substance (solid, liquid, or gas) dissolved in asolution, for example, the salt in saltwater.

Solution

Mixture of a solid and a liquid where the solid neversettles out, for example, saltwater.

SolventLiquid in which something is dissolved, for example,the water in saltwater.

Specific heatThe amount of heat it takes for a substance to beraised 1C.

Spontaneous reactionA reaction that will proceed without any outsideenergy.

State propertyA state property is a quantity that is independent ofhow the substance was prepared. Examples of stateproperties are altitude, pressure, volume, temperature

and internal energy.

States of matterSolid, liquid, gas and plasma. Plasma is a "soup" ofdisassociated nuclei and electrons, normally found onlyin stellar objects.

StoichiometryThe study of the relationships between amounts ofproducts and reactants.

STPStandard temperature and pressure. This is 0oC and 1

atm.

SubshellOne part of a level, each of which can hold differentnumbers of electrons.

T

Term


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Each compound or element in a chemical equation.

ThermodynamicsThe study of temperature, pressure, volume, andenergy flow in chemical reactions.

TitrationThe process used to take a solution of unknownconcentration with a solution of a known concentrationfor the purpose of finding out more about the unknownsolution.

V

Valence electronsThe electrons in the outermost shell of an atom.

Van der Waals equationAn equation for non-ideal gasses that accounts forintermolecular attraction and the volumes occupied bythe gas molecules.

VelocitySpeed of an object; the change in position over time.

VolumeMeasures the size of an object using lengthmeasurements in three dimensions.

W

WaveA signal which propagates through space, much like awater wave moves through water.

WavelengthOn a periodic curve, the length between twoconsecutive troughs (low points) or peaks (high points).

Weak acidSubstances capable of donating hydrogen but do notcompletely ionize in solution.

Weak bases

Substances capable of accepting hydrogen but do notcompletely ionize in solution.

WorkExpression of the movement of an object against someforce.

chem dictionary1

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