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ASU Chemistry Glossary
Click on the first letter of the term.
[a][b][c][d][e][f][g][h][i][j][k][l][m][n][o][p][q][r][s][t][u][v][w][x][y][z]
ASU Chem Main Page or Shodor Home Page
A
- acceleration
- Measure of how fast velocity is changing, so we can think of it as the change in
velocity over time. The most common use of acceleration is acceleration due to gravity which can also appear as the gravitational constant (9.8 m/s2).
- acid
- Compound that gives off H+ ions in solution.
- acidic
- Describes a solution with a high concentration of H+ ions.
- anion
- Ions with a negative charge
- anode
- The electrode where electrons are lost (oxidized) in redox reactions.
- area
- Measures the size of a surface using length measurements in two dimensions.
- associativity
- A 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.
- atom
- The smallest object that retains properties of an element. Composed
of electrons and a nucleus (containing protons and neutrons).
- atomic number
- Number of protons in an element.
- Avagadro's number
- Number representing the number of molecules in one (1) mole: 6.023 * 1023.
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B
- base
- Substance which gives off hydroxide ions (OH-) in solution.
- basic
- Having the characteristics of a base.
- Bohr's atom
- Bohr made significant contributions to the atom. He understood the line spectra-- the reason why only certain wavelengths are emitted when atoms jump down levels.
- buffer solutions
- Solutions that resist changes in their pH, even when small amounts of acid or base are
added.
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C
- catalyst
- Substance that speeds up a chemical process without actually changing the products of
reaction
- cathode
- Electrode where electrons are gained (reduction) in redox reactions.
- cations
- Ion with a positive charge.
- central atom
- In a Lewis structure, usually the atom that is the most electronegative.
- 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.
- chemical changes
- Processes or events that have altered the fundamental structure of something.
- chemical equation
- An expression of a fundamental change in the chemical substances.
- closure
- A mathmatical term which says that if you operated on any two real numbers A and B with +,-,* or /, you get a real number
- colligative properties
- Properties of a solution that depend only on the number of particles dissolved in it,
not the properties of the particles themselves. The main colligative properties addressed
at this web site are boiling point elevation and freezing point depression.
- combustion
- When substances combine with oxygen and release energy.
- commutativity
- A math property which states: A+B=B+A and A*B=B*A
- compound
- Two or more atoms joined together chemically, with covalent or ionic bonds.
- concentration
- The amount of substance in a specified space.
- 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.
- covalent bonds
- When two atoms share at least one pair of electrons.
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D
- daughter isotope
- In a nuclear equation the compound remaining after the parent isotope (the original
isotope) has undergone decay. A compound undergoing decay, such as alpha decay, will break
into an alpha particle and a daughter isotope.
- decay
- Change of an element into a different element, usually with some other particle(s) and
energy emitted.
- decimal
- The number of digits to the right of the decimal point in a number
- dense
- A compact substance or a substance with a high density.
- density
- Mass per unit volume of a substance.
- dipole-dipole forces
- Intermolecular forces that exist between polar molecules. Active only when the
molecules are close
together. The strengths of intermolecular attractions increase when polarity increases.
- dispersion forces (also called London dispersion forces)
- Dispersion is an intermolecular attraction force that exists between all molecules.
These forces are the result of the movement of electrons which cause slight polar
moments. Dispersion forces are generally very weak but as the molecular weight increases so does their strength.
- dissociation
- Breaking down of a compound into its components.
- distributivity
- 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.
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E
- effusion
- Movement of gas molecules through a small opening.
- electrochemical cell
- Gives an electric current with a steady voltage as a result of an electron transfer reaction.
- electrodes
- 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
- Complete range of wavelengths which light can have. These include
infared, ultraviolet, and all other types of electromagnetic radiation, as
well as visible light.
- electron
- One of the parts of the atom having a negative charge. Indivisible particle with a
charge of -1.
- electron geometry
- Structure of a compound based on the arrangement of its electrons.
- electronegativity
- Measure of a substances's ability to attract electrons.
- electrostatic forces
- Forces between charged objects.
- element
- Substance consisting of only one type of atom.
- empirical formula
- Formula showing the simplist ratio of elements in a compound.
- endothermic
- Reaction that absorbs heat from its surroundings as the reaction
proceeds.
- energy
- Ability to do work.
- enthalpy
- Change in heat.
- entropy
- Measure of the disorder of a system.
- equilibrium
- When the reactants and products are in a constant ratio. The forward reaction and the reverse reactions occur at the same rate when a system is in equilibrium.
- equilibrium constant
- Value that expresses how far the reaction proceeds before reaching
equilibrium. A small number
means that the equilibrium is towards the reactants side while a large number means that the equilibrium is towards the products side.
- equilibrium expressions
- The expression giving the ratio between the products and reactants. The equilibrium expression is equal to the concentration of each product raised to its coefficient in a balanced chemical equation and multiplied together, divided by the concentrat
ion of the product of reactants to the power of their coefficients.
- equivelence point
- Occurs when the moles of acid equal the moles of base in a solution.
- exothermic
- Reaction that gives off heat to the environment.
- exponentiation
- Raising something to a power.
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F
- force
- An entity that when applied to a mass causes it to accelerate. Sir Isaac Newton's Second Law of mation states: the magnitude of a force = mass * acceleration.
- free electron
- Electron which is not attached to a nucleus.
- free energy
- The energy of a system that is available to do work at constant temperature and pressure.
- frequency
- Number of events in a given unit of time. When describing a
moving wave,
means the number of peaks which would pass a stationary point in a
given amount of time.
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G
- geiger counter
- Instrument that measures radiation output.
- Graham's law
- The rate of diffusion of a gas is inversely proportional to the square root of its molecular weight.
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H
- half life
- The amount of time it takes for half an initial amount to
disintegrate.
- Heisenberg Uncertainty principle
- This principle states that it is not possible to know a particle's
location and momentum precisely at any time.
- hydrogen bonding
- Strong type of intermolecular dipole-dipole atttraction. Occurs
between hydrogen and F, O or N.
- hydrolysis
- When water reacts with another substance and as a result the oxygen in water makes a bond with the substance.
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I
- ideal gas law
- PV=nRT
Describes the relationship between pressure (P),
temperature (T), volume (V), and moles of gas (n). It is not completely
accurate, and becomes less accurate as conditions become less ideal.
- identity
- A math property which states: A+0=A and A*1=A.
- intermolecular forces
- Forces between molecules.
- intramolecular forces
- Forces within molecules. Forces caused by the attraction and
repulsion of charged particles.
- inverse
- A math property which states: A+(-A)=0 and A*(1/A)=1
- ion
- Removing or adding electrons to an atom creates an ion (a charged
object very similar to an atom).
- ion-dipole forces
- Intermolecular force that exist between charged particles and
partially charged molecules.
- 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
- Energy required to remove an electron from a specific atom.
- ionizes
- When a substance breaks into its ionic components.
- isotopes
- Elements with the same number of protons but have different numbers of neutrons, and thus different masses.
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K
- kelvin
- The SI Unit of temperature. It is the degrees celsius plus 273.
- kinetic energy
- Energy an object has because of its mass and velocity. Objects that don't move have no kinetic energy. (Kinetic Energy=0.5* mass*velocity2.
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L
- Le Chatlier's principle
- States that a system at equilibrum will oppose any change in the equilibrium conditions.
- Lewis structures
- A way of representing molecular structures based on valence
electrons.
- limiting reagent
- The reactant that will be exhausted first.
- line spectra
- Spectra generated by excited substances. Consists of radiation with
only specific wavelengths.
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M
- mass number
- The number of protons and neutrons in an atom.
- mixture
- Composed of two or more substances, but each keeps its original
properties.
- molality
- The number of moles of solute (the material dissolved) per kilogram of solvent (what the solute is dissolved in).
- molar
- An term expressing molarity, the number of moles of solute/ liters of solution
- molarity
- The number of moles of solute (the material dissolved) per liter of solution. Used to express the concentration of a solution.
- mole
- A collection of 6.023* 1023 number of objects. Usually
used to mean molecules.
- molecular formula
- Shows the number of atoms of each element present in a molecule.
- molecular geometry
- Shape of a molecule, based on the relative positions of the atoms.
- molecular weight
- The combined weight (as given on the periodic table) of all the
elements in a compound.
- molecule
- Two or more atoms chemically combined.
- mole fraction
- The number of moles of a particular substance expressed as a fraction of the total number of moles.
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N
- neutral
- An object that does not have a positive or negative charge.
- neutron
- A particle found in the nucleus of an atom. It is almost identical in mass to a proton, but carries no electric charge.
- nm
- An abbreviation for nano-meters. A nano-meter is equal to 10-9 meters.
- nucleus
- The central part of an atom that contains the protons and neutrons.
Plural nuclei.
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O
- octet
- In Lewis structures the goal is to make almost all atoms have an octet. This means that they will have access to 8 electrons regularly, even if they do have to share some of them.
- orbitals
- An energy state in the atomic model which describes where an electron will likely be.
- oxidation number
- A number assigned to each atom to help keep track of the electrons during a redox-reaction.
- oxidation reaction
- A reaction where a substance loses electrons
- oxidation-reduction-reaction
- A reaction involving the transfer of electrons.
- oxyacid
- When one or more hydroxide (OH) groups are bonded to a central atom.
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P
- parent isotope
- An element that undergoes nuclear decay.
- partial pressures
- The pressure exerted by a certain gas in a mixture.
- particle
- Small portion of matter
- percent composition
- Expresses the weight ratio between different elements in a compound.
- periodic table
- Grouping of the known elements by their number of protons. There are
many other trends such as size of elements and electronegativity that are easily expressed in terms of the periodic table.
- pH
- Measures the acidity of a solution. It is the negative log of the concentration of the hydrogen ions in a substance.
- photons
- Massless packet of energy, which behaves like both a wave and a
particle.
- physical property
- A property that can be measured without changing the chemical composition of a substance.
- pi bonds
- A type of covalent bond in which the electron density is concentrated around the line bonding the atoms.
- Planck
- Planck contributed to the understanding of the electromagnetic
spectrum by realizing that the relationship between the change in energy
and frequency is quantized according to the equation delta E=hv where h is
Planck's constant.
- pOH
- Measures the basicity of a solution. It is the negative log of the concentration of the hydroxide ions.
- polar molecules
- Molecule with a partial charge.
- potential energy
- The energy an object has because of its composition or position.
- pressure
- Force per unit area.
- principal quantum number
- The number related to the amount of energy an electron has and
therefore describing which shell the electron is in.
- products
- The compounds that are formed when a reaction goes to completion.
- proportion
- An equality between two ratios.
- proton
- Particle found in a nucleus with a positive charge. Number of these
gives atomic number.
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Q
- quantum
- Something which comes in discrete units. Eg, money is quantized
(divided into units); it comes in quanta (divisions) of one cent.
- quantum numbers
- Set of numbers used to describe an electron's position.
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R
- radiant energy
- Energy which is transmitted away from its source. eg, energy that is
emitted when electrons transition down from one level to another.
- radiation
- Energy in the form of photons.
- radioactive
- Substance containing an element which decays.
- ratio
- The relative size of 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
- Substances initially present in a chemical reaction.
- reduction reaction
- A reaction in which a substance gains at least one electron.
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S
- salts
- Ionic compounds that can be formed by replacing one or more of the hydrogen ions of an acid with another positive ion.
- shells
- Where the electrons generally stay. There are 4 types of electron shells: s, p, d and f shells.
- sigma bonds
- A type of covalent bond in which most of the electrons are located in
between the nuclei.
- single bond
- When an electron pair is shared by two different elements.
- SI Unit
- Stands for Systeme International d'Unites, a international system
which established a uniform set of measurement units.
- solute
- What is dissolved in a solution eg, the salt in saltwater.
- solution
- Mixture of a solid and a liquid where the solid never settles out, eg
saltwater.
- solvent
- Liquid in which something is dissolved, eg the water in saltwater.
- 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.
- state property
- A state property is a quantity that is independent of how the
substance was prepared. Examples of state properties are altitude,
pressure, volume, temperature and internal energy.
- states of matter
- Solid, liquid, gas and plasma. Plasma is a "soup" of diassociated
nuclei and electrons, normally found only in stellar objects.
- stoichiometry
- The study of the relationships between amounts of products and
reactants.
- STP
- Standard temperature and pressure. This is 0oC and 1 atm.
- sublevel
- One part of a level, each of which can hold different numbers of
electrons.
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T
- term
- Each compound or element in a chemical equation.
- 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.
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V
- valence electrons
- The electrons in the outermost shell of an atom.
- van der Waals equation
- An equation for non-ideal gasses that accounts for intermolecular attraction and the volumes occupied by the gas molecules.
- velocity
- Speed of an object; the change in position over time.
- volume
- Measures the size of an object using length measurements in three dimensions.
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W
- wave
- A signal which propagates through space, much like a water wave moves
through water.
- wavelength
- On a periodic curve, the length between two consecutive troughs (low
points) or peaks (high points).
- weak acid
- Substances capable of donating hydrogen but do not completely ionize
in solution.
- weak bases
- Substances capable of accepting hydrogen but do not completely ionize in solution.
- work
- Expression of the movement of an object against some force.
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