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.
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.
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
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.
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 concentration 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.
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.
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.
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.
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.
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 0°C and 1 atm.
sublevel
One part of a level, each of which can hold different numbers of electrons.
