The density of a substance is a physical property of the substance. It is
the mass of a substance occupying a certain volume. The unit of density is
usually expressed as the mass divided by the volume.
The dipole moment is a measure of the extent to which a separation of charge
exists within a molecule.
Dissociation
The process by which ionic compounds break up into their individual ions in
the presence of water molecules.
Electrolyte
These are substances that produce ions in aqueous
solution. It is also a solution that conduct an electric current. Ionic compounds and strong acids
and bases are strong electrolytes.
Electronegativity
is a measure of the tendency of an atom to attract electrons to itself in
a covalent bond.
Electrolysis
is process used to decompose water by using electricity. The products of the
electrolysis of water are hydrogen gas and oxygen gas.
Electrons
Electrons are negatively charged fundamental particles. They are found outside
the nuclei of all atoms. The mass of an electron is 1/1835 of the mass of
a proton.
Element
A substance in which all the atoms have the same atomic number. It is a substance
that cannot be broken down into simpler substances.
Empirical formula
Also known as the simplest formula. It is the chemical formula that gives
the simplest whole-number ratio of atoms of each element in a compound.
In some compounds the empirical formula is the same as the molecular
formula . For example,
For water, H2O is the molecular formula. H2O is
also the empirical formula because the ratio of H to O in the molecular
formula is also the simplest whole-number ratio.
For benzene, C6H6 is the molecular formula. The
empirical formula is CH, the simplest ratio of C to H.
(Molar mass of compound) /
(Mass of the Empirical formula) = Number of Empirical Formula Units
Endothermic reaction
A chemical reaction that proceeds only when it takes up or absorbs energy
from the surroundings.
Energy
When samples of matter react chemically, energy is almost always absorbed
or released. So, the study of energy is an integral part of the study of chemistry.
Exact numbers
Exact numbers are numbers are integers and there are no uncertainty associated
with them. For example:
12 items of anything make up to a dozen of anything. 12 is an exact
number.
There are 1000 meters in a kilometer. 1000 is an exact number.
Exothermic reaction
A chemical reaction that releases heat energy.
Fahrenheit
A temperature scale based on a value of 32 oF as the melting point
of ice and 212oF as the boiling point of water.
The formula mass of a substance is the sum of the atomic masses of all atoms
in a formula unit of the substance expressed in amu.
Formula unit
The smallest unit of an ionically bonded substance. For example, the formula
unit of sodium chloride is NaCl.
Ground state
The ground state of the electrons in an atom is the energy associated with
the arrangement of the electrons such that they are at the lowest possible
energy level. Because electrons are constant moving, the ground state energy
is not zero.
Group of elements
A vertical column of elements in the periodic table.
Halogens
All the elements in Group VIIA of the periodic table.
Heterogeneous mixture
Heterogeneous mixtures do not have the same composition and properties throughout
a sample. Some examples of heterogeneous mixtures are: iced tea, blood, milk.
Homogeneous mixture
Homogeneous mixtures are called solutions. Homogeneous mixtures have the same
composition and properties that are uniform throughout a sample, but different
samples may have different properties. A homogeneous mixture can be separated
into its components by appropriate physical changes.
Some examples of solutions are: gasoline, seawater, tea.
