Pi Bonds (p-Bonds) between atoms are formed by the side-on overlap
of the atomic orbitals on the different atoms.
Pig iron is the impure form of iron produced in a blast
furnace, which is then cast into pigs (i.e. blocks) for
converting at a later date into cast iron, steel, etc.
A pipette is a graduated glass volumetric apparatus used to
deliver a stated quantity of liquid in volumetric analysis by
Planck's constant, h, is the proportionality constant defining the
relationship between the energy, E, associated with a photon
and the frequency, v, of that photon.
E = h x v
In 1900AD, Plank made the assumption that the energy of
light, and of radiation in general, may be absorbed and
emitted in only in quanta (i.e. discrete packets of
h = 6.6 ( 10 ^ -27 erg seconds
When the atoms that are linked by a covalent
bond have significantly different
electronegativities, the electron is likely to spend a greater time near the atom of higher
negativity, giving to an unequal distribution of charge between the atoms. Thus, a
dipole (i.e. a separation of charge along the length of the bond) is formed and the resulting
bond is a polar covalent bond between the atoms.
In general, the polar bond is stronger than the covalent bond
from which it derives. Polar compounds (i.e. compounds containing
polar bonds) tend to have hydrogen bonding between
different molecules, and to have higher boiling points and higher
melting points than would be the case in the absence of
such hydrogen bonding.
A polar molecule is one that has a dipole moment (i.e. one in
which there is some separation of charge in the chemical bonds), so
that one end of the molecule has a positive charge and the
other a negative charge.
Pollution is an undesirable change in the physical, chemical,
or biological characteristics of the natural environment,
brought about by man's activities. There are two main
classes of pollutants
- those that are biodegradable and which can be rendered harmless
by natural processes and need therefore cause no permanent harm
if adequately dispersed or treated; and
- those that are nonbiodegradable, which eventually accumulate
in the environment and may be concentrated in food chains. Pollution can occur in the air or
Polyhydric alcohols contain several hydroxyl groups in the
molecule and are normally obtained by the reduction of sugars.
For example, sorbital is obtained by the reduction of glucose.
(CHOH)4 ==> (CHOH)4
Polymers are the long chain molecules obtained when a
large number of small molecules combine together to form
a smaller number of large molecules. Polymers are long
chain molecules which have physical properties which are
significantly different from the monomers (i.e. the
short chain molecules) from which they are made. Polymers
are the basis for a wide range of materials which have become
indispensable in modern society, including synthetic fibers (rayon, nylon, terelene, etc), rubbers and
plastics (polystyrene, polythene, PVC, etc.), and the
structural polymers (carbon fiber, etc).
Polymerization is the process by which many small molecules
join together to form large molecules. The reactants
(i.e. the small molecules) are called monomers and long
chain products of the polymerisation process are called
polymers. Many of useful materials are natural polymers
(e.g. wool, cotton, linen, etc) or synthetic
polymers (e.g. nylon, terelyene, rayon, etc).
There are two general methods for preparing polymers, which involves the linking of small
molecules together to form long chain molecules. The term
"addition polymerisation" is
used where small molecules are added directly to each other and the term
polymerisation" is used where
a molecule of water (or other small molecule) is released during the assembly process.
In general, addition polymerisations tend to proceed by
a Free Radical Mechanism
, while condensation polymerisation tends to proceed by an ionic mechanism.
The high pressure gas phase polymerisation of
ethene to form Polythene involves a free radical mechanism.
Thus, when ethylene is heated under great pressure in
the presence of a suitable catalyst a large number of
molecules of ethene combine together to form a much
smaller number of molecules of Polythene, (C2H4)n,
Positive ions (i.e. cations) are atoms or group of atoms
that has either lost one or more electrons, making them
The potential energy is the energy possessed by a
body due to its position. The potential energy varies when
a body moves from one position to another.
Potential Energy = Weight x Distance moved vertically against gravity.
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