The pH of an aqueous solution is the reciprocal of the
logarithm of the concentration of hydrogen ions
in the solution (i.e. the negative of the logarithm of
the hydrogen ion concentration).
pH = - log10[H(+)]
A neutral solution has a pH of 7.0. A pH less
than 7.0 indicates an acid solution, while a pH
above 7.0 indicates an alkaline solution. The scale
was introduced by S.P. Sorensen.
Paramagnetism in the transition
elements
is caused by the presence of unpaired electrons in the d sub-orbital,
and results in these elements being attracted by a magnetic field.
- The Pauli's exclusion principle
- specifies that no two electrons which are in the orbitals about a nucleus of an atom
may have identical Quantum Numbers.
- The periodic law
- states that there are regularly repeating properties on
going from element to element with increasing atomic number
of the elements.
These properties are best summarised in the modern
version of the periodic table.
The first attempt at defining a periodic law was
the octet rule.
The periodic table is the structured arrangement of the elements in a chart that accentuates
the relationships between the chemical properties of the different elements.
The structure of the modern version of the periodic table is explained by the
electronic configuration
of the elements.
Permanent hardness in water is caused by high levels of
calcium salts (e.g. calcium carbonate) and magnesium salts
(e.g. magnesium carbonate) being dissolved in the water.
The peroxide effect results in the formation of a different product from that predicted by the
Markownikoff Rule
when an addition reaction takes place in the presence of a peroxide. Peroxides give rise to
free radicals, and a free radical mechanism
for a chain reaction is believed to be responsible for the products observed.
In the presence of a peroxides (which give rise to free radicals), the
Anti-Markownikoff Rule specifies
the orientation with which a small asymmetric molecule adds across the double bond of an
alkene, because under
these conditions the reactants add across a double bond
in the opposite orientation to that specifies in
the Markownikoff's Rule.
peroxide
HH H HH H HHH
HCC=CH ==> HCC+CH==> HCCCH
H H H HHBr
1-Bromopropane
These peroxides can arise from exposure of the
propene, or other alkenes, to air or they can result
from the addition of an organic peroxide
(e.g. benzoyl peroxide) which is added deliberately to
give the product of the required stereochemistry. This is
called the peroxide effect and a free radical chain
reaction is believed to be responsible for it.
Peroxides, R-O-O-R, are organic
molecules which contain the peroxide linkage, -O-O-, within the molecule. Peroxides readily
give rise to free radicals, because the
oxygen to oxygen bond is easily broken in these organic molecules.
R-O-O-R ==> 2 R-O*
Peroxide Peroxide
Free Radical
The most important organic peroxide is benzoyl peroxide, (C6H5COO)2, which is the
initiator used in the polymerisation of
many industrially important polymers
(e.g. fillers, etc) and adhesives (e.g. superglue, etc.).
Peroxide are also the group of inorganic compounds
that contain the peroxide ion, O2(2 -).
Perspex is a trade name for plastics made from polymethylmethacrylate.
Petrochemicals are the industrially important organic
chemicals which are derived from petroleum or natural gas.
Petrol (i.e. Gasoline) is a complex mixture of
hydrocarbons containing 5 to 10 carbon atoms in each molecule.
A physical change is a change of state of a substance,
where only the physical properties of the substance are
changes and the chemical composition of the substance
is unaltered.
The physical properties of a substance are those
permanent properties which describe the physical
characteristics of the material.
Start of Hypertext ....
Elements ....
Compounds ....
Index
Hypertext Copyright (c) 2000 Donal O'Leary. All Rights Reserved.