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10.1 INTRODUCTION: THE CONCEPT OF PROTON AND
THE PHYSICOCHEMICAL PROCESS OF PROTONATION IN
CHEMISTRY
10.1.1 PROTON IN PHYSICS
Proton is a subatomic hadron particle with the symbol p or p + with a posi-
tive electric charge of 1 elementary charge. One or more protons are pres-
ent in the nucleus of each atom, along with neutrons.
The proton is also stable by itself. Free protons are emitted directly in
some rare types of radioactive decay, and result from the decay of free
neutrons from other radioactivity. They soon pick up an electron and be-
come neutral hydrogen atom. Free protons may exist in plasmas or in cos-
mic rays in vacuum.
The proton particle comprises three fundamental particles: two up
quarks and one down quark. It is about 1.6-1.7 fm in diameter.
10.1.2 PROTON IN CHEMISTRY
In chemistry, the number of protons in the nucleus of an atom is known as
the atomic number, which determines the chemical element to which the
atom belongs. In chemistry, the term proton refers to the hydrogen ion,
H + . The proton itself is some 1,800 times smaller than a hydrogen atom,
and therefore is extremely reactive. The free proton has an extremely short
lifetime in chemical systems. It reacts rapidly with any available molecule.
In aqueous solution, it forms the hydronium ion, which in turn is further
solvated by water molecules in clusters such as [H 5 O 2 ] + and [H 9 O 4 ] + .
The transfer of H + in an acid-base reaction is usually referred to as
“proton transfer.” The acid is referred to as a proton donor and the base as
a proton acceptor. Likewise, biochemical terms such as proton pump and
proton channel refer to the movement of hydrated H + ions.
10.1.3 BOHR MODEL IN GENERAL AND STRUCTURE OF
HYDROGEN ATOM
According to Bohr model of atomic structure, there are quantized energy
levels in the atom called stationary states where the electrons are likely
found and revolve round the nucleus. Therefore, atom is a multistoried
building with shells/energy levels as floors.
 
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