ATOMIC MASS
Atoms on the degree of precision
and smallness so it was difficult to estimate their atomic masses, however it
has been possible to assign their mass with great accuracy, for example, it has
found that a hydrogen atom mass reach 1.64×10-24 g.
it has also been possible to obtain
relative masses of atoms by setting the mass of elements with another element,
provided that the relative number of atoms in the compounds is known, so atomic
mass used to express an ele- ment mass for another element atom mass and it is agreed
to use in determining the relative masses of all the elements of the periodic table.
In 1961 in Geneva held a
Conference of the International Union of Pure and Applied Chemistry (IUPAC)
which was agreed on the definition of the standard unit of atomic mass and Atomic
Mass Unit named after (AMU) as equivalent to one of twelve part of carbon isotope
atom mass 12 and that it's atomic mass considered equal to 12 units and
therefore:-
Atomic mass unit
(amu) = (mass of an atom of carbon isotope 12)/12
i.e.; 1 (amu)=
(1/12) mass of an atom of carbon isotope 12
As the mass of carbon 12 isotope
atom=
Thus, the atomic mass we use today
and found in the periodic table are not ac- tual masses, but relative masses
show the relationship in terms of atomic mass between different atoms. For example,
the atomic mass of hydrogen isotope 1 is (1/12) the atomic mass of the isotope carbon-12
which is about 1 amu, either nucleus oxygen 16 have mass equal to(16/12) or
(4/3) from the mass of carbon 12 isotope, so when atomic mass estimates in grams
it called the gram-atomic mass.
Atomic mass unit
Atomic mass unit (AMU or amu) An
atomic mass unit (symbolized AMU or amu) is defined as pre- cisely 1/12 the
mass of an atom of carbon-12. The carbon-12 (C-12) atom has six protons and six
neut- rons in its nucleus.
The gram-atomic mass for oxygen = 16
g and for silver= 107.9 g and each mass of these masses has Avogadro's number of
atoms which is equal to 6.023×10*23 atoms, for example:
1 g of hydrogen contains 6.023×10*23 atoms of
hydrogen
2 39 g of potassium contain 6.023×10*23 atoms
of potassium
3 207 g of lead contain 6.023×10*23 atoms of
lead
The absolute atomic mass is the
mass of one atom of the element. i.e.;
The absolute atomic mass of an
element=gram-atomic mass of the element/ Avogadro's number
Example
Calculate the absolute atomic mass
of the oxygen given that it's atomic mass is equal to 16.
Solution:
The absolute atomic mass of an element=gram-atomic
mass of the element/ Avogadro's number
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