Chemistry 1
To solve this problem, chemists developed a concept of how to express the
exact number of atoms or particles contained in a given mass of substance.
This is called the mole
A mole denotes a collection of large fixed number of particles
(atom,ions,molecules)It is defined as the amount of substance containing the
same number of atoms as 12.0000g of pure
carbon- 12. The symbol for the number of mole is n and its unit is abbreviated
as mol.
But how many atoms or molecules does a mole of any substance contains?
Amadeo Avogadro an Italian lawyer and physicist pioneered the studies on
counting atoms and molecules. He concluded that a mole of any substance
contains exactly6.022x1023.This is called Avogadro’s number. the term refers
to the ions, atoms, or molecules.
Quarter1Module 6;
Stoichiometry
“ Atomic Mass, Avogadro’s
Number, The mole concept”
I.
Learning Competencies
1.
Explain relative atomic mass and average atomic mass
2.
Define mole
3.
Illustrate Avogadro’s Number with examples
4.
Determine the molar mass of elements and compounds
5.
Calculate the mass of the given number of moles of an
element or compound at vice versa
6.
Calculate the mass of the given number of particles of
an element or compound at vice versa
For free elements existing as single atoms such as gold (Au), silver (Ag),
and sulfur (S), we count their particles by atoms; for ionic compounds like NaCl,
we express the number of particles by formula units; for covalent compounds
such as CO2, particles are counted as molecules and for the charged particles,
they are counted as ions.
Note:
1 mole of any substance= 6.02 x 1023 particles
1 mole of carbon, C= 6.02 x 1023 molecules of carbon
1 mole of table salt, NaCl=6.02 x 1023 formula units of NaCl
1 mole of Potassium ion, K+ 6.02 x 1023 ions of potassium
THE MOLE CONCEPT
Clothes, fruits, pens, and books are some of the materials we usually
buy by piece, however, here are materials we need to buy by group. For
example we buy shoes and socks by pair; eggs by the dozen; paper clips by the
box, and plates by the set. The terms pair, dozen box and set are few of the
terms use to count substances. We may call them the counting units.
These counting units refer to materials hat are tangible and visible. How about
the materials that are invisible like atoms and molecule?
THE MOLAR MASSES OF COMPOUNDS
In computing the number of moles of given substances, it is necessary that
we know their molar masses or their atomic masses. The complete list of the atomic
masses of elements is found in the periodic table of elements. The molar masses of
1
compound, however, are computed. They are equal to the sum of the atomic
masses of all atoms present in the compounds. The unit commonly used to describe
atomic and molar masses is the gram/mole (g/mol)
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