Download Chapter 3 Atoms: The Building Blocks

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CHEMISTRY CHAPTER 3
(Atoms: The Building Block of Matter)
The Law of Conservation of Mass
Mass is neither destroyed nor created during ordinary
chemical reactions or physical changes.
The Law of Definite Proportions
A chemical compound contains the same elements in
exactly the same proportions by mass
An atom is the smallest particle of an element that
retains the properties of that element
All matter is made up of atoms
The nucleus is the very small dense positively charged
central part of an atom
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An atoms electron cloud is the region in which the
electrons orbit the nucleus
An electron cloud is made up of negatively charged
particles called electrons
Electrons orbiting a nucleus at a certain distance is said
to be on the same energy level
An energy level is a particular area in which one or more
electrons orbit the nucleus
Only a certain number of electrons can occupy the same
energy level
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Protons are positively charged particles [in the nucleus
of an atom]
Neutrons are neutral particles [in the nucleus of an atom]
The atomic number is the number of protons in the
nucleus of an atom
Li Atomic number = 3
so,
3 protons
3 neutrons
3 electrons
The mass number is the total number of protons and
neutrons in the nucleus of an isotope.
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Atoms of the same element that have different masses
(different number of neutrons) are called isotopes
Ex: The three isotopes of Hydrogen
Hydrogen-1
(protium)
Hydrogen-2
(duetrium)
Hydrogen-3
(tritium)
mass # = 1
mass # = 2
mass # = 3
A nuclide is a general term for any isotope of any
element
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The number 6.02 x 1023 is referred to as a mole
6.02 x 1023 is the Avogadro number
6.02 x 1023 = 602,000,000,000,000,000,000,000
six hundred, two hextillion
The Average-atomic weight (Atomic mass) of an
element is equal to the mass of one mole of atoms
This number can be found on the periodic chart.
*Each of the following are used as synonyms for
average-atomic mass:
gram formula weight (GFW)
gram molecular weight (GMW) (most common use)
molecular weight
(MW)
formula weight
(FW)
formula mass
(FM)
and others