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Atoms,Molecules,
and Ions
Chapter 2Atoms, Molecules,
and Ions
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Atoms,Molecules,
and Ions
Law of Constant CompositionJoseph Proust (1754–1826)
Also known as the law of definiteproportions.
The elemental composition of a puresubstance never varies.
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Atoms,Molecules,
and Ions
Law of Conservation of Mass
The total mass of substances presentat the end of a chemical process is the
same as the mass of substances presentbefore the process took place.
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Atoms,Molecules,
and Ions
The Nuclear Atom
Since some particleswere deflected at largeangles, Thompson’s
model could not becorrect.
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Atoms,Molecules,
and Ions
The Nuclear Atom
Rutherford postulated a very small, densenucleus with the electrons around theoutside of the atom.
Most of the volume of the atom is emptyspace.
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Atoms,Molecules,
and Ions
Subatomic Particles
Protons and electrons are the only particles thathave a charge.
Protons and neutrons have essentially the same
mass.The mass of an electron is so small we ignore it.
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Atoms,Molecules,
and Ions
Atomic Number
All atoms of the same element have the
same number of protons:The atomic number (Z)
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Atoms,Molecules,
and Ions
Atomic Mass
The mass of an atom in atomic mass units
(amu) is the total number of protons andneutrons in the atom.
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Atoms,Molecules,
and Ions
Isotopes:
Atoms of the same element with different masses.
Isotopes have different numbers of neutrons.
116C
126C
136C
146C
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Atoms,Molecules,
and Ions
Average Mass
Because in the real world we use largeamounts of atoms and molecules, we use
average masses in calculations.Average mass is calculated from theisotopes of an element weighted by their
relative abundances.
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Atoms,Molecules,
and Ions
Periodic Table:
A systematic catalogof elements.
Elements arearranged in order of atomic number.
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Atoms,Molecules,
and Ions
Periodicity
When one looks at the chemical properties of
elements, one notices a repeating pattern of reactivities.
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Atoms,Molecules,
and Ions
Periodic Table
The rows on the periodicchart are periods.
Columns are groups.
Elements in the samegroup have similar chemical properties.
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Atoms,Molecules,
and Ions
Groups
These five groups are known by their names.
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Atoms,Molecules,
and Ions
Diatomic Molecules
These seven elements occur naturally asmolecules containing two atoms.
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Atoms,Molecules,
and Ions
Types of Formulas
Empirical formulas give the lowest whole-number ratio of atoms of each element in
a compound.Molecular formulas give the exact number of atoms of each element in a compound.
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Atoms,Molecules,
and Ions
Types of Formulas
Structural formulas show theorder in which atoms arebonded.
Perspective drawings alsoshow the three-dimensionalarray of atoms in a compound.
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Atoms,Molecules,
and Ions
Ions
When atoms lose or gain electrons, theybecome ions.
Cations are positive and are formed by elements on theleft side of the periodic chart.
Anions are negative and are formed by elements on theright side of the periodic chart.
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Atoms,Molecules,
and Ions
Writing Formulas
Because compounds are electrically neutral,one can determine the formula of a compound
this way:The charge on the cation becomes the subscript on theanion.
The charge on the anion becomes the subscript on thecation.
If these subscripts are not in the lowest whole-number ratio, divide them by the greatest common factor.
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Atoms,Molecules,
and Ions
Common Cations
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Atoms,Molecules,
and Ions
Common Anions
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Atoms,Molecules,
and Ions
Inorganic Nomenclature
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Atoms,Molecules,
and Ions
Patterns in Oxyanion Nomenclature
When there are two oxyanions involvingthe same element:
The one with fewer oxygens ends in -ite● NO2− : nitrite; SO32− : sulfite
The one with more oxygens ends in -ate
● NO3− : nitrate; SO42− : sulfate
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Atoms,Molecules,
and Ions
Patterns in Oxyanion Nomenclature
The one with the fewest oxygens has the prefix hypo-and ends in -ite
● ClO− : hypochlorite
The one with the most oxygens has the prefix per - andends in -ate
● ClO4− : perchlorate
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Atoms,Molecules,
and Ions
Acid Nomenclature
If the anion in the acidends in -ide, change theending to -ic acid and
add the prefix hydro- :HCl: hydrochloric acid
HBr: hydrobromic acid
HI: hydroiodic acid
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Atoms,Molecules,
and Ions
Acid Nomenclature
If the anion in the acidends in -ite, change theending to -ous acid :
HClO: hypochlorous acid
HClO2: chlorous acid
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Atoms,Molecules,
and Ions
Acid Nomenclature
If the anion in the acidends in -ate, change theending to -ic acid:
HClO3: chloric acid
HClO4: perchloric acid
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Atoms,Molecules,
and Ions
Nomenclature of BinaryCompounds
The less electronegativeatom is usually listed first.
A prefix is used to denotethe number of atoms of each element in thecompound (mono- is notused on the first element
listed, however.)
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Atoms,Molecules,
and Ions
Nomenclature of BinaryCompounds
The ending on the moreelectronegative element ischanged to -ide.
CO2: carbon dioxide
CCl4: carbon tetrachloride
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Atoms,Molecules,
and Ions
Nomenclature of BinaryCompounds
If the prefix ends with a or o and the name of theelement begins with a
vowel, the two successivevowels are often elidedinto one:
N2O5: dinitrogenpentoxide
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