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Chapter 5 and 6:
Atomic Structure and
Chemical Names and
Formulas
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Atoms/Elements
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Subatomic Particles
• Protons and electrons are the only particles in
an atom that have a charge.
• Protons and neutrons have essentially the same
mass (1 unit each).
• The mass of an electron is so small we ignore it.
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Symbols of Elements
Elements are symbolized by one or two
letters.
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Atomic Number
All atoms of the same element have the same
number of protons:
The atomic number (Z)
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Atomic Mass
The mass of an atom in atomic mass units
(amu) is the total number of protons and
neutrons in the atom.
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Isotopes
• Isotopes are atoms of the same element with
different masses.
• Isotopes have different numbers of neutrons.
11
C
6
12
C
6
13
C
6
14
C
6
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Atomic Mass
Atomic and
molecular masses
can be measured
with great accuracy
with a mass
spectrometer.
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Average Mass
• Because in the real world we use large
amounts of atoms and molecules, we
use average masses in calculations.
• Average mass is calculated from the
isotopes of an element weighted by
their relative abundances.
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Periodic Table
• It is a systematic
catalog of the
elements.
• Elements are
arranged in order
of atomic number.
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Periodicity
When one looks at the chemical properties of
elements, one notices a repeating pattern of
reactivities.
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Periodic Table
• The rows on the
periodic chart are
periods.
• Columns are groups.
• Elements in the same
group have similar
chemical properties.
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Groups
These five groups are known by their names.
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Periodic Table
Nonmetals are
on the right
side of the
periodic table
(with the
exception of
H).
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Periodic Table
Metalloids
border the
stair-step line
(with the
exception of
Al, Po, and
At).
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Periodic Table
Metals are
on the left
side of the
chart.
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Diatomic Molecules
These seven elements occur naturally as
molecules containing two atoms.
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Compounds/Molecules/Ions
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Chemical Formulas for
Compounds
The subscript to the right
of the symbol of an
element tells the number
of atoms of that element
in one unit of the
compound.
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Law of Constant Composition
Joseph Proust (1754–1826)
• This is also known as the law of definite proportions.
• It states that the elemental composition of a pure
substance never varies, whether it is a single element
or a combination of elements in a compound.
• For example, H2O (water) is always made of two
hydrogen for every one oxygen.
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Chemical Formulas of Molecules
Molecular compounds
are composed of
molecules and almost
always contain only
nonmetals. They are
joined by covalent bonds,
which means they share
electrons.
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Types of Formulas for Molecules
• Empirical formulas give the lowest
whole-number ratio of atoms of each
element in a compound. Ex: CH2O
• Molecular formulas give the exact
number of atoms of each element in a
compound.Ex: C6H12O6 or C3H6O3
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Ways Formulas can be Visually
Represented
• Structural formulas show the
order in which atoms are bonded.
• Perspective drawings also show
the three-dimensional array of
atoms in a compound.
• Ball and Stick drawings show 3D
shape and relative sizes and
organization of atoms in
molecule.
• Space Filling Models more
accurately shows what the
molecule looks like…
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Nomenclature of Binary Molecules
• The less electronegative
atom is usually listed first
(furthest to the left or lowest
down on the periodic table).
• A prefix is used to denote
the number of atoms of
each element in the
compound (mono- is not
used on the first element
listed, however) .
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Nomenclature of Binary Molecules
• The ending on the more
element written second
is changed to -ide.
– CO2: carbon dioxide
– CCl4: carbon tetrachloride
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Nomenclature of Binary Molecules
• If the prefix ends with a
or o and the name of the
element begins with a
vowel, the two
successive vowels are
often elided into one.
N2O5: dinitrogen pentoxide
Practice Problems # 37, 38 on pg 159.
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Ions
• Some atoms gain or lose electrons to bond. When atoms lose or
gain electrons, they become ions.
– Cations are positive and are formed by elements on the left side of
the periodic chart (metals).
– Anions are negative and are formed by elements on the right side
of the periodic chart (non-metals).
– Ionic charge can be predicted by determining how many electrons
an atom has to lose or gain to become like the nearest stably
arranged noble gas.
Atoms,
– Practice Problems 1 and 2 on pg 136 and 16 and 17 on pg 145. Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Ionic Bonds
Ionic compounds (such as NaCl) are generally
formed between metals and nonmetals. After
the atoms lose or gain electrons they have a
charge. The opposite charges attract to each
other creating the bond.
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Writing Formulas for Ionic Compounds
• Because all compounds are electrically
neutral, one can determine the formula of an
ionic compound this way:
– The charge on the cation becomes the subscript
on the anion.
– The charge on the anion becomes the subscript
on the cation.
– If these subscripts are not in the lowest wholenumber ratio, divide them by the greatest common
factor.
Atoms,
– Practice Problems #24, 25 on pg 151.
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Common Cations
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Common Anions
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Nomenclature for Ionic Compounds
• Write the name of the cation.
• If the anion is an element, change its ending to ide; if the anion is a polyatomic ion, simply write
the name of the polyatomic ion. (No prefixes are
used)
• If the cation can have more than one possible
charge, write the charge as a Roman numeral in
parentheses.
• Do Practice Problems # 26-29 on pgs 153-156.
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Nomenclature of Acids
• If the anion in the acid
ends in -ide, change
the ending to -ic acid
and add the prefix
hydro- .
– HCl: hydrochloric acid
– HBr: hydrobromic acid
– HI: hydroiodic acid
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Acid Nomenclature
• If the anion in the acid
ends in -ate, change
the ending to -ic acid.
– HClO3: chloric acid
– HClO4: perchloric acid
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.
Acid Nomenclature
• If the anion in the acid
ends in -ite, change
the ending to -ous
acid.
– HClO: hypochlorous
acid
– HClO2: chlorous acid
Practice Problem #40 on pg 160.
Atoms,
Molecules,
and Ions
© 2009, Prentice-Hall, Inc.