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Chapter 2
Atoms, Molecules,
and Ions
John D. Bookstaver
St. Charles Community College
Cottleville, MO
Lecture Presentation
2012 Pearson Education, Inc.
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Atomic Theory of Matter
The theory that
atoms are thefundamental
building blocks
of matter
reemerged in
the earlynineteenth
century,
championed
by John
Dalton.
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Dalton's Postulates
Each element is
composed of extremely
small particles calledatoms.
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Dalton's Postulates
All atoms of a given
element are identical to
one another in massand other properties,
but the atoms of one
element are different
from the atoms of allother elements.
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Dalton's Postulates
Atoms of an element
are not changed into
atoms of a differentelement by chemical
reactions; atoms are
neither created nor
destroyed in chemicalreactions.
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Dalton's Postulates
Compounds areformed when atoms ofmore than one elementcombine; a givencompound always hasthe same relativenumber and kind of
atoms.
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Law of Conservation of MassThe total mass of substances present at the
end of a chemical process is the same as the
mass of substances present before the
process took place.
The law of constant composition
The law of multiple proportions
The law of conservation of energy
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Practice Questions
1) Which one of the following is not one of the postulates of Dalton's atomic theory?
A) Atoms are composed of protons, neutrons, and electrons.
B) All atoms of a given element are identical; the atoms of different elements aredifferent and have different properties.
C) Atoms of an element are not changed into different types of atoms by chemical
reactions: atoms are neither created nor destroyed in chemical reactions.
D) Compounds are formed when atoms of more than one element combine; a given
compound always has the same relative number and kind of atoms.
E) Each element is composed of extremely small particles called atoms.
2) Consider the following selected postulates of Dalton's atomic theory:
(i) Each element is composed of extremely small particles called atoms.
(ii) Atoms are indivisible.
(iii) Atoms of a given element are identical.
(iv) Atoms of different elements are different and have different properties.
Which of the postulates is(are) no longer considered valid?
A) (i) and (ii) B) (ii) only C) (ii) and (iii)
D) (iii) only E) (iii) and (iv)
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a.
A. the law of conservation of matterB. the law of multiple proportions
C. the law of constant composition
D. the law of conservation of grams
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b.
A. The second compound must have twice as many oxygen
atoms per carbon atom as the first compound.
B. The second compound must have half as many oxygen
atoms per carbon atom as the first compound.
C. The second compound contains half as many carbon atoms
as the first compound.
D. The first compound contains half as many carbon atoms as
the second compound.
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The Electron
Streams of negatively charged particles were found to
emanate from cathode tubes, causing fluorescence.
J. J. Thomson is credited with their discovery (1897).
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The Electron
Thomson measured the charge/mass ratio ofthe electron to be 1.76 108 coulombs/gram(C/g).
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Millikan Oil-Drop Experiment
Once the charge/mass
ratio of the electron
was known,determination of either
the charge or the mass
of an electron would
yield the other.
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Millikan Oil-Drop Experiment
Robert Millikan
(University of Chicago)
determined the charge
on the electron in
1909.
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Radioactivity
Radioactivity is the spontaneous emission of
radiation by an atom.
It was first observed by Henri Becquerel. Marie and Pierre Curie also studied it.
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Radioactivity
Three types of radiation were discovered byErnest Rutherford: particles
particles
rays
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The Atom, circa 1900
The prevailing theory
was that of the plum
pudding model, putforward by Thomson.
It featured a positive
sphere of matter with
negative electronsimbedded in it.
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Discovery of the Nucleus
Ernest
Rutherford shot
particles at athin sheet of
gold foil and
observed the
pattern of scatterof the particles.
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The Nuclear Atom
Since some particles
were deflected at
large angles,
Thomsons model
could not be correct.
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The Nuclear Atom
Rutherford
postulated a very
small, densenucleus with the
electrons around the
outside of the atom.
Most of the volumeof the atom is empty
space.
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Other Subatomic Particles
Protons were discovered by Rutherford in
1919.
Neutrons were discovered by James
Chadwick in 1932.
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Subatomic Particles
Protons and electrons are the only particles that
have 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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Practice Problems
1) Which statement below correctly describes the responses of alpha, beta, and gamma
radiation to an electric field?
A) Both beta and gamma are deflected in the same direction, while alpha shows no response.
B) Both alpha and gamma are deflected in the same direction, while beta shows no response.
C) Both alpha and beta are deflected in the same direction, while gamma shows no response.
D) Alpha and beta are deflected in opposite directions, while gamma shows no response.
E) Only alpha is deflected, while beta and gamma show no response.
2) The charge on an electron was determined in the __________.
A) cathode ray tube, by J. J. Thompson B) Rutherford gold foil experiment
C) Millikan oil drop experiment D) Dalton atomic theory
E) atomic theory of matter
3) __________-rays consist of fast-moving electrons.
A) Alpha B) Beta C) Gamma
D) X E) none of the above
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Practice Problems4) The gold foil experiment performed in Rutherford's lab __________.
A) confirmed the plum-pudding model of the atom
B) led to the discovery of the atomic nucleus
C) was the basis for Thomson's model of the atom
D) utilized the deflection of beta particles by gold foil
E) proved the law of multiple proportions
5) In the Rutherford nuclear-atom model, __________.
A) the heavy subatomic particles, protons and neutrons, reside in the nucleusB) the three principal subatomic particles (protons, neutrons, and electrons) all have essentially
the same mass
C) the light subatomic particles, protons and neutrons, reside in the nucleus
D) mass is spread essentially uniformly throughout the atom
E) the three principal subatomic particles (protons, neutrons, and electrons) all have essentially
the same mass and mass is spread essentially uniformly throughout the atom
6) Cathode rays are __________.
A) Neutrons B) x-rays C) electrons
D) Protons E) atoms
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Symbols of Elements
Elements are symbolized by one or two
letters.
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Symbols of Elements
All atoms of the same element have the same
number of protons, which is called the atomic
number, Z.
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Symbols of Elements
The mass of an atom in atomic mass units
(amu) is the total number of protons and
neutrons in the atom.
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Isotopes
Isotopes are atoms of the same element with
different masses.
Isotopes have different numbers of neutrons.
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Atomic Mass
Atomic and
molecular masses
can be measuredwith great accuracy
using a mass
spectrometer.
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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.
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Practice Problems1) There are __________ electrons, __________ protons, and __________ neutrons in an atom
of .
A) 132, 132, 54 B) 54, 54, 132 C) 78, 78, 54
D) 54, 54, 78 E) 78, 78, 132
2) An atom of the most common isotope of gold, 197Au, has __________ protons, __________
neutrons, and __________ electrons.
A) 197, 79, 118 B) 118, 79, 39 C) 79, 197, 197
D) 79, 118, 118 E) 79, 118, 79
3) Which combination of protons, neutrons, and electrons is correct for the isotope of copper ,
A) 29 p+, 34 n, 29 e- B) 29 p+, 29 n, 63 e-
C) 63 p+, 29 n, 63 e- D) 34 p+, 29 n, 34 e-
E) 34 p+, 34 n, 29 e-
4) Which isotope has 45 neutrons?
A) Kr B) Br C) Se D) Cl E) Rh
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Practice Problems5) The element X has three naturally occurring isotopes. The isotopic masses (amu) and %
abundances of the isotopes are given in the table below. The average atomic mass of the
element is __________ amu.
6) An unknown element is found to have three naturally occurring isotopes with atomic masses
of 35.9675 (0.337%), 37.9627 (0.063%), and 39.9624 (99.600%). Which of the following is the
unknown element?
A) Ar
B) K
C) Cl
D) Ca
E) None of the above could be the unknown element.
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Periodic Table
The periodic
table is a
systematic catalogof the elements.
Elements are
arranged in order
of atomic number.
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Periodic Table
The rows on the
periodic chart are
periods.
Columns aregroups.
Elements in the
same group have
similar chemical
properties.
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Periodicity
When one looks at the chemical properties of
elements, one notices a repeating pattern ofreactivities.
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Groups
These five groups are known by their names.
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Periodic Table
Nonmetals are
on the right side
of the periodictable (with the
exception of H).
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Periodic Table
Metalloids
border the
stair-step line
(with the
exception of Al,
Po, and At).
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Periodic Table
Metals are on
the left side of
the chart.
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Chemical Formulas
The subscript to the rightof the symbol of an
element tells the number
of atoms of that element
in one molecule of thecompound.
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Chemical Formulas
Molecular compoundsare composed of
molecules and almost
always contain only
nonmetals.
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Diatomic Molecules
These seven elements occur naturallyas molecules containing two atoms:
Hydrogen
Nitrogen
Oxygen
Fluorine
Chlorine Bromine
Iodine
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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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Types of Formulas
Structural formulas show
the order in which atoms are
bonded. Perspective drawings also
show the three-dimensional
array of atoms in a
compound.
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Ions
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.
Anions are negative and are formed by elements
on the right side of the periodic chart.
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Ionic Bonds
Ionic compounds (such as NaCl) aregenerally formed between metals and
nonmetals.
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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 the anion.
The charge on the anion becomes the subscript
on the cation.
If these subscripts are not in the lowest whole-
number ratio, divide them by the greatest common
factor.
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Common Cations
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Common Anions
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Practice Problems
1) There are __________ protons, __________ neutrons, and __________ electrons in 131I-.
2) There are __________ protons, __________ neutrons, and __________ electrons in 238U+5.
3) Which species has 48 electrons?
4) What is the formula of the compound formed between strontium ions and nitrogen ions?
A) SrN B) Sr3N2 C) Sr2N3 D) SrN2 E) SrN3
5) Magnesium reacts with a certain element to form a compound with the general formula MgX.
What would the most likely formula be for the compound formed between potassium and
element X?
A) K2X B) KX2 C) K2X3 D) K2X2 E) KX
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Practice Problems
Which of the formulas below does not represent acompound that actually exists?
a. CaCO3
b. H2O2
c. KMnO4
d. Na2PO
3
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Inorganic Nomenclature
Write the name of the cation.
If the anion is an element, change itsending to -ide; if the anion is a polyatomicion, simply write the name of thepolyatomic ion.
If the cation can have more than onepossible charge, write the charge as aRoman numeral in parentheses.
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Patterns in Oxyanion Nomenclature
When there are two oxyanions involving the
same element:
The one with fewer oxygens ends in -i te. The one with more oxygens ends in -ate.
NO2 : nitrite; SO32 : sulfite
NO3
: nitrate; SO42
: sulfate
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Patterns in Oxyanion Nomenclature
Central atoms on the second row have bond
to at most three oxygens; those on the thirdrow take up to four.
Charges increase as you go from rightto left.
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Patterns in Oxyanion Nomenclature
The one with the second fewest oxygens ends in -i te.
ClO2 : chlorite
The one with the second most oxygens ends in -ate.
ClO3
: chlorate
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Patterns in Oxyanion Nomenclature
The one with the fewest oxygens has the prefixhypo- and ends in -i te.
ClO: hypochlorite
The one with the most oxygens has the prefix
per- and ends in -ate.
ClO4: perchlorate
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Acid Nomenclature
If the anion in the acid
ends in -ide, change
the ending to -ic acid
and add the prefixhydro- .
HCl: hydrochloric acid
HBr: hydrobromic acid
HI: hydroiodic acid
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Acid Nomenclature
If the anion in the acid
ends in -i te, change the
ending to -ous acid.
HClO: hypochlorous acid HClO2: chlorous acid
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Acid Nomenclature
If the anion in the acid
ends in -ate, change
the ending to -ic acid.
HClO3: chloric acid HClO4: perchloric acid
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Nomenclature of Binary Compounds
The less electronegativeatom is usually listed first.
A prefix is used to denotethe number of atoms ofeach element in thecompound (mono- is notused on the first element
listed, however) .
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Nomenclature of Binary Compounds
The ending on the more
electronegative element
is changed to -ide.
CO2: carbon dioxide
CCl4: carbon tetrachloride
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Nomenclature of Binary Compounds
If the prefix ends with aoro and the name of theelement begins with a
vowel, the twosuccessive vowels areoften elided into one.
N2O5: dinitrogen pentoxide
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Nomenclature of Organic Compounds
Organic chemistry is the study of carbon.
Organic chemistry has its own system ofnomenclature.
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Nomenclature of Organic Compounds
The simplest hydrocarbons (compoundscontaining only carbon and hydrogen) arealkanes.
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Nomenclature of Organic Compounds
The first part of the names just listed
correspond to the number of carbons(meth-= 1, eth-= 2, prop-= 3, etc.).
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Nomenclature of Organic Compounds
When a hydrogen in an alkane is replaced with
something else (a functional group, like -OH in
the compounds above), the name is derived fromthe name of the alkane.
The ending denotes the type of compound.
An alcohol ends in -ol
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