Chapter 4 Chemical Foundations: Elements, Atoms, and Ions
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Atomic Structure
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Objectives Explain early models of the atom Differentiate
between three types of subatomic particles Define isotope and
calculate the atomic mass
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Sections 4.1 Defining the Atom 4.2 Structure of the Nuclear
Atom 4.3 Distinguishing Between Atoms
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4.1 Defining the Atom Vocabulary - Atom - Daltons atomic theory
Atom is the smallest particle of an element that retains its
identity in a chemical reaction. Daltons atomic theory- the first
theory to relate chemical changes to events at the atomic
level
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Experiencing Atoms Atoms are incredibly small, yet they compose
everything Atoms are the pieces of elements Properties of the atoms
determine the properties of the elements If every atom within a
pebble were the size of the pebble itself, then the pebble would be
larger than Mt. Everest (~29,000 ft)
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Early Models of the Atom Democritus The Greek philosopher
Democritus (460 BC 370 BC) was among the first to suggest the
existence of atoms. He believed that atoms were indivisible and
indestructible
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Early Models of the Atom John Dalton (1766-1844) Daltons Atomic
Theory - By using experimental methods, Dalton transformed
Democrituss ideas on atoms into a scientific theory.
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Daltons Atomic Theory 1. All elements are composed of tiny
indivisible particles called atoms. 2. Atoms of the same element
are identical. The atoms of any one element are different from
those of any other element.
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3. Atoms of different elements can physically mix together or
can chemically combine in simple whole-number ratios to form
compounds. 4. Chemical reactions occur when atoms are separated,
joined, or rearranged. Atoms of one element are never changed into
atoms of another element in a chemical reaction.
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What instruments are used to observe individual atoms? Despite
their small size, individual atoms are observable with instruments
such as scanning tunneling microscopes. Sizing up the Atom
http://www.hk-phy.org/atomic_world/stm/stm01_e.html
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4.2 Structure of the Nuclear Atom Electron a negatively charged
subatomic particle Cathode ray- a stream of electrons produced at
the negative electrode (cathode) of a tube containing a gas at low
pressure Proton a positively charged subatomic particle found in
the nucleus of an atom Neutron a subatomic particle with no charge
and a mass of 1 amu Nucleus- the tiny, dense central portion of an
atom, composed of protons and neutrons Vocabulary - Electron -
Cathode ray - Proton - Neutron - Nucleus
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Subatomic Particles 4.2
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Electrons English physicist J.J. Thomson discovered the
electron (1897) Electrons are negatively charged subatomic
particles. Cathode ray tube Thomson performed experiments that
involved passing electric current through gases at low
pressure.
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Electrons The U.S. physicist Robert A. Millikan (18681953)
carried out experiments to find the quantity of an electrons
charge. Using this charge and Thomsons charge-to-mass ratio of an
electron, Millikan calculated an electrons mass. An electron has
one unit of negative charge, and its mass is 1/1840 the mass of a
hydrogen atom.
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Protons Eugen Goldstein (18501930) Observed a cathode-ray tube
and found rays traveling in the direction opposite to that of the
cathode rays. - He concluded that they were composed of positive
particles. - Such positively charged subatomic particles are called
protons.
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Neutrons Physicist James Chadwick (18911974) Confirmed the
existence of another subatomic particle: the neutron. Neutrons are
subatomic particles with no charge but with a mass nearly equal to
that of a proton.
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Subatomic Particles Table 4.1 summarizes the properties of
electrons, protons, and neutrons. 4.2
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Atomic Nucleus J.J. Thompson and others supposed the atom was
filled with positively charged material and the electrons were
evenly distributed throughout. Plum pudding model Plum pudding
model - This model of the atom turned out to be short-lived,
however, due to the work of Ernest Rutherford (18711937).
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The Atomic Nucleus Ernest Rutherfords Portrait 4.2
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Ernest Rutherford Discovered the nucleus (1911) Stated protons
were inside of the nucleus Gold-Foil Experiment Radioactive
particles shot through gold foil - A majority of particles passed
straight through foil - A small fraction of particles bounced off
gold foil at large angles or bounced straight back
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The Atomic Nucleus Rutherfords Gold-Foil Experiment 4.2
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The Atomic Nucleus In the nuclear atom, the protons and
neutrons are located in the nucleus. The electrons are distributed
around the nucleus and occupy almost all the volume of the atom.
4.2
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4.3 Distinguishing Among Atoms Vocabulary - Atomic number -
Mass number - Isotopes - Atomic Mass Unit - Atomic mass - Periodic
table - Period - Group Atomic number the number of protons in the
nucleus of an atom of an element Mass number- the total number of
protons and neutrons in the nucleus of an atom Isotopes- atoms of
the same element that have the same atomic number but different
atomic masses due to a different number of neutrons Atomic mass
unit- a unit of mass equal to one-twelfth the mass of a carbon-12
atom Atomic mass- the weighted average of the masses of the
isotopes of an element Periodic table- an arrangement of elements
in which the elements are separated into groups based on a set of
repeating properties Period- a horizontal row of elements in the
periodic table Group- a vertical column of elements in the periodic
table; the constituent elements of a group have similar chemical
and physical properties
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Copyright Pearson Education, Inc., or its affiliates. All
Rights Reserved. Just as there are many types of dogs, atoms come
in different varieties too. How can there be different varieties of
atoms?
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Atomic Number *Elements are different because they contain
different numbers of protons. An elements atomic number is the
number of protons in the nucleus of an atom of that element. The
atomic number identifies an element.
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Copyright Pearson Education, Inc., or its affiliates. All
Rights Reserved. For each element listed in the table below, the
number of protons equals the number of electrons. (Protons =
Electrons) Interpret Data Atoms of the First Ten Elements
NameSymbolAtomic number ProtonsNeutronsMass number Electrons
HydrogenH11011 HeliumHe22242 LithiumLi33473 BerylliumBe44594
BoronB556115 CarbonC666126 NitrogenN777147 OxygenO888168
FluorineF9910199 NeonNe10 2010
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Understanding Atomic Number The element nitrogen (N) has an
atomic number of 7. How many protons and electrons are in a neutral
nitrogen atom? How many protons and electrons are in a Krypton
atom?
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Mass Number The total number of protons and neutrons in an atom
is called the mass number. The number of neutrons in an atom is the
difference between the mass number and atomic number.
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Mass Number Au is the chemical symbol for gold. 4.3 The atomic
number is the subscript. The mass number is the superscript.
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Symbols Find the - number of protons - number of neutrons -
number of electrons - Atomic number - Mass Number - Name Na 24
11
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4.3 Isotopes Isotopes are atoms that have the same number of
protons but different numbers of neutrons. Because isotopes of an
element have different numbers of neutrons, they also have
different mass numbers.
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Isotopes 2 isotopes of Carbon: - C 12 - C -14
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Isotopes Despite these differences, isotopes are chemically
alike because they have identical numbers of protons and electrons.
4.3
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Isotopes For example, hydrogen has 3 isotopes: Note that the
correct way to write an isotopes is to write the name, followed by
the mass number. IsotopeProtonNeutronElectron Hydrogen-1 1 0 1
Hydrogen-2 1 1 1 Hydrogen-3 1 2 1
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Isotopes & Their Uses The tritium content of ground water
is used to discover the source of the water, for example, in
municipal water or the source of the steam from a volcano.
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Isotopes & Their Uses Bone scans with radioactive
technetium-99.
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Copyright Pearson Education, Inc., or its affiliates. All
Rights Reserved. Why are atoms with different numbers of neutrons
still considered to be the same element? Despite differences in the
number of neutrons, isotopes are chemically alike. They have
identical numbers of protons and electrons, which determine
chemical behavior.
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Learning Check An atom has 14 protons and 20 neutrons. A.Its
atomic number is 1) 142) 163) 34 B. Its mass number is 1) 142) 163)
34 C. The element is 1) Si2) Ca3) Se D.Another isotope of this
element is 1) 34 X 2) 34 X 3) 36 X 16 14 14
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Atomic Mass How do you calculate the atomic mass of an element?
4.3
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Atomic Mass An atomic mass unit (amu) is defined as one twelfth
of the mass of a carbon-12 atom. It is more useful to compare atoms
using a reference isotope The mass listed in the periodic table is
the average atomic mass The atomic mass of an element is a weighted
average mass of the atoms in a naturally occurring sample of the
element. 4.3
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Atomic Mass To calculate the atomic mass of an element,
multiply the mass of each isotope by its natural abundance,
expressed as a decimal, and then add the products. 4.3
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Atomic Mass Carbon has two stable isotopes: carbon-12, which
has a natural abundance of 98.89 percent, and carbon-13, which has
a natural abundance of 1.11 percent. The mass of carbon-12 is
12.000 amu; the mass of carbon-13 is 13.003 amu. The atomic mass of
carbon is calculated as follows: Atomic mass of carbon = (12.000
amu x 0.9889) + 13.003 amu x 0.0111) = (11.867 amu) + (0.144 amu) =
12.011 amu
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Copyright Pearson Education, Inc., or its affiliats. All Rights
Reserved. The mass each isotope contributes to the elements atomic
mass can be calculated by multiplying the isotopes mass by its
relative abundance. The atomic mass of the element is the sum of
these products. Analyze List the knowns and the unknown. 1 atomic
mass of X = ? KNOWNS UNKNOWN Isotope 10 X: mass = 10.012 amu
relative abundance = 19.91% = 0.1991 Isotope 11 X: mass = 11.009
amu relative abundance = 80.09% = 0.8009
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Use the atomic mass and the decimal form of the percent
abundance to find the mass contributed by each isotope. for 10 X:
10.012 amu x 0.1991 = 1.993 amu for 11 X: 11.009 amu x 0.8009 =
8.817 amu Calculate Solve for the unknowns. 2
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Add the atomic mass contributions for all the isotopes.
Calculate Solve for the unknowns. 2 For element X, atomic mass =
1.953 amu + 8.817 amu = 10.810 amu
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Evaluate Does the result make sense? 3 The calculated value is
closer to the mass of the more abundant isotope, as would be
expected.
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Copyright Pearson Education, Inc., or its affiliates. All
Rights Reserved. Key Concepts Elements are different because they
contain different numbers of protons. Because isotopes of an
element have different numbers of neutrons, they also have
different mass numbers. To calculate the atomic mass of an element,
multiply the mass of each isotope by its natural abundance,
expressed as a decimal, and then add the products.
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Periodic Table-A Preview
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Periodic Table A periodic table is an arrangement of elements
in which the elements are separated into groups based on a set of
repeating properties It allows you to compare the properties of one
element to another element. Period- a horizontal row of elements in
the periodic table Group- a vertical column of elements in the
periodic table; the constituent elements of a group have similar
chemical and physical properties *Elements are listed in order of
increasing atomic number, from left to right and top to
bottom.
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ATOMIC COMPOSITION Protons (p + ) Protons (p + ) + electrical
charge + electrical charge mass = 1.672623 x 10 -24 g mass =
1.672623 x 10 -24 g relative mass = 1.007 atomic mass units (amu)
but we can round to 1 relative mass = 1.007 atomic mass units (amu)
but we can round to 1 Electrons (e - ) Electrons (e - ) negative
electrical charge negative electrical charge relative mass = 0.0005
amu but we can round to 0 relative mass = 0.0005 amu but we can
round to 0 Neutrons (n o ) Neutrons (n o ) no electrical charge no
electrical charge mass = 1.009 amu but we can round to 1 mass =
1.009 amu but we can round to 1
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IONS IONS are atoms or groups of atoms with a positive or
negative charge. IONS are atoms or groups of atoms with a positive
or negative charge. Taking away an electron from an atom gives a
CATION with a positive charge Taking away an electron from an atom
gives a CATION with a positive charge Adding an electron to an atom
gives an ANION with a negative charge. Adding an electron to an
atom gives an ANION with a negative charge. To tell the difference
between an atom and an ion, look to see if there is a charge in the
superscript! Examples: Na + Ca +2 I - O -2 To tell the difference
between an atom and an ion, look to see if there is a charge in the
superscript! Examples: Na + Ca +2 I - O -2 Na Ca I O Na Ca I O
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PREDICTING ION CHARGES In general metals (Mg) lose electrons
---> cations metals (Mg) lose electrons ---> cations
nonmetals (F) gain electrons ---> anions nonmetals (F) gain
electrons ---> anions
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Learning Check Counting State the number of protons, neutrons,
and electrons in each of these ions. 39 K + 16 O -241 Ca +2 198 20
#p + ___________________ #n o ___________________ #e -
___________________
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One Last Learning Check Write the nuclear symbol form for the
following atoms or ions: A. 8 p +, 8 n, 8 e - ___________ B.17p +,
20n, 17e - ___________ C. 47p +, 60 n, 46 e - ___________
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Charges on Common Ions -2-3 +1 +2 By losing or gaining e-, atom
has same number of e-s as nearest Group 8A atom.
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Regions of the Periodic Table
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Group 1A: Alkali Metals Cutting sodium metal Reaction of
potassium + H 2 O
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Magnesium Magnesium oxide Group 2A: Alkaline Earth Metals
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Group 7A: The Halogens (salt makers) F, Cl, Br, I, At