Fundamentals of General, Organic, and
Biological Chemistry
5th Edition
Chapter Three
Atoms and the Periodic
Table
James E. Mayhugh
Oklahoma City University
2007 Prentice Hall, Inc.
Outline
3.1 Atomic Theory
3.2 Elements and Atomic Number
3.3 Isotopes and Atomic Weight
3.4 The Periodic Table
3.5 Some Characteristics of Different Groups
3.6 Electronic Structure of Atoms
3.7 Electron Configurations
3.8 Electron Configurations and the Periodic Table
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3.1 Atomic Theory
Chemistry is founded on four fundamental
assumptions about atoms and matter, which together
make up modern atomic theory:
1. All matter is composed of atoms.
2. The atoms of a given element differ from the
atoms of all other elements.
3. Chemical compounds consist of atoms combined
in specific ratios.
4. Chemical reactions change only the way the
atoms are combined in compounds; the atoms
themselves are unchanged.
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► Atoms are composed of tiny subatomic particles
called protons, neutrons, and electrons.
► The masses of atoms and their constituent
subatomic particles are very small when measured
in grams. Atomic masses are expressed on a
relative mass scale. One atom is assigned a mass,
and all others are measured relative to it.
► The basis for the relative atomic mass scale is an
atom of carbon that contains 6 protons and 6
neutrons. This carbon atom is assigned a mass of
exactly 12 atomic mass units (amu).
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►Both protons and neutrons have a mass close to one
amu.
►Electrons are 1836 times lighter than protons and
neutrons.
►Protons and electrons have electrical charges that
are equal in magnitude but opposite in sign.
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► The protons and neutrons are packed closely
together in a dense core called the nucleus.
Surrounding the nucleus, the electrons move
about rapidly through a large volume of space.
►The relative size
of a nucleus in
an atom is the
same as that of a
pea in the
middle of this
stadium.
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► Diameter of a nucleus is only about 10-15 m.
► Diameter of an atom is only about 10-10 m.
The atom is
100,000 times larger
then the center
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► The structure of the atom is determined by
interplay of different forces.
► Opposite electrical charges attract each other,
like charges repel each other.
► Protons and neutrons in the nucleus are held
together by the nuclear strong force.
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3.2 Element and Atomic Number
►Atomic number (Z): The number of protons in
each atom of an element. All atoms of a particular
element have the same number of protons in the
nucleus.
►Atoms are neutral overall and have no net charge
because the number of positively charged protons
and the number of negatively charged electrons are
the same in each atom.
►Mass number (A): The total number of protons
and neutrons in an atom.
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3.3 Isotopes and Atomic Weight
Isotopes: Atoms with identical atomic numbers (Z)
but different mass numbers (A) are called isotopes.
Protium, deuterium, and tritium are three isotopes
of the element hydrogen.
►
Hydrogen, the most abundant hydrogen
isotope, has one proton and no neutrons
(Z=1, A=1)
►
Deuterium , this heavy hydrogen isotope has
one proton and one neutron (Z=1, A=2)
►
Tritium, this radioactive hydrogen isotope has
one proton and two neutrons (Z=1, A=3).
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Isotopes of Hydrogen
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A specific isotope is represented by showing its mass
number (A) as a superscript and its atomic number
(Z) as a subscript in front of the atomic symbol. For
example, the symbol for tritium is:
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Learning Check
How many protons, neutrons, and electrons are
in a carbon-13 atom?
6 protons, 7 neutrons, 6 electrons
What is the identity of an element with 42
protons/electrons and 53 neutrons? Write
the complete symbol.
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Learning check
Write the symbol for copper-63.
How many neutrons are in copper-63?
63 = p+ + n°
63 - 29 p+ = 34 n°
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How many protons, electrons, and neutrons are in
the atom shown below?
235
92
U
1.
2.
3.
4.
92p, 92e, 43n
92p, 43e, 235n
92p, 92e, 235n
235p, 235e, 43n
How many protons, electrons, and neutrons are in
the atom shown below?
235
92
U
1.
2.
3.
4.
92p, 92e, 143n
92p, 43e, 235n
92p, 92e, 235n
235p, 235e, 143n
Atomic weight: The weighted average mass of an
element’s atoms in a large sample that includes all
the naturally occurring isotopes of that atom.
To calculate the atomic weight of an element, the
individual mass and the percent abundance of each
naturally occurring isotope must be known.
Atomic weight = (isotope abundance)*(isotope
mass)
The Greek symbol  indicates the summation of
terms over all naturally occurring isotopes.
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Chapter Seven
Learning check
Copper has two naturally occurring isotopes. A
typical sample consists of 69.17% Cu-63
(62.939598 amu) and 30.83% Cu-65
(64.927793 amu). Calculate the atomic mass
of copper.
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3.4 The Periodic Table
► Beginning at the upper left corner of the periodic
table, elements are arranged by increasing atomic
number into seven horizontal rows, called periods,
and 18 vertical columns, called groups.
► The elements in a given group have similar
chemical properties. Lithium, sodium, potassium,
and other elements in group 1A (or 1) have similar
properties. Similarly, chlorine, bromine, iodine,
and other elements in group 7A (or 17) behave
similarly.
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The table has 114 boxes, each of which tells the
symbol, atomic number, and atomic weight of an
element.
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All seven periods do not contain the same number
of elements.
► The first period contains only 2 elements.
► The second and third periods each contain 8
elements.
► The fourth and fifth periods each contain 18
elements.
► The sixth period contains 32 elements.
► The seventh period, still incomplete, contains
27 elements.
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Learning Check
Who is the element in Period 2, Group 14?
Carbon
Who is the element in Period 5, Group 2?
Strontium
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The groups on the periodic table are divided into three
main categories.
►Main Groups: The two groups on the far left (1-2)
and the six on the far right (13-18) are the main
groups.
►Transition Metal Groups: Elements in the groups
numbered 3 through 12.
►Inner Transition Metal Groups: The 14 groups
shown at the bottom of the table that are not
numbered containing the Lanthanides and the
Actinides.
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3.5 Characteristics of Different Groups
Group 1A or 1 Alkali metals:
► Li, Na, K, Rb, Cs, and Fr
► Shiny, soft, and low
melting point metals
► All react rapidly with water
to form flammable H2 gas
and alkaline or basic
solutions.
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► Group 2A or 2 Alkaline
earth metals:
► Be, Mg, Ca, Sr, Ba, and Ra
► Lustrous, silvery metals
► React with O2
► They are less reactive to
water than the alkali
metals.
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Group 7A or 17 Halogens:
►F, Cl, Br, I, and At
►Colorful and corrosive
nonmetals
►All are found in nature in
combination with other
elements, such as with
sodium in sodium
chloride (NaCl).
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Group 8A or 18 Noble gases:
► He, Ne, Ar, Kr, Xe, and Rn
► Colorless gases
► Very low chemical reactivity
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A graph of atomic size versus atomic number shows
a periodic rise-and-fall pattern. The maxima occur
for atoms of the group 1A elements; the minima
occur for atoms of the group 7A elements.
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3. 6 Electronic Structure of Atoms
Quantum mechanical model of atomic structure:
► The electrons in an atom are grouped around the
nucleus into shells, roughly like the layers in an
onion.
► The farther a shell is from the nucleus, the larger it
is, the more electrons it can hold, and the higher
the energies of those electrons.
► The smallest shell closest to the nucleus is labeled
shell 1, the next one is shell 2, and so on.
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The electromagnetic spectrum
Robert Hooke in the 1660’s publishes the wave
behavior of light
Muslim Ibn al-Haitham (c. 965-1040), 1st optic theory
It has known by 1870 that elements, when
excited, produce distinct lines
These distinct lines are the shells in an atom.
When an electron moves from one color to the
next it is moving from one shell to the next
Stairs are quantized because they change height in
discrete amounts. A ramp, by contrast, is not
quantized because it changes height continuously.
When things
are quantized
(like electrons)
they are
restricted to
having only
certain values;
or color for an
electron on the
previous slide.
Excited Atoms Emit Light
The lines are thought to
come from an excited
electron emitting an photon
after coming back to it’s
ground state (bottom of stair
case).
n = a shell, so n = 1 is closest
to the nucleus. The atom
appears like an onion.
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The electron climbs (after being
excited) then falls to it’s original spot
in the ladder (onion layer), giving off a
photon on the way back down.
Quantum Mechanics
Niels Bohr (pronounced Niel) calculates the first
emission line spectrum—a great
accomplishment, and receives a Nobel in 1922
Bohr’s model is not perfect, it only works for 1
electron atoms like H, He+, Li2+
The problem is Bohr does not account for
Einstein's findings
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Quantum Mechanics
Albert Einstein shows
the photoelectric
effect, proving that
light behaves like a
particle. He receives
his only Nobel for the
photoelectric effect in
1921
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Quantum Mechanics
Louis de Broglie (in 1924) proposed that all
moving objects have wave properties. He
combines the work of Bohr and Einstein in the
a formula called the “wave-nature of matter.”
Nobel in 1929
Werner Heisenberg’s proposes the uncertainty
principle: a relation that states the
uncertainty in position and the uncertainty in
momentum of a particle, for very small
particles. Nobel in Chapter
1932
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Three
Quantum Mechanics
Erwin Schrödinger defined this probability in a
mathematical expression called a wave
function, denoted y (psi). Nobel in 1933.
The probability of finding a particle in a region
of space is defined by y2.
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Quantum Mechanics
Erwin Schrödinger’s y2 computerized probability of
finding an electron in a region of space !
3rd shell
2nd shell
1st shell
The outer Onion
The inner parts of onions
► Within the shells, electrons are further
grouped into subshells of four different
types, identified as s, p, d, and f in order of
increasing energy.
► A shell has a number of subshells equal to
its shell number.
► The first shell has only an s subshell; the
second shell has an s and a p subshell; the
third shell has an s, a p, and a d subshell,
and so on.
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► Within each subshell, electrons are further grouped
into orbitals, regions of space within an atom
where the specific electrons are more likely to be
found.
► The number of orbitals within a subshell increases
as the odd numbers.
► An s subshell has 1 orbital, a p has 3, a d has 5, and
so on.
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Different orbitals have different shapes. Orbitals in s
subshells are spherical (a), while orbitals in p
subshells are roughly dumbbell shaped (b).
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► Any orbital can hold a maximum of 2 electrons.
► The first shell has one 1s orbital and holds 2
electrons.
► The second shell can hold 8 electrons, 2 in a 2s
orbital, and 6 in three 2p orbitals.
► The third shell can hold 18 electrons, 2 in a 3s
orbital, 6 in three 3p orbitals, and 10 in five 3d
orbitals, and so on.
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The overall electron distribution within an atom is
summarized in Table 3.2 below.
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3.7 Electron Configurations
Electron Configuration: The exact arrangement
of electrons in atom’s shells and subshells. Rules
to predict electron configuration:
1. Electrons occupy the lowest energy orbitals
available first.
2. Each orbital can hold only two electrons, which
must be of opposite spin.
3. If two or more orbitals have the same energy,
each orbital gets one electron before any orbital
gets two.
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Order of orbital energy
levels:
►Electrons fill orbitals
from the lowest-energy
orbitals upward.
► Lower numbered shells
fill before higher numbered
shells at first.
►Some overlap in energy
levels occurs starting with
shell 3 and 4.
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►Electron configurations are described by writing the
shell number and subshell letter in order of increasing
energy. The number of electrons actually occupying
each subshell is indicated by a superscript.
►Orbital Box Notation: A graphic representation can
be made by indicating each orbital as a line and each
electron as an arrow. The head of the arrow indicates
the electron spin.
►A shorthand using noble gas configurations is very
useful for large atoms.
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These are the electron configurations for B - N
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These are the electron configurations for O - Ne
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Who is this?
Who is this?
Ga
Who is this?
Ni
3.8 Electron Configuration and the
Periodic table
Valence shell: Outermost, highest energy shell of an
atom.
Valence electrons: An electron in an outermost shell
of an atom. These electrons are loosely held, they are
most important in determining an element’s
properties.
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►The periodic table can be divided into four regions or
blocks, of elements according to the subshells that
are last to fill, s, p, d, or f.
►Beginning at the top left corner of the periodic table,
the first row contains only two elements, H and He.
The 1s subshell is being filled here.
►The second row begins with two s-block elements (Li
and Be) and continues with six p-block elements (B
through Ne), so electrons fill the next available s
orbital (2s) and then the first available p orbitals (2p).
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►The third row is similar to the second row, so the 3s
and 3p orbitals are filled next.
►The fourth row again starts with two s-block
elements (K and Ca) but is then followed by ten dblock elements (Sc through Zn) and six p-block
elements (Ga through Kr). Thus, the order of orbital
filling is 4s followed by the first available d orbitals
(3d) followed by 4p.
► Continuing through successive rows of the periodic
table provides a visual method to recall the entire
filling order.
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Visual method to recall the order of orbital filling.
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Learning check
Who is:
1s22s22p63s23p2
[Ar]3d104s24p4
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Si
Se
Ar
Br
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Chapter Summary
►An atom is the smallest unit of an element that
maintains the properties of the element.
► Atoms are made up of protons, neutrons, and
electrons. Protons have a positive charge, neutrons are
neutral, and electrons have a negative charge.
► Protons and neutrons are present in a dense,
positively charged region called the nucleus. Electrons
are a relatively large distance away from the nucleus.
►The number of protons an element contains is called
the atomic number (Z). The total number of protons
plus neutrons in an atom is called the mass number
(A).
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Chapter Three
Chapter Summary Cont.
►Atoms with identical numbers of protons and
electrons but different numbers of neutrons are called
isotopes.
►The atomic weight of an element is the weighted
average mass of the element’s naturally occurring
isotopes measured in atomic mass units (amu).
►Elements are organized into the periodic table,
consisting of 7 rows, or periods, and 18 columns, or
groups.
►Elements in the same group have the same number
of valence electrons in their outermost shell.
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Chapter Summary Cont.
►Electrons in an atom are grouped into layers, or
shells. In each shell, electrons are grouped into
subshells, and each subshell into orbitals.
►s orbitals are spherical, and p orbitals are dumbbell
shaped.
►Each orbital can hold 2 electrons. Each shell can hold
a number of electrons equal to 2 times the shell
number squared. The first shell can hold 2, the second
shell can hold 8, the third shell can hold 18, and so on.
►The electron configuration of an element is
predicted by assigning the element’s electrons into
orbitals, beginning with the lowest-energy orbital.
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End of Chapter 3
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