Chapter 3
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Atoms and Elements
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Classifying Matter
Elements and Symbols
Periodic Table
Atomic Structure
Atomic Mass
Electronic Structure
Periodic Trends
Classification of Matter
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Pure Substance = matter that has a
fixed or definite composition.

Both elements and compounds are
examples of pure substances.
Elements are composed of only one type of
atom.
Compounds are composed of two or more
elements, but always in the same ratio.
Classification of Matter
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Compounds may be broken down into
their elements through chemical
reactions.
Elements can not be decomposed into
simpler substances via chemical
reactions.
Compounds can not be broken down into
simpler substances via physical processes
like boiling or filtering.
Classification of Matter
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Much of the matter we encounter is a
mixture.
A mixture contains two or more pure
substances that are physically mixed
together.
Physical processes can be used to
separate mixtures.
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ex) iron fillings and sand can be separated by
using a magnet.
ex) sugar and water can be separated by
evaporating off all of the water.
Classification of Matter
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Mixtures can be classified as either
homogeneous or heterogeneous.
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Homogeneous – means that it is uniform
throughout. Air, salt water, and brass are
examples of homogeneous mixtures.
Heterogeneous – means that it is NOT
uniform throughout. A rock, a chocolate chip
cookie, and a can of soda are examples of
heterogeneous mixtures.
Learning Check
Identify each of the following as a pure substance
or a mixture.
A. pasta and tomato sauce
B. aluminum foil
C. helium
D. air
Learning Check
Identify each of the following as a homogeneous or
heterogeneous mixture:
A. hot fudge sundae
B. shampoo
C. sugar water
D. peach pie
Elements and Symbols
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All matter consists of primary substances
called elements.
There are many different types of
elements.
About 112 different elements are known.
Only 88 occur naturally with the rest
produced artificially through nuclear
reactions (Ch. 9).
Elements & Symbols
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Elements cannot be decomposed into
simpler substances.
Elements are the building blocks of all
substances.
The elements are typically denoted with
either a one or two letter designation
usually related to the English name or the
older Latin name.
Elements & Symbols
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The abbreviations for each element are
often called its chemical symbol.
One letter symbols are always capitalized.
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C = carbon, N = nitrogen
Two letter symbols always have the first
letter capitalized with the second one
being lowercase.
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Co = cobalt (CO is the compound carbon
monoxide!)
Cl = chlorine
Latin based symbols
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Some elements have symbols based
on their Latin names because they
were known to the ancient Greeks.
Na (sodium) from natrium
 Pb (lead) from plumbum
 Fe (iron) from ferrum
 K (potassium) from kalium
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Elements Essential to Life
Element
Oxygen
Where Found
Water, carbohydrates, fats, proteins
Carbon
Hydrogen
Nitrogen
Carbohydrates, fats, proteins
Water, carbohydrates, proteins
Proteins, DNA, RNA
Calcium
Phosphorus
Potassium
Bones, teeth
Bones, teeth, DNA, RNA
Inside cells (nerve impulses)
Sulfur
Sodium
Some amino acids
Body fluids (electrolyte)
Elements Essential to Life
Element
Magnesium
Chlorine
Iron
Where Found
Inside cells
Outside cells (electrolyte)
Hemoglobin (blood)
Copper
Zinc
Enzymes
Metabolism, enzymes, energy production
Manganese
Iodine
Fluorine
Enzymes
Thyroid regulation
Teeth
Cobalt
Selenium
Enzymes
Antioxidant, ???
Physical Properties
Characteristics of a substance that
can be observed or measured
without affecting the identity of that
substance.
 Examples include:
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Color, odor, taste, appearance, density,
melting point, and many more.
Physical Properties of
Elements
Some physical properties of
Copper are:
Color
Red-orange
Luster
Very shiny
Melting point
1083°C
Boiling point
2567°C
Conduction of electricity
Excellent
Conduction of heat
Excellent
The Periodic Table
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Dmitri Mendeleev was the first to arrange
the elements in a fashion that showed
repeating patterns.
This arrangement is called the periodic
chart that we use today.
You will receive a periodic chart and mark
down the groups, periods, metal, nonmetal, metalloid designations as well as
main and transition areas on your chart.
The Elements
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Properties of the Metals
metals are found to the left and below
the line that separates the elements.
 metals are shiny solids (except Hg)
 metals are ductile and malleable
(shaped into wires or thin sheets)
 metals are excellent conductors of both
heat and electricity.
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The Elements
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Properties of the Non-metals
non-metals are found to the right and
above the line the separates the
elements.
 non-metals are not shiny, rather those
that are solids are dull in color.
 non-metals are poor conductors.
 many non-metals are gases at room
temperature.
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The Elements
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Properties of the Metalloids
metalloids are the elements that occur
along the line that separate the
elements.
 have properties that are in between
that of metals and non-metals.
 metalloids are semi-conductors.
 table 3.6 (p. 83) compares a metal,
non-metal, and a metalloid.
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Groups with Special Names
Learning Check
Identify the element described by the following.
A. Group 7A, Period 4
1) Br
2) Cl
3) Mn
B. Group 2A, Period 3
1) beryllium 2) boron
3) magnesium
C. Group 5A, Period 2
1) phosphorus
2) arsenic 3) nitrogen
Learning Check
Match the elements to the description.
A. Metals in Group 4A
1) Sn, Pb
2) C, Si
3) C, Si, Ge, Sn
B. Nonmetals in Group 5A
1) As, Sb, Bi
2) N, P
3) N, P, As, Sb
C. Metalloids in Group 4A
1) C, Si, Ge,
2) Si, Ge
3) Si, Ge, Sn, Pb
The Atom
An atom is the smallest particle of
an element that retains the
characteristics of that element.
 Atoms are extremely small – they
cannot be seen.
 John Dalton, theorized the existence
of atoms in 1808.
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Dalton’s Atomic Theory
1.
2.
3.
4.
All matter is made up of tiny particles called
atoms.
All atoms of a given element are similar to one
another; atoms of different elements are
different from each other.
Atoms of two or more different elements
combine to form compounds.
A chemical reaction involves the
rearrangement of atoms into new
combinations. Atoms are never created nor
destroyed in a chemical reaction.
Parts of an Atom
Experiments performed around the
turn of the previous century
(~1900), showed that atoms were
made of several types of particles –
collectively referred to as subatomic
particles.
 These experiments showed that
three types of particles were present
in an atom.
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The Three Particles
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A proton has a +1 charge and an
approximate mass of 1 amu.
Note: an atomic mass unit (amu) is equal
to 1/12 of the mass of a Carbon atom
with 6 protons and 6 neutrons.
A neutron has no charge, but does have a
mass of about 1 amu.
An electron has a –1 charge and a mass
so small that we usually say that it
weighs 0 amu.
Structure of the Atom
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Ernest Rutherford performed an experiment
called the “Gold Foil” experiment in 1911.
He used an alpha particle (2P + 2N) source and
fired them at a piece of very thin gold foil.
He expected all of the particles to pass straight
through. However, some were deflected and
some were even reflected backwards.
In Rutherford’s words, it was as if he had shot a
cannonball at a piece of tissue paper and have it
bounce backwards.
Nuclear Model of the Atom
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Only 1 in 8000 alpha particles is scattered.
Scattering occurs when an alpha particle
encounters a gold nuclei.
A nucleus is very small and contains both the
protons and the neutrons. Thus, it contains
almost all of the mass of an atom.
This very dense center is surrounded by the
electron cloud, which is occupied by the fast
moving electrons.
Thus, an atom is MAINLY EMPTY SPACE.
Nuclear Model of the Atom
Atomic Number & Mass
Number
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All atoms of the same element have the
same number of protons.
This distinguishes one element from
another.
The number of protons is also called the
atomic number.
This is always the integer found on the
periodic chart with each chemical symbol.
Atomic Number & Mass
Number
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Atoms are electrically neutral. Thus, each
element must have an equal number of
protons and electrons.
The mass number of an atom is equal to
the sum total of the protons and neutrons
in the nucleus.
Mass number and atomic weight (found
on the periodic chart) are NOT the same
thing.
Study Check
Name
Symbol Atomic # Mass #
Carbon
#P
#N #e
12
N
8
26
30
Isotopes and Atomic Mass
All atoms of one element have the
same number of protons.
 But, they can have different
numbers of neutrons, and hence, a
different mass number.
 These different versions of atoms
from one element are called
isotopes.
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Isotopic Symbols
Use the chemical symbol, atomic
number (Z), and mass number (A)
as seen below.
 Can also list symbol followed by
mass number.
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A
Z
X or X - A
16
8
O or O - 16
Atomic Mass
The masses found for each element
on the periodic chart are the
weighted average of all the known
isotopes for that element.
Example: Chlorine has only two
known isotopes – Cl-35 and Cl-37.
Cl-35 is found 75.5% of the time
and Cl-37 is found 24.5% of the
time.
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Isotope Mass X
Contribution
(approximate)
mass
Percent
to total
35 amu
amu
X
0.755
37 amu
Totals
X
0.245
1.000
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=
=
26.4
= 9.1 amu
35.5 amu
With all elements, round A.W.’s to one
decimal place.
Study Check
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What is the Atomic Weight of each
element rounded to 0.1amu?
Na
 Si
 Cl
 K
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Electron Arrangement
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The electrons determine much of the
properties and reactions for that element.
Electrons are arranged first into shells,
and then further into subshells.
Shells are usually indicated by the letter n
and have integer values.
n = 1 is the lowest energy possible.
Shells
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The maximum number of electrons
that each shell can hold depends on
the value of n.
n = 1, can hold
maximum.
 n = 2, can hold
maximum.
 n = 3, can hold
 n = 4, can hold
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two electrons
eight electrons
18 electrons maximum.
32 electrons maximum.
Orbitals
An orbital is a 3D shape that
contains up to two electrons MOST
of the time.
 An s type orbital is spherical in
shape.
 A p type orbital has two lobes along
one of the three axes (x, y, or z).
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Orbitals
Subshells
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Shells are split up into subshells.
Each type of subshell is given a letter
designation – s, p, d, or f. The s and p
orbitals were shown on the previous slide.
Each subshell also has a maximum
number of electrons that it can hold.
s = 2, p = 6, d = 10, and f = 14.
Using Subshell Notation
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The filling order for subshells is:
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1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p,…
For writing electron configurations, write
each subshell followed by a superscript
number indicating the number of
electrons.
Remember that subshells can only hold
as many electrons as stated previously.
What are the Electron
Configurations for:
H
B
O
 Ne
 Mg
 There is a pattern to this!
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Shorthand Method
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For elements with a lot of electrons, the
process is rather tedious.
The shorthand method uses the noble
gases (group 8A) to represent the filled
shell(s) of electrons.
For any element, count back to the last
noble gas encountered. Then, begin with
the next subshell until you are finished.
Study Check
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Write the shorthand electron
configuration for each of the
following:
Mg
 S
 Ti
 Zn
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Energy Level Changes
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Electrons normally reside in the lowest possible
energy levels (called the ground state).
In the presence of heat or light, electrons can
absorb energy and jump to a higher level (shell
#).
In time, electrons will return to the lower energy
state by emitting energy.
Some of these transitions are in turn responsible
for the colors we perceive for different objects.
Periodic Trends
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Many physical and chemical properties
can be predicted using the periodic table.
Valence electrons are the outermost shell
of electrons.
For main group elements, the number of
valence electrons equals the group
number.
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ex) group 2A elements all have two valence
electrons.
ex) group 5A elements all have five valence
electrons.
Periodic Trends
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Electron dot symbols combine the
element symbol with the number of
valence electrons.
Valence electrons are shown as dots,
which are placed one on each side (N-SE-W) until the fifth electron. With the
fifth electron, you will begin pairing them
up.
Table 3.16 shows the Electron dot
symbols of the first four periods of the
main group elements.
Learning Check
A.
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X is the electron-dot symbol for
1) Na
B.
2) K
3) Al

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X
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
1) B
is the electron-dot symbol of
2) N
3) P
Periodic Trends
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Atomic sizes vary following a
pattern.
Sizes increase from top to bottom
 Sizes decrease from left to right
 Figure 3.15 on p. 100 shows relative
sizes
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Periodic Trends
Periodic Trends
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Ionization energy is defined as the
amount of energy required to remove an
electron from an element in its gaseous
state.
• Na(g) + energy  Na+(g) + 1 e
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Ionization energy decreases from top to
bottom
Ionization energy generally increases from left
to right (there are exceptions, but don’t worry
about these).
Periodic Trends
Learning Check

A.
B.
C.
Select the element in each pair with the larger
atomic radius.
Li or K
K or Br
P or Cl
Learning Check
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A.
B.
C.
Select the element in each pair with the higher
ionization energy.
Li or K
K or Br
P or Cl