Atomic Structure Review
• Atoms are made of protons, electrons,
and neutrons.
• Elements are atoms of only one type.
• Elements are identified by the atomic
number (# of protons in nucleus).
Energy Levels Review
• Electrons are arranged in a region around
the nucleus called an electron cloud.
Energy levels are located within the cloud.
• At least 1 energy level and as many as 7
energy levels exist in atoms.
Energy Levels Review
• Electrons in levels farther away from
the nucleus have more energy.
• Inner levels will fill first before outer
levels.
Energy Levels & Valence Electrons
• Energy levels hold a specific amount of
electrons:
–1st level = up to 2
–2nd level = up to 8
–3rd level = up to 8
(first 18 elements only)
Energy Levels & Valence Electrons
• The electrons in the outermost level
are called valence electrons.
–Determine reactivity - how
elements will react with others to
form compounds
–Outermost level does not usually fill
completely with electrons
Dmitri Mendeleev—published the
1st version of the periodic table (1869)
_________
•Arranged in order of increasing atomic
mass
•Left gaps for missing
(or undiscovered) elements
•Because of the consistency of
elements, Mendeleev predicted the
properties of many of the missing
elements quite accurately.
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Henry Moseley—rearranged
Mendeleev’s table into the current version
Arranged by atomic number
(number of protons)
With Moseley’s table, it
became clear how many
elements were still undiscovered
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The Modern Periodic Table
In the modern periodic table, there are 7 rows called
periods. A period is a row of elements in the periodic
table whose properties change gradually and
predictably.
The periodic table also has 18 columns
called groups. A group contains
elements that have similar physical or
chemical properties. A group is also
known as a family.
The Modern Periodic Table (cont’)
The periodic table is divided into two main
parts: The Representative Elements and The
Transition Elements
Each element can
be classified as a
metal, nonmetal,
or metalloid.
metal- element that:
1) has luster (reflects light)
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2) malleable (can be
flattened into sheets)
3) ductile (can be stretched
into a wire)
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4) good conductors of heat and electricity
nonmetal—element that is:
1) usually a gas or a brittle solid
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2) poor conductor of heat and electricity
metalloid—element that share
some properties of both metals and nonmetals.
These are sometimes called semimetals.
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Element
symbol
1
H
1.008
Atomic
number
Atomic
mass
Symbol—represents the name of
the element. Always written
with 1st letter capitalized and
2nd letter (if applicable) lower
case.
Atomic number—represents
the number of protons in the
nucleus
Atomic mass—number of
protons plus neutrons. On the
periodic table, that is the
“relative” mass and is calculated
based on the percentage of the
different isotopes.
Representative Elements—elements in
groups 1 & 2, and 13-18 or the “A” elements
in the periodic table; includes metals,
metalloids, and nonmetals
Group 1 or 1A
Called Alkali Metals
Highly reactive in water and
combining with other
substances
Reactivity gets
greater as you
go down the
table
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Lithium: found in batteries (esp for camera)
Sodium: found in table salt in combination with chloride
Potassium: found in bananas, sunflower seeds, and
potatoes
Group 2 or 2A
Called Alkaline Earth Metals
 Slightly less reactive than the
alkali metal in the same period.
Magnesium: combined
to make Epsom salt
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Calcium: milk and other dairy products;
in your bones
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Group 17 or 7A
 Called Halogen Group
Means “salt formers”
 Alkali + Halogen = Salt
Fluorine— prevent tooth decay
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Chlorine— in table salt; kills bacteria in water
Bromine— dyes, pesticides, medicines
Iodine— disinfectant for wounds; photography;
put in table salt for health
Group 18 or 8A
Called Noble Gases
 Rarely combines with other elements
because it has a full outermost shell
ONLY found in nature uncombined
Helium— balloons, blimps
Neon— signs
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Ne— red-orange
He— yellow
Ar— bluish-violet
Argon—most abundant Noble gas; protective
gas shield for welding, light bulbs, etc.
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Krypton—used in bulbs to help them burn longer
Transition Elements
1) elements in Groups 3-12 or the “B” elements on the
periodic table
2) all are metals.
3) Most found combined to form ores
Transition Metals
Most have a higher melting point than
representative elements
W-Tungsten used in light bulbs;
highest boiling point at 3,410 C
Hg-Mercury used in thermometers and
barometers
Inner Transition Elements
Lanthanides
oAlso called rare earths, because at one time they
were thought to be scarce
oSoft enough that they can be cut with a knife
oAre so similar, they are hard to separate when
found together in ores
Inner Transition Elements
Actinides
o Are all radioactive
oMost are synthetic
oCalifornium—252 is used to
kill cancer cells
Synthetic elements can be made using a
particle accelerator. Atomic nuclei are
caused to collide at high speeds hoping
they will fuse together forming new
elements. They are called “heavy”
elements and usually last only a few
seconds before decaying into a lighter
element.
Transition Elements and Dentistry
Dentists used to use amalgam to fill cavities
which was made of a mixture of silver,
copper, tin, and mercury. Due to concerns
with mercury, new resins, composites, and
porcelains that are the same color as the
tooth have been developed.
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www.gs-titanium.com
Orthodontists are now using nickel and
titanium alloys for wire braces. These wires
have shape memory. When they are
heated, they can “remember” their shape
and will return to that shape if forced out of
it.