Chapter 3
Atom Review
(Dalton’s Atomic Theory)
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Atom: the smallest particle that still has
the properties of an element
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Elements are made of atoms and atoms
of the same element are alike
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Atoms combine in order to make
molecules (either elements or
compounds)
Structure of the Atom
Inside the nucleus
A.
 Protons (positive charge)
 Neutrons (no charge)
Outside the Nucleus
B.
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C.
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Electrons (negative charge)
Electrons are orbiting the nucleus so fast
that we can’t determine their exact position
Neutral atoms have no overall charge
They have equal numbers of protons and
electrons
Calculating Protons,
Neutrons, and Electrons

# of protons: Always the same as the
atomic # on the periodic table

#of electrons: usually the same as the
atomic number. (different in atoms that
have a charge)

# of neutrons: Atomic mass – atomic #
Ex. Chlorine has 18 neutrons
Drawing Electrons in their
orbitals (shells)
The first orbital can hold 2 e The second orbital can hold 8 e The third energy level can hold 8 e Valence Electrons: the electrons in an
atom’s outermost shell

Example:
Changing Atoms
Ions- Atoms that carry a charge
A.


Atoms gain/lose electrons from their
valence shell in order to be more stable.
This causes the # of protons to no longer
equal the # of electrons.
Two types of Ions
B.


Anions- Negatively charged atom
(gained e- , Has more e- than p+)
Cations- positively charged atom
(lost e-, has less e- than p+)
Changing atoms (cont.)
 Isotopes- Atoms that have the same
number of protons, but different
numbers of neutrons
A. Changes the atomic mass of the atom
B. The atomic mass written on the periodic
table is the weighted average atomic mass
of ALL the isotopes.

Changing the # of protons = New Element
Developed by a Russian chemist
named Dmitri Mendeleev
(duh-MEE-tree mehn-duh-LAY-uhf)
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Mendeleev used the following categories to
organize his table:
chemical properties
physical properties
atomic mass
density
color
melting point
Valence electrons
Design of the Periodic Table
organizes information in a logical,
usable, and meaningful way
 allows prediction of physical and
chemical properties of an element by
position
 can predict how elements will react
with other elements
 arranged in columns and rows
because of similar characteristics

Columns in the Periodic Table

vertical classification or groupings

often referred to as families or
groups

elements within the same family have
similar properties
Rows in the Periodic Table
horizontal classification or groupings
each row is called a period
elements in a period are not alike in
properties, properties change greatly
across a given row
 the first element in a period is a very
reactive metal
 the last element in most periods is a
noble gas
 only seven periods
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Physical and Chemical Properties
of Metals
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Physical
Properties
luster (shininess)
conductivity of
heat and electricity
high density
high melting point
ductility (they are
ductile)
malleability (they
are malleable)

Chemical
Properties

Tend to lose their
electrons in a
reaction
Metals will have
either 1, 2, 3, or 4
electrons in their
outermost energy
level (depending on the

family)
Alkali Metals
Group 1
 Very reactive because
they only have one
valence electron
 Forms a 1+ ion (ex. Na+)
 Found in nature as a
compound

http://www.youtube.com/wat
ch?v=m55kgyApYrY
 YouTube - Alkali Metals:
Explosive reactions

Alkaline Earth Metals
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Group 2
2 valence electrons
Form 2+ Ions (ex.
Ca2+)
Reactive, but less
reactive than alkali
metals
Transition Metals
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Groups 3-12
Typically have 3
valence electrons
Less reactive than
first 2 families
Most metals we
think of are from this
family
Very good
conductors of heat
and electricity
Nonmetals (right side of PT)
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Physical
Properties
No luster
Don’t conduct heat
or electricity well
Not malleable or
ductile
Can be solids,
liquids, or gases
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Chemical
Properties
Typically gain
electrons to fill
valence shell
Form Negative Ions
(ex. O2-)
React mainly with
metals
Halogens
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Group 17
Have 7 valence
electrons
Very reactive
nonmetals because
they need one
electron for full
valence shell
Are found as solids,
liquids and gases at
room temp
Noble Gases
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Group 18
Have 8 valence
electrons (He only
has 2)
Full valence shell
makes them
unreactive
Also called “inert”
Metalloids (Semi-conductors)

Only 7 elements
(B, Si, Ge, As, Sb, Te, Po)


Classified as
nonmetals but have
some properties of
metals
Can conduct heat
and electricity but
not as well as
metals.