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CH 18 Properties of Atoms and the
Periodic Table
Structure of • Chemical symbol —
shorthand way to write
the Atom
element’s name; 1 or 2
• 1st letter ALWAYS
capitalized and if there is
a 2nd it is lowercase
• Case sensitive: CO≠Co
• Some use Latin names,
Ag is silver—Argentum in
• System used worldwide
• Atoms—basic building
blocks of all matter
• Composed of:
• Protons—in nucleus; +
• Neutrons—nucleus;
• Electrons—around
nucleus; • Nucleus—positively
charged center of
• Quarks—what
protons and
neutrons are madek
of;6 types
• Up, down, charm,
strange, top &
• 3 arranged one
way=proton (p+)
• 3 arranged
way=neutron (n°)
Electron models
• Atomic models have
changed thru-out
Models showing
where e- is located
also changed (pg
• Bohr’s model is
the one we recognize
Electron models
• Electron cloud is
current model
• Cloud is the
probable region
where you would
find an e• Cloud 100,000
times larger than
nucleus! But e- is
MUCH smaller than
a p+
Masses of Atoms
Sec 2
• Neutral atom— equal #
of p+ and e• Atomic mass unit
(amu) used to measure
atomic particles
• Equal to 1/12th the
mass of a carbon atom
Masses of Atoms Sec 2 cont.
• Atomic # = # of p+
• Atomic mass=# of p+
and n°
(# above chem.
symbol on your chart—larger #)
• Atomic mass – atomic # = # of n°
• Isotopes—atoms of
the same element
that have a different
# of n°
Sec 3 Periodic Table
• Dmitri Mendleleev—Russian
chemist (late 1800’s)
arranged elements in order
of increasing atomic mass
Left blank spaces due to
undiscovered elements
Vertical columns (18) called
• # of outer e- are the same
in each group
Chemical properties are the
same for the elements in
each group
Horizontal rows called
• Metals—all elements left of the stair step
• Properties: solids at room temp (except ?),
shiny, good conductors of heat and electricity
Metalloids—elements near the stair step
Have properties of both metals and non-metals
Non-metals—right of stair step
Properties: most are gases, some brittle solids, poor
conductors of heat/electricity
Groups 312 called Transition elements: metals, but
have properties not found in elements of other groups
• Energy levels of e• 1st level, closest to
the nucleus,
lowest E, only
holds 2 e• 2nd level holds 8 e• 3rd level holds 18
e• 4th level holds 32
• e- dot diagrams—represents the outermost e- of
an element
Called Lewis structures
Chemical symbol and the # of e- in the outer
level placed around the chem symbol using dots