DE Chemistry – King William High School
 Elements are pure substances
 Symbols – you know these from
last year 
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Dmitri Mendeleev (1872)
Periods – horizontal rows
Group (family) – vertical column (tend to
have the same reactivity)
Representative (or main-block) elements =
groups 1-2, 13-18)
Transition elements (“junk in the middle”)
Lanthanides & actinides (inner transition
metals)
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Alkali metals (group 1) – the most reactive
metals
Alkaline earth (group 2) – not as reactive as
alkali
Halogens (group 17) – most reactive
nonmetals
Noble gases (group 18) – inert…don’t react!
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Separates the metals from the nonmetals
Metals to the left (ductile, malleable, good
conductors of heat)
Nonmetals to the right (poor conductors, low
MP, low density)
Metalloids on the staircase (EXCEPT Al
Aluminum is a metal!)
Metalloids are semiconductors because they
can act as conductors and insulators
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An atom is the smallest part of an element
that retains the characteristics of that
element
1808 – John Dalton’s Atomic Theory (see
page 105 to refresh your memory)
J. J. Thompson (1897) – plum pudding model
Rutherford – Gold foil experiment (discovered
the nucleus)
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Subatomic particles – proton, electron &
neutron
Protons & neutrons contain most of the mass
in the nucleus
Electrons are very small and zoom around
outside of the nucleus
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Atomic number = number of protons
Atomic number = number of electrons (in a
neutral atom)
Mass number = protons + neutrons
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Isotopes – same element with different
number of neutrons
Carbon-12 & carbon-13
Average atomic mass = decimal # on periodic
table
Formula for calculating…
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A new element Fulksium has been discovered
at KWHS. It has two isotopes: Fu-363 has a
relative abundance of 37% and Fu-364 has a
relative abundance of 63%. What is its
average atomic mass?
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Energy level = the specific energy of an
electron
The higher the number then the higher the
energy
The higher the energy then the further away
form the nucleus
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Valance electrons
Atomic size or radius (Fr)
Ionization energy (energy needed to remove
an electron)  F
Metallic character (loses valence electrons
easily)  Fr
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Only for elements…no compounds.
As
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Cl
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Ne
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