What is the periodic table?
• A compact way of organizing the elements
that contains a lot of information and
allows us to make predictions about the
behavior and properties of the elements.
• Elements
History of the Periodic Table
• End of the 1700’s – less than 30 elements
known.
• Many elements were discovered during
the 1800’s. Many experiments were done
to determine atomic masses.
John Newlands - Octaves
• 1864: Newlands noticed that when the
known elements were arranged by atomic
masses, their properties repeated every
8th element.
• Law of Octaves did not work for all known
elements.
• Key idea was correct: Properties of
elements do repeat in a periodic way.
Mendeleev & Meyer
• 1869: Mendeleev produced 1st accepted
periodic table.
• Elements ordered by increasing atomic
mass into columns with similar properties.
• Predicted the existence & properties of
undiscovered elements.
• Not totally correct. As more accurate
determinations of atomic mass were made,
several elements weren’t in the right place.
Remember
• 1860’s: No subatomic particles had been
discovered yet.
• People were going by Dalton’s billiard ball
model of the atom.
1913 – Henry Moseley
• By 1913, protons & electrons discovered.
Neutrons predicted.
• When cathode rays hit stuff, they produce X-rays.
• Mosely used 30 different elements as “stoppers”
• Found that the greater the atomic weight of
the “stopper,” the shorter the wavelength of
the x-rays.
•
What does any good scientist do?
PLOTS THE DATA!
•Tried correlating the wavelength of the x-ray
with the atomic mass of the stopper. Not so
nice. Change in  much more regular than
change in atomic weight.
•Then tried correlating the wavelenth of the
x-ray with an integer, n. Got a very pretty
graph.
Atomic Number - 1913
• Mosley interpreted the integer, n, to be the
positive charge on the nucleus.
• Mosley suggested that the size of the
nuclear charge increased by 1 with each
step up the periodic table. (Before, it was
organized by atomic weight.)
• Moseley determined that atoms of each
element contain a unique number of
protons – atomic number.
• Moseley rearranged Mendeleev’s periodic
table by atomic number instead of mass.
• Problems disappeared.
Periodic Law
• There is a periodic repetition of chemical
and physical properties of the elements
when they are arranged by increasing
atomic number.
Vocabulary of the P.T.
• Columns are called groups or families. 2
different notations.
– 1 thru 18, Arabic numerals.
– Split into A & B groups. Use Roman numerals.
• A-Group = Columns 1,2,13-18 = representative
elements
• B-Group = Transition metals
• Rows are called series or periods.
Numbered 1 thru 7.
Classifying the Elements
• 2/3 of the elements are metals.
• Remaining elements are non-metals and
metalloids (semi-metals).
• Metalloids have some properties of metals
and some properties of nonmetals.
• Know the “staircase” dividing line on the
P.T. between metals & nonmetals.
Everything to left, except H, is a metal.
Metalloids
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Boron, B
Silicon, Si
Arsenic, As
Tellurium, Te
Astatine, At
Germanium, Ge
Antimony, Sb
Names of Families
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Group 1 = Alkali Metals (IA)
Group 2 = Alkaline Earth Metals (IIA)
Group 17 = Halogens (XVIIA)
Group 18 = Noble Gases (XVIIIA or O)
– The noble gases are extremely unreactive.
Weren’t discovered until 1890’s.
Transition Metals
• Elements in Columns 3 through 12
• Also called the group B elements
– Transition elements form brightly colored salts
and brightly colored solutions.
– Have multiple, positive oxidation states
• Actinide and Lanthanide series = inner
transition elements
Calcium Metal