Download 02 The structure of the periodic table II

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Groups
The Structure of the Periodic
Table II
 Another
way of grouping the
elements is by their properties
 Groups 1 ~ 12: metals
1 - 2: metals
 Groups 3 - 12: transition metals
 Groups
Groups
 Groups
13 ~ 18: nonmetals
17: halogens
 Group 18: noble gases/inert
gases
 Group
Organizing Elements by Properties
7
of the 9 elements that lie
along the diagonal ‘staircase’
 Metalloids
 Semimetals
 Semiconductors
13Al, 84Po
are the exceptions
they’re considered metals
Development of the Periodic Table
 Only
13 elements were identified
by the year 1700
 As scientists discovered new
elements, a way was needed to
classify and organize them
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Development of the Periodic Table
 As
the number of known elements
increased, scientists began to think
about organizing them in some way
 Between 1829 to 1869, many
different classification systems were
proposed, each organizing the
elements in a different way
Development of the Periodic Table
 In
1869, 2 scientists independently
published nearly identical
classification schemes:
 Dmitri Mendeleev (Russia)
 Lothar Meyer (Germany)
Development of the Periodic Table
Development of the Periodic Table
 Both
 The
noticed that properties
recurred periodically when the
elements were arranged in order
of increasing atomic mass
 How is the table currently
organized?
concept of the atomic number
didn’t exist yet
 The tables developed by
Mendeleev and Meyer were the
forerunners to the modern
periodic table of the elements
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Development of the Periodic Table
Development of the Periodic Table
 Mendeleev
is given credit for the
modern periodic table for 2
reasons:
 1) He insisted that chemically
similar elements be listed in the
same columns (groups) on the
table
 2)
Development of the Periodic Table
Development of the Periodic Table
 In
1913 an English physicist
named Henry Moseley
discovered the atomic number
 This occurred 2 years after
Rutherford proposed the
nuclear model of the atom
He left blank spaces on his
table where elements didn’t seem
to ‘fit’ in terms of their properties
 He hypothesized that these
elements simply hadn’t been
discovered yet
 He was right!
 Moseley
bombarded different
elements with electrons and
determined the frequencies of
X-rays that were emitted
 He found that each element produces
X-rays of a unique frequency
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Development of the Periodic Table
 He
arranged the frequencies from
lowest to highest, and assigned each
element a number -- based on it’s
position -- starting at #1
 The ‘atomic number’ that he assigned
turned out to be exactly equal to the
number of protons in the nucleus of
each type of atom!
Development of the Periodic Table
discovery of the atomic number
clarified some inconsistencies in
Mendeleev’s periodic table
 It made sense for iodine (I) to come
after tellurium (Te)
 The
 53I
 52Te
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