The Periodic Table - Crestwood Local Schools

The Periodic Table
Part One
The Basics
 What does periodic mean?
 Having or marked by repeated cycles
 What things in our everyday life do we notice
as cyclic or periodic?
 What are some of the patterns you notice
on the periodic table?
 There are many important people who
played a key role in organizing the
elements in such an intricate fashion…
Antoine Lavoisier (1790’s)
 Compiled a list of
known elements at
the time (23)
 What elements do you
think were included
here?
 Gold, silver, oxygen,
carbon
 The 1800’s brought
about big changes…
 What are some big things that may have
affected the knowledge of chemistry?
 Electricity
 Development of the spectrometer
 Industrial revolution (mid-1800’s)
 Lead to many chemical industries…soaps, dyes,
fertilizers
 But not all good things came from the revolution
 Chemical pollution now an issue
 70 known elements by the 1870
In addition to new elements…
 New scientific data that provided insight into the
properties of compounds and elements
 A tool for organization became necessary
 Big step: 1860
 Scientists agreed on a method for accurately
determining the atomic masses of the elements
(finally!)
 What would be the problem with not having a
universal way to measure the mass of elements?
 Now the search for relationships between mass
and elements was on…
John Newlands (1864)
 English chemist
 Proposed organization scheme
 Noticed elements were arranged by
increasing atomic mass
 Also, their properties repeated every
eigth element
 1st and 8th
 2nd and 9th
 What do were call this repeating
pattern?
 Newlands called it: The Law of
Octaves
 Octave is a group of musical notes
that repeats every eighth tone
 Newlands organized
the first 14 known
elements
 Elements with similar
properties were in the
same row
 How does this
compare with our
current periodic table
 Newlands organized the first 14 known elements
 Elements with similar properties were in the same row
 How does this compare with our current periodic table
 The Law of octaves was not readily
accepted b/c it did not work with all
elements
 Newlands law was also criticized b/c the
use of the word octave was considered
very “unscientific”
 The important thing was that Newland
recognized that properties of elements
were repeated
Lothar Meyer (1869)
 German chemist
 Demonstrated
connection between
atomic mass and
elemental properties
 Did not receive as
much credit as Dmitri
Mendeleev because
he did not publish his
organization scheme
first
Dmitri Mendeleev (1869)
 Russian chemist
demonstrated connection
between atomic mass and
elemental properties
 Noticed (like Newlands) that
when elements were put in
order of atomic mass there
was a periodic repetition of
their elemental properties
 Arranged elements in order
of increasing atomic mass
into columns with similar
properties
 This was the first periodic
table
 Mendeleev’s table was widely accepted
because it predicted the existence and
properties of undiscovered elements
 Blank spaces on the table
 Predicted properties of yet to be
discovered elements such as scandium,
gallium, and germanium
But there were problems…
 New elements discovered and atomic
masses were more accurately determined
 Elements in Mendeleev’s table not in
correct order
 Arranging elements by mass now put
groups of elements together with different
properties
Henry Moseley (1913)
 English Chemist
 Figured out the problem
with Medeleev’s Table
 What did Moseley
Discover before?
 Atoms of each element
contain unique number of
protons in their nuclei
 He arranged elements in
order of increasing atomic
number and not
increasing atomic mass
Problem Solved!
 Moseley’s arrangement solved the
problems with Mendeleev’s table
 His arrangement resulted in clear periodic
patterns of properties
 Lead to Periodic Law:
 Statement that there is a periodic repetition of
chemical and physical properties of the
elements when they are arranged in
increasing atomic number
Modern Periodic Table
What’s in the box?
 What does the 1 stand
for?
 Atomic Number
 This tells us what about an
atom of H?
 # of protons
 What does the 1.007947
stand for?
 Atomic Mass
 This tells us what about an
atom of H?
 Mass in nucleus (# of
protons and neutrons)
 On the modern periodic table, how are
elements arranged?
 In order of increasing atomic number, left to
right
 What do we call the columns (up and
down) on the periodic table?
 GROUPS (or families)
 What do we call the rows (left and right) on
the periodic table?
 PERIODS
Periods
 What does periodic mean?
 Having or being marked by repeated cycles
 What element does period 1 begin with?
H
 How many periods are there on the table?
7
Groups
 Two different number systems for
groups. In the first numbering system,
groups are number 1-8 and each number
is followed by either an A or B
 The groups labeled A are the main groups (1A
thru 8A)
 Representative elements
 This is because they possess a wide range of chemical and
physical properties
 The groups designated with a B (1B thru 8B) are
found in the center
 Transition Elements
 A more recent numbering system has been
devised numbering 1-18