Periodic Table of the Elements Aim PT1

1
Periodic Table of the ElementsAim PT1 How did
the Periodic Table develop?
2
Why is the Periodic Table important to me?

• The periodic table is the most
  useful tool to a chemist.
• It organizes information about
  all the known elements
• It shows trends and patterns of elements in the
  table as well
• You get to use it on every test.

3
Pre-Periodic Table Chemistry

• Imagine going to a grocery store
  with no organization!!
• There was initially no organization of the
  elements either
• It was difficult to relate elements to each other
• Chemistry and the elements didnt make sense

4

• Elements in the Periodic Table
  needed to be classified
• Classification
• grouping elements based on
  similarities and differences
• Cross classification
• the classifying of elements into more than one
  category at a time
• Examples
• Deck of cards Suits and Numbers
• Periodic Table Groups and Periods

5

• Mendeleev's Periodic Table
• Dmitri Mendeleev (1869) prepared a card
  for each of the known elements
  which listed each elements
• symbol
• atomic mass
• chemical properties
• Reactivity of each
• High reactivity vs low reactivity vs no
  reactivity
• He arranged the cards in order of increasing
  atomic mass
• A pattern, emerged which developed into the
  Periodic Law

6

• MENDELEEV'S PERIODIC LAW
• When the elements are arranged in
  increasing order of atomic mass, the
  chemical properties repeat themselves
  periodically
• Each row or PERIOD was arranged in order of
  increasing atomic mass
• At the end of a row or PERIOD, the properties of
  the elements repeated themselves
• Example whenever a total of eight electrons
  showed up in the valence shell, a Noble Gas (an
  unreactive element) was reached

7

• MENDELEEV'S PERIODIC LAW
• In each row or PERIOD
• Each element in a period had the same number of
  energy levels
• And the characteristics would repeat themselves
  in the next row or PERIOD
• Therefore, each vertical column was called a
  GROUP or FAMILY
• As you go down a group
• you find the same physical and chemical
  characteristics in each element of the GROUP
• Example He, Ne, Ar, Xe, all are Noble gases and
  are unreactive elements due to the Duet and
  Octet Rules

8

• Example is sodium more similar to
  potassium or magnesium?
• Sodium and magnesium are in the same
  period of the table
• So they are both filling the same valence shell
• Sodiums electron configuration 2 8 1
• magnesiums configuration 2 8 2
• Both are filling the 3rd shell of their atoms
• But sodium is much more reactive in water than
  magnesium

9

• But sodium and potassium are in the same
  group
• Both have 1 electron in the valence shell
• Both react violently in water
• Both are soft metals
• The number of electrons in the valence shell
  determine the chemical properties and reactivity
  of each element
• Elements with the same number of valence
  electrons have similar properties

10
Moseley's Periodic Table
(or the Modern Periodic Table)

• Henry Moseley noticed that when all the elements
  were arranged in order of mass a few were not in
  the right family with respect to properties
• Moseley used a procedure called X-ray diffraction
  to determine the atomic number of the elements
• When the elements were arranged in
  increasing order of atomic number, the
  discrepancies in Mendeleev's table disappeared

11
Moseley's Periodic Table (or the Modern
Periodic Table)

• THE PERIODIC LAW
• When the elements are arranged in
  increasing order of atomic number, the
  chemical properties repeat themselves
  periodically
• The modern Periodic Table is arranged in order of
  increasing atomic number
• Side note Moseley died at the Battle of
  Gallipoli in WWI after volunteering for the Army.
  He would have won the Noble Prize in 1916 if he
  had not been killed. The British government
  never allowed prominent scientists or scholars to
  volunteer again for active service