History of the Periodic Table

1
History of the Periodic Table

• Aristotle first classified the known elements
  into three groups
• Few elements, classified by physical
  characteristics
• Earths
• Gases
• Solids

2
Early 19th century attempts at classification

• Dobereiner
• triads
• Newlands
• Law of octaves

3
Eight columns of repetitive properties

• Meyer
• arranged by atomic mass eight columns with
  elements of similar properties in the same column
• Mendeleev
• Eight columns similar to Meyers table, but saw
  inconsistencies and left spaces

4
Current arrangement

• Moseley
• Determined the atomic number of the elements and
  arranged in order of atomic number rather than
  atomic mass

5
Navigating the table

• Periods/Series
• These are the rows. When the elements are
  arranged in atomic number order, the properties
  of the elements repeat periodically the
  periodic law
• Elements in the same period have the same number
  of energy levels, hence the same n quantum
  number

6
Navigating the table cont.

• Groups or Families
• These are the columns
• The elements in a group or family have similar
  physical and chemical properties

7
Representative Elements

• Groups 1A through 7A and group 0 are the
  representative elements
• 1A are the alkali metals
• 2A are the alkaline earth metals
• Group 6A are the chalcogens
• Group 7A are the halogens
• Group 0 are the noble gases

8
Metals

• The great majority of the elements are classified
  as metals.
• Metals have 3 or less electrons in the outer
  level, thus tend to form cations
• The metals with d sublevels filling are the
  transition metals
• The metals with f sublevels are the rare-earth
  elements
• 4f lanthanide series
• 5f actinide series

9
Nonmetals

• Nonmetals have 5 or more electrons in the outer
  level and tend to form anions

10
Metalloids

• Are located on the periodic table along the heavy
  stairstep line
• Metalloids exhibit some properties
  characteristic of metals and other properties
  characteristic of nonmetals

11
Periodic Trends

• Atomic Radius the average size of the electron
  cloud
• Increases as you move down a group
• Decreases as you move from left to right across a
  period

12
Ionization energy

• The energy required to remove an electron from an
  atom
• Generally decreases as you move down a group
• For the representative elements generally
  increases as you move from left to right across a
  period
• This is due to the greater attraction of the
  nucleus for the electrons

13
Electronegativity

• The tendency for the atoms of the element to
  attract electrons when they are chemically
  combined with atoms of another element
• Decreases as you move down a group
• Generally increases as you move from left to
  right across a period (excluding the noble gases)
• Trends in the transition metals are less regular

14
Ionic Size

• Positive ions are always smaller than the neutral
  atoms from which they form
• Negative ions are always larger than the neutral
  atoms from which they form