Periodic table

• Döbereiner’s Triads:

  • In 1829, he classified some elements into groups of three, called triads
  • Elements in a triad had similar chemical properties and orderly physical properties
  • The middle element had an atomic weight almost arithmetical mean of the other two elements
  • Döbereiner’s could only identify three triads and failed to arrange all known elements in triads
• Newlands Law of Octaves:

  • Elements arranged in increasing order of atomic weight, every eighth element had similar properties
  • The law was only applicable till calcium and not to elements of higher atomic masses
  • Position of hydrogen along with fluorine and chlorine was not justified based on chemical properties
  • New elements discovered later could not fit in this periodic table
• Dmitri Ivanovich Mendeleev:

  • Father of Periodic Table
  • In 1869, published a table of elements arranged by increasing atomic weight
  • Periodic Law: properties of elements are periodic function of their atomic weights
  • Left vacant spaces for undiscovered elements
  • Lother Meyer proposed that physical properties of elements are periodic function of their atomic weight
• Modern Periodic Table:

  • The horizontal rows are called PERIODS, with seven periods
  • The vertical columns are called GROUPS or FAMILIES, with eighteen groups
  • Elements in the same group have similar physical and chemical properties
  • Periodicity is the repetition of elements with similar properties at regular intervals based on atomic numbers
  • Periodicity is due to similar outer electronic configuration
• Merits of Mendeleev’s Periodic Table:

  • Systematic study condensed the study of elements to only 8 groups
  • Prediction of new elements and their properties
  • Correction of certain atomic masses
• Defects in Mendeleev’s Periodic Table:

  • Position of hydrogen was unclear
  • Separation of chemically similar elements
  • Grouping of chemically dissimilar elements
  • Inversion in the periodic table
  • No separate places for isotopes
  • Lanthanides and actinides were not given places
• Naming of elements with atomic numbers greater than 100:

  • Names derived using roots for three digits in the atomic number and adding the ending -ium
  • Example: Unnilunium (Unu) for atomic number 101, Mendelevium (Md)
• Electronic Configuration and Periodic Table:

  • Period 1: 1s orbital, 2 elements, very short period
  • Period 2: 2s 2p orbitals
• Periodic Table Information:
• Period 1:

  • Orbitals filled: 1s
  • Number of elements: 2
  • Name of the period: Very short period
• Period 2:

  • Orbitals filled: 2s 2p
  • Number of elements: 8 (2 + 6)
  • Name of the period: Short Period
• Period 3:

  • Orbitals filled: 3s 3p
  • Number of elements: 8 (2 + 6)
  • Name of the period: Short Period
• Period 4:

  • Orbitals filled: 4s, 3d, 4p
  • Number of elements: 18 (2 + 10 + 6)
  • Name of the period: Long Period
• Period 5:

  • Orbitals filled: 5s, 4d, 5p
  • Number of elements: 18 (2 + 10 + 6)
  • Name of the period: Long Period
• Period 6:

  • Orbitals filled: 6s, 4f, 5d, 6p
  • Number of elements: 32 (2 + 14 + 10 + 6)
  • Name of the period: Very Long period
• Period 7:

  • Orbitals filled: 7s, 5f, 6d, 7p
  • Number of elements: 27 (2 + 14 + 10 + 6)
  • Name of the period: Very Long period
• Classification of elements into s, p, d, and f blocks:

  • S-Block elements (Representative elements) have the last electron entering the s orbital of the valence shell
  • General electronic configuration: [Noble Gas] ns 1 - 2
  • S-Block elements consist of two groups:
  • Group 1: Alkali metals
  • Group 2: Alkaline earth metals
• 1. Block elements (Representative elements) have the last electron entering the p orbital of the valence shell

  • General electronic configuration: [Noble Gas] ns 2 np 1 - 6
  • P-Block elements consist of six groups: Group 13 to Group 18 elements
• 1. Block elements (Transition elements) have the last electron entering the d orbital of the penultimate shell

  • General electronic configuration: [Noble Gas] (n - 1)d 1 - 10 ns 1 - 2
• 1. Block elements (Inner Transition elements) have the last electron entering the f orbital of the antepenultimate shell

  • General electronic configuration: [Noble Gas] (n - 2) f 1 - 14 (n - 1) d 0 - 1 ns 1 - 2