Properties & Reactions of Arsenic

Arsenic in the Periodic Table
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Periodic Table

Some properties of arsenic are summarized in the table below.

Atomic Number:
  33  
Atomic Radius:
  0.125 nm
Atomic Symbol:
  As  
Melting Point:
  ~817 ºC
Atomic Weight:
  74.9216  
Boiling Point:
  603 ºC (sublimation)
Electronic
Configuration:
  [Ar] 4s23d104p3  
Oxidation States:
  5,3,2,-1

Arsenic falls below phosphorus in the Table of Elements, and the two elements share many similar properties (see table below). However, in spite of the similarities, there exist some critical differences. Arsenic is toxic to both animals and plants, while phosphorus is a beneficial nutrient for all animals and plants.

Comparison of Arsenic and Phosphorus

Property
Arsenic
Phosphorus
Atomic Radius, nm
0.125 (as +3)
 0.093 (as +5)
Predominant Oxidation States
+5,+3
+5
H3AsO4 or H3PO4 – pK1
2.20
2.15
H3AsO4 or H3PO4 – pK2
6.97
7.20
H3AsO4 or H3PO4 – pK3
11.53
12.38
Symmetry of AsO4 or PO4
tetrahedral
tetrahedral

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