Look up the following information for the element iridium: (i) number of protons, neutrons, and electrons; (ii) atomic number and average atomic mass; (iii) the charge of the anion(s) or cation(s) that it commonly forms;
Look up the following information for the element iridium: (i) number of protons, neutrons, and electrons; (ii) atomic number and average atomic mass; (iii) the charge of the anion(s) or cation(s) that it commonly forms; (iv) the mass of its two most common isotopes and the number of protons and neutrons in each one. Also, comment briefly on the presence of this element in meteorite craters and the significance of this observation.
The Correct Answer and Explanation is :
Iridium (Ir) is a dense, corrosion-resistant metal with the atomic number 77. Here’s a detailed breakdown of its properties:
(i) Number of Protons, Neutrons, and Electrons:
- Protons: All iridium atoms have 77 protons, defining the element’s atomic number.
- Electrons: In a neutral iridium atom, there are 77 electrons, balancing the positive charge of the protons.
- Neutrons: Iridium has two stable isotopes:
- Iridium-191 (^191Ir): 77 protons + 114 neutrons = 191 nucleons.
- Iridium-193 (^193Ir): 77 protons + 116 neutrons = 193 nucleons.
(ii) Atomic Number and Average Atomic Mass:
- Atomic Number: 77
- Average Atomic Mass: Approximately 192.22 u, calculated as the weighted average of its isotopes’ masses and their natural abundances.
(iii) Common Oxidation States:
Iridium exhibits multiple oxidation states, including +1, +2, +3, +4, and +6. The +3 oxidation state is particularly stable and prevalent in its compounds.
(iv) Masses and Neutron Counts of Common Isotopes:
- Iridium-191 (^191Ir): Mass number 191, 77 protons, 114 neutrons.
- Iridium-193 (^193Ir): Mass number 193, 77 protons, 116 neutrons.
Iridium in Meteorite Craters:
Iridium is rare in Earth’s crust but more abundant in meteorites. Elevated iridium levels in geological layers, such as the Cretaceous–Paleogene boundary, have been linked to asteroid impacts. This correlation supports the hypothesis that a massive asteroid impact contributed to the mass extinction event 66 million years ago, including the demise of non-avian dinosaurs.
In summary, iridium’s unique properties and its association with extraterrestrial impacts provide valuable insights into both its chemical behavior and Earth’s geological history.