The Lewis Dot Structure for O2

Created by MakeTheBrainHappy.

This is the Lewis Dot Structure for O2, commonly referred to as oxygen gas. Due to oxygen's high electronegativity (affinity for electrons), the pure element is nearly exclusively found in either this state or ozone (O3 - a distinct lewis structure for another post). When drawing the structure, you may replace the individual lines with two dots symbolizing the two electrons contained within the bond. By sharing two electrons each, both atoms fill their valence shells with eight electrons as required under the octet rule for the first three lines of the periodic table. Since this is the double bond, the two atoms create a sigma-pi "sp" hybridized linear bond.

Due to these properties, the molecule is generally considered nonpolar. Between these two atoms, there is no electronegativity difference which means that O2 molecules only interact via weak London Dispersion forces. This leads to the stable confirmation which naturally exists in the atmosphere.

The importance of this element within our chemical systems cannot be understated. Oxygen is the most abundant element on earth, constituting nearly half of the atmosphere and crust [1] and the most abundant element in the universe after hydrogen and helium.

Liquid and Solid Oxygen?

Credit to the Eielson Air Force Base

Although it does not gain as much notoriety as its counterpart liquid nitrogen, a liquified version of oxygen does exist and is most notably utilized for liquid-powered rockets. Liquid oxygen in fact has a lower boiling point (at 90K) than liquid nitrogen (at 77K); however, liquid oxygen reacts violently with organic materials which limits its potential biological applications. Solid oxygen is also theoretically possible to create at a temperature of approximately 55 K.

Importance of Oxygen in Carbon Cycling

Diagram created by eSchoolToday

The carbon cycle is traditionally thought of as an producer-consumer relationship with the autotroph (i.e. photosynthesizing orgasm) requiring an input of CO2 (generally) and outputting O2 in the process. The consumer then utilizes some of the released O2 for respiration. While this generally encapsulates the relationship, more complex theories will touch upon the role of decomposers within both photosynthetic and oceanic "sinks" of carbon.

Diagram from the NASA Earth Observatory

The "Oxygen" Revolution

Figure from a professor at the University of Waterloo 

Oxygen has not always been a significant component of earth's atmosphere. In fact, its rapid appearance can be attributed to the emergence of respirating autotrophs releasing oxygen into the atmosphere. However, these same forms of life that were releasing this gas needed to evolve mechanisms to avoid its dangerous effects toward the forms of life which existed at that time due to the drastic change in the atmosphere. Some scientists have termed this occurrence as the "Great Oxygen Event" with numerous hypothesis as its effect on biological life nearly two billion years ago.

[1] https://openstax.org/books/chemistry-2e/pages/1-2-phases-and-classification-of-matter