Properties of Oxygen
Article objectives
- This article aims to show a variety of properties related to the element oxygen.
Introduction
Oxygen is one of the most common and useful elements in the world, particularly because a good portion of what humans breathe is oxygen. It is the 8th periodic element with a molar mass of \(16.00\) grams, and it typically has six valence electrons. Since oxygen has an atomic number of \(8\), a neutrally charged oxygen atom has \(8\) protons and \(8\) electrons. In this article we will discuss properties of oxygen and where it is found.
Bonding Pairs
As stated before, oxygen has six valence electrons. A full octet, a stable configuration, has eight valence electrons, so to get those extra valence electrons, oxygen atoms typically form two bonds when bonding covalently. This is also the reason why oxygen tens to form \(-2\) ions. Oxygen will only form a different number of bonds in radicals (molecules that are unstable because they don't have the proper number of electrons) and in polyatomic ions.
Example 1: Nitrogen monoxide is one radical with oxygen. It has a chemical formula \(NO\). The total number of valence electrons in this molecule is \(11\), so both chemicals cannot have a stable electron configuration simultaneously. The molecule can have either two covalent bonds or three-both structures are equally unstable.
Common Compounds with Oxygen
Many common compounds with oxygen atoms are molecules that have common interactions with humans in everyday life.
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Water: \(H_2O\). We all know what this does, it hydrates our body. It consists of an oxygen atom having two single bonds to hydrogen atoms, as well as two lone pairs of electrons. The molecule as a whole is neutral in charge.
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Hydroxide: \(OH^{-}\). This is what you get if you remove a hydrogen ion from a water molecule. Because this is doable, water is an acid--a chemical that will give up one or more hydrogen ions to another chemical. The hydroxide ion, with its negative charge, is typically found in solution with positively charged ions. These ions include the cations of metals, as well as positively charged hydrogen ions. Also, the hydroxide ion is often formed as a result of this reaction:
$$H_2O \rightarrow H^{+} + OH^{-}$$
3. Elemental oxygen: \(O_2\). This is the chemical formula for pure oxygen. Since oxygen atoms naturally come in pairs, oxygen is called a diatomic element. This has to do with the fact that two oxygen atoms with a double bond between them are more stable than a lone oxygen atom. The double bond gives each oxygen atom in the molecule a full octet of valence electrons.
4. Ozone: \(O_3\). Large clouds of this fill certain layers of our atmosphere, serving as a shield from UV rays from the sun. This is one of the only exceptions to how oxygen bonds. The central oxygen has a double bond to one of the other oxygen atoms and a single bond to the third. Lone pairs are allotted to the oxygen atoms so that all three have full octets.
5. Hydronium \(H_3O^{+}\). This ion reacts with hydroxide to form water (usually interahcnged with just a hydrogen cation)
Here are Lewis Structures for the above compounds:
Water
Hydroxide ion
Elemental oxygen
Ozone
Hydronium ion
Note that each neutrally charged oxygen atom has two lone pairs and two bonding pairs. If the individual oxygen atom has a nonzero charge, these numbers vary. As electrons in bonding pairs are shared with other atoms, they spend less time contributing their charge to the oxygen atom, making its formal charge positive, as in hydronium ions. On the other hand, in the hydroxide ion, it has more lone pairs than bonding pairs. The lone pairs spend all of their time contributing their negative charge to the oxygen atom as opposed to sharing the charge with an adjacent atom, giving that atom (and the whole ion) a negative charge. The ozone molecule contains one oxygen atom that falls under each of these two categories.
Combustion Reactions
Combustion reactions are chemical reactions that involve heating a substance with elemental oxygen, so elemental oxygen is a reactant in every combustion reaction. Some examples of combustion reactions are shown.
Example 2: Metals can be oxidized into cations. One that commonly undergoes oxidation is iron. The chemical equation for the oxidation of iron is shown below:
$$Fe + O_2 \rightarrow Fe_2O_3$$
Here, the iron atoms turn into iron cations, each of which has a \(+3\) charge. The product is iron (III) oxide, otherwise known as rust. We could also balance this equation if we so desired, though it is not necessary to do this to see the oxidation process:
$$4Fe + 3O_2 \rightarrow 2Fe_2O_3$$
The next example involves a hydrocarbon, an organic chemical with only carbon and hydrogen ions.
Example 3: The combustion of any hydrocarbon always results in carbon dioxide and water being formed. In this reaction, the hydrocarbon butane (\(C_4H_{10}\)) is being combusted:
$$C_4H_{10} + O_2 \rightarrow CO_2 + H_2O$$
Again, the atoms of the hydrocarbon get oxidized, and the elemental oxygen gets reduced. This is commonplace for combustion reactions.
Similar to hydrocarbons, carbohydrates are nonmetallic compounds consisting of only carbon, hydrogen, and oxygen. They react in combustion reactions in much the same manner as hydrocarbons.
Oxygen is one of the most special and unique elements that is known to exist. Its properties create interesting patterns in chemistry, as well as in other fields. Many of these are based on its chemical structure and bonding tendencies.
I appreciate that http://www.wolframalpha.com/widgets/view.jsp?id=689aa5a01c216d8b16ed0250cebdc702 provided this Lewis Structure generator for use in this article.