chemistry

Oxygen compounds

Oxygen compounds is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Oxygen compounds rather than just read about it. In short: The oxidation state of oxygen is −2 in almost all known compounds of oxygen. The oxidation state −1 is found in a few compounds such as peroxides.

Key takeaways

Oxygen compounds belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Oxygen compounds to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Oxygen compounds from memory before moving on to harder problems.

Reference excerpt

The oxidation state of oxygen is −2 in almost all known compounds of oxygen. The oxidation state −1 is found in a few compounds such as peroxides. Compounds containing oxygen in other oxidation states are very uncommon: −1⁄2 (superoxides), −1⁄3 (ozonides), 0 (elemental, hypofluorous acid), +1⁄2 (dioxygenyl), +1 (dioxygen difluoride), and +2 (oxygen difluoride). Oxygen is reactive and will form oxides with all other elements except the noble gases helium, neon, argon and krypton.

Oxides Water (H2O) is the oxide of hydrogen and most familiar oxygen compound. Its bulk properties partly result from the interaction of its component atoms, oxygen and hydrogen, with atoms of nearby water molecules. Hydrogen atoms are covalently bonded to oxygen in a water molecule but also have an additional attraction (about 23.3 kJ·mol−1 per hydrogen atom) to an adjacent oxygen atom in a separate molecule. These hydrogen bonds between water molecules hold them approximately 15% closer than what would be expected in a simple liquid with just Van der Waals forces.

Due to its electronegativity, oxygen forms chemical bonds with almost all other free elements at elevated temperatures to give corresponding oxides. However, some elements, such as iron which oxidises to iron oxide, or rust, Fe2O3, readily oxidise at standard conditions for temperature and pressure (STP). The surface of metals like aluminium and titanium are oxidized in the presence of air and become coated with a thin film of oxide that passivates the metal and slows further corrosion. So-called noble metals, such as gold and platinum, resist direct chemical combination with oxygen, and substances like gold(III) oxide (Au2O3) must be formed by an indirect route. The alkali metals and alkali earth metals all react spontaneously with oxygen when exposed to dry air to form oxides, and form hydroxides in the presence of oxygen and water. As a result, none of these elements is found in nature as a free metal. Caesium is so reactive with oxygen that it is used as a getter in vacuum tubes. Although solid magnesium reacts slowly with oxygen at STP, it is capable of burning in air, generating very high temperatures, and its metal powder may form explosive mixtures with air. Oxygen is present as compounds in the atmosphere in trace quantities in the form of carbon dioxide (CO2) and oxides of nitrogen (NOx). The Earth's crustal rock is composed in large part of oxides of silicon (silica SiO2, found in granite and sand), aluminium (aluminium oxide Al2O3, in bauxite and corundum), iron (iron(III) oxide Fe2O3, in hematite and rust) and other oxides of metals.

Other inorganic compounds

The rest of the Earth's crust is formed also of oxygen compounds, most importantly calcium carbonate (in limestone) and silicates (in feldspars). Water-soluble silicates in the form of Na4SiO4, Na2SiO3, and Na2Si2O5 are used as detergents and adhesives. Peroxides retain some of oxygen's original molecular structure (−O−O−). White or light yellow sodium peroxide (Na2O2) is formed when metallic sodium is burned in oxygen. Each oxygen atom in its peroxide ion may have a full octet of 4 pairs of electrons. Superoxides are a class of compounds that are very similar to peroxides, but with just one unpaired electron for each pair of oxygen atoms (O−2). These compounds form by oxidation of alkali metals with larger ionic radii (K, Rb, Cs). For example, potassium superoxide (KO2) is an orange-yellow solid formed when potassium reacts with oxygen. Hydrogen peroxide (H2O2) can be produced by passing a volume of 96% to 98% hydrogen and 2 to 4% oxygen through an electric discharge. A more commercially-viable method is to allow autoxidation of an organic intermediate, 2-ethylanthrahydroquinone dissolved in an organic solvent, to oxidize to H2O2 and 2-ethylanthraquinone. The 2-ethylanthraquinone is then reduced and recycled back into the process. When dissolved in water, many metallic oxide form alkaline solutions, while many oxides of nonmetals form acidic solutions. For example, sodium oxide in solution forms the strong base sodium hydroxide, while phosphorus pentoxide in solution forms phosphoric acid. Oxygenated anions such as chlorates (ClO−3), perchlorates (ClO−4), chromates (CrO2−4), dichromates (Cr2O2−7), permanganates (MnO−4), and nitrates (NO−3) are strong oxidizing agents. Oxygen forms heteropoly acids and polyoxometalate ions with tungsten, molybdenum and some other transition metals, such as phosphotungstic acid (H3PW12O40) and octadecamolybdophosphoric acid (H6P2Mo18O62). Oxygen can form oxides with heavier noble gases xenon and radon, although this needs indirect methods. Even though no oxides of krypton are known, oxygen is able to form covalent bonds with krypton in an unstable compound Kr(OTeF5)2. One unexpected oxygen compound is dioxygenyl hexafluoroplatinate, O+2PtF−6, discovered in studying the properties of platinum hexafluoride (PtF6). A change in color when this compound was exposed to atmospheric air suggested that dioxygen was being oxidized (in turn the difficulty of oxidizing oxygen led to the hypothesis that xenon might be oxidized by PtF6, resulting in discovery of the first xenon compound xenon hexafluoroplatinate Xe+PtF−6). The cations of oxygen are formed only in the presence of stronger oxidants than oxygen, which limits them to the action of fluorine and certain fluorine compounds. Simple oxygen fluorides are known.

… excerpt ends here. Continue reading the full article.

Illustrations

Oxygen compounds: Water (H2O) is the most familiar oxygen compound — Water (H2O) is the most familiar oxygen compound

Worked examples

Example 1 — a first encounter with Oxygen compounds

Start with the simplest possible case. Write down what Oxygen compounds claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Oxygen compounds before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Oxygen compounds ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Oxygen compounds

In research: Oxygen compounds appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Oxygen compounds in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Oxygen compounds is common in secondary-school and first-year university syllabi. It links to neighbouring topics Chemical compounds by element, Oxygen compounds, so understanding it makes those chapters shorter.
In everyday life: Look for Oxygen compounds outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Oxygen compounds in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Oxygen compounds means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Oxygen compounds out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Oxygen compounds in simple terms?

The oxidation state of oxygen is −2 in almost all known compounds of oxygen. The oxidation state −1 is found in a few compounds such as peroxides.

Why does Oxygen compounds matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Oxygen compounds?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Oxygen compounds.