Oxides

Oxide Ion (O²⁻)

The oxygen-containing ion found in ordinary ionic oxides.

O²⁻

Chemical formula and charge of the oxide ion.

−2

What is the oxidation state of oxygen in an ordinary oxide ion?

Peroxide Ion (O₂²⁻)

An oxygen-containing polyatomic ion consisting of two covalently bonded oxygen atoms with an overall charge of 2−.

O₂²⁻

Chemical formula and charge of the peroxide ion.

−1

What is the oxidation state of each oxygen atom in a peroxide ion?

O–O Covalent Single Bond

What type of bond connects the two oxygen atoms in the peroxide ion, O₂²⁻?

1

What is the O–O bond order in the peroxide ion?

Superoxide Ion (O₂⁻)

An oxygen-containing polyatomic ion consisting of two bonded oxygen atoms with an overall charge of 1−.

O₂⁻

Chemical formula and charge of the superoxide ion.

−1/2

What is the average oxidation state of each oxygen atom in the superoxide ion?

1½

What is the O–O bond order in the superoxide ion?

Oxides, Peroxides, and Superoxides

Name the three important categories of representative-metal compounds distinguished by the form of oxygen they contain.

O²⁻, O₂²⁻, O₂⁻

Match the oxygen-containing ions to oxide, peroxide, and superoxide, respectively.

All Representative Metals

Which representative metals form ordinary oxides?

Group 1 and Some Group 2 Metals

Which representative-metal groups are especially important for the formation of peroxides?

Group 1 Metals

Which representative-metal group can form both peroxides and superoxides?

M₂O₂

What is the general formula given for a Group 1 metal peroxide?

MO₂

What is the general formula given for a Group 2 metal peroxide?

MO₂

What is the general formula given for a Group 1 metal superoxide?

The Identity and Charge of the Oxygen Species

Although a Group 2 peroxide and Group 1 superoxide may both have the formula MO₂, what distinguishes the two chemically?

Peroxide Ion (O₂²⁻)

In a Group 2 peroxide with the general formula MO₂, what oxygen species is present?

Superoxide Ion (O₂⁻)

In a Group 1 superoxide with the general formula MO₂, what oxygen species is present?

Heating Metal Hydroxides

One method for preparing many representative-metal oxides is heating the corresponding __________.

Metal Oxide and Water

Heating an appropriate metal hydroxide generally produces what two products?

Metal Hydroxide → Metal Oxide + H₂O

General reaction pattern for producing a metal oxide by thermal decomposition of a hydroxide.

Heating Metal Carbonates

Another common method of preparing representative-metal oxides is heating the corresponding __________.

Metal Oxide and Carbon Dioxide

Heating an appropriate metal carbonate generally produces what two products?

Metal Carbonate → Metal Oxide + CO₂

General reaction pattern for producing a metal oxide by thermal decomposition of a carbonate.

CaCO₃(s) → CaO(s) + CO₂(g)

Chemical equation for the thermal decomposition of calcium carbonate.

Calcium Oxide (CaO)

What solid metal oxide forms when calcium carbonate is strongly heated?

Carbon Dioxide (CO₂)

What gaseous product is released when a metal carbonate such as CaCO₃ thermally decomposes?

Groups 2–15

With the important exception of mercury(II) oxide, oxides of metals in which representative groups can generally be produced by burning the corresponding metals in air?

Mercury(II) Oxide (HgO)

This metal oxide is an important exception to the general preparation of group 2–15 metal oxides by burning the metal in air.

Below 500 °C

Mercury(II) oxide forms slowly when mercury is warmed at temperatures approximately __________.

It Decomposes

What happens to HgO when mercury/mercury oxide is heated to higher temperatures above the conditions favorable for its formation?

Inert Pair Effect

The tendency of the heaviest members of certain groups to favor oxidation states two units below the usual group oxidation state is associated with the __________.

Two Less than the Group Oxidation State

Because of the inert pair effect, the heaviest member of certain groups tends to form an oxide in which the metal oxidation state is __________.

Tl₂O

What oxide forms when thallium burns, illustrating the inert pair effect?

PbO

What oxide forms when lead burns under the behavior described in the lesson, illustrating the inert pair effect?

Bi₂O₃

What oxide forms when bismuth burns, illustrating the inert pair effect?

SnO₂

What oxide forms when tin burns, illustrating the higher group oxidation state favored by the lighter member?

Lighter Members of a Group

The oxides of the __________ generally exhibit the group oxidation state more readily than the heaviest members affected strongly by the inert pair effect.

Groups 1 and 2

Burning metals from which two groups in air is generally NOT a suitable method for obtaining pure ordinary oxides?

Because they can also react with nitrogen and may form peroxides or superoxides.

Why is burning Group 1 and Group 2 metals in air not a reliable method for producing pure ordinary oxides?

Ionic Nitrides

Because Group 1 and Group 2 metals are highly reactive, burning them in air may produce oxides mixed with __________ formed by reaction with atmospheric nitrogen.

Peroxides and Superoxides

In addition to oxides and nitrides, some highly reactive Group 1 and Group 2 metals can form these oxygen-rich products when heated in air.

Potassium Peroxide (K₂O₂)

What oxygen compound of potassium can form under controlled oxygen conditions?

2K(s) + O₂(g) → K₂O₂(s)

Chemical equation showing the formation of potassium peroxide under controlled oxygen conditions.

Potassium Superoxide (KO₂)

What oxygen compound forms when potassium reacts with excess oxygen?

K(s) + O₂(g) → KO₂(s)

Chemical equation showing the formation of potassium superoxide in excess oxygen.

Excess Oxygen

Formation of potassium superoxide, KO₂, is favored when potassium reacts with __________.

Larger Alkali-Metal Cations

Stability of alkali-metal peroxides and especially superoxides generally increases as the metal cation becomes __________.

Down Group 1

As you move __________, the larger alkali-metal ions become increasingly capable of stabilizing peroxide and superoxide ions.

Oxide Ion (O²⁻)

A very powerful hydrogen-ion acceptor found in ionic oxides.

Powerful Hydrogen-Ion Acceptor

Why does the oxide ion O²⁻ display strongly basic behavior?

Acids

Most representative-metal oxides react with __________ to produce salts.

Salt and Water

A basic metal oxide reacting with an acid commonly produces __________ and __________.

Metal Oxide + Acid → Salt + Water

General acid-base reaction pattern for many representative-metal oxides.

Al₂O₃, SnO₂, and PbO₂

Name the three very insoluble representative-metal oxides highlighted as exceptions to the usual acid-reactivity discussion.

Calcium Oxide (CaO)

This basic oxide is commonly known as quicklime and is useful as a base.

Calcium Hydroxide [Ca(OH)₂]

This hydroxide, formed from CaO and water, is useful as a base for accepting protons and neutralizing acids.

CaO(s) + H₂O(l) → Ca(OH)₂(s)

Chemical equation showing the reaction of calcium oxide with water.

Proton Acceptors

CaO and Ca(OH)₂ behave as bases because they ultimately function as __________.

Corundum

The naturally occurring mineral form of Al₂O₃.

Aluminum Oxide (Al₂O₃)

What is the chemical composition of the mineral corundum?

Abrasive

Because corundum is extremely hard, it is used for grinding and polishing as an __________.

Ruby and Sapphire

Which two important gemstones are varieties of corundum?

Chromium

A small amount of which element produces the characteristic red color of ruby?

Impurities

Different __________ incorporated into corundum can produce the wide variety of sapphire colors.

2050 °C

Approximate melting point of aluminum oxide given in the lesson.

Synthetic Ruby Crystals

Ruby lasers use what artificially manufactured crystalline material?

Zinc Oxide (ZnO)

This oxide was historically useful as a white paint pigment and is also important in rubber goods and medicinal products.

Automobile Tires and Other Rubber Goods

ZnO is important in the manufacture of what major class of commercial products?

Nanoparticles

In zinc-oxide-based sunscreens, ZnO is present as extremely small grains known as __________.

Zinc-Oxide-Based Sunscreen

An important modern application of ZnO in which tiny particles help prevent sunburn.

Lead Dioxide (PbO₂)

This oxide is a constituent of charged lead storage batteries.

Lead Storage Batteries

PbO₂ is an important constituent of what type of battery?

Lead(IV) → Lead(II)

Lead dioxide is a strong oxidizing agent partly because lead tends to change from which oxidation state to which more stable oxidation state?

Two Electrons

How many electrons does Pb(IV) gain when it is reduced to Pb(II)?

Powerful Oxidizing Agent

Because Pb(IV) readily gains two electrons to form the more stable Pb(II) state, PbO₂ acts as a __________.

Oxide: O²⁻; Peroxide: O₂²⁻; Superoxide: O₂⁻

Complete the comparison: oxide = _____; peroxide = _____; superoxide = _____.

−2, −1, −1/2

What are the oxidation states of an individual oxygen atom in an oxide, peroxide, and superoxide, respectively?

No O–O Bond, O–O Single Bond, O–O Bond Order 1½

Compare the characteristic oxygen bonding in ordinary oxide ions, peroxide ions, and superoxide ions, respectively.