Problem 34 - Chemistry: The Central Science

Question

Write the chemical formula for each of the following, and indicate the oxidation state of the halogen or noble-gas atom in each, (a) calcium hypobromite, (b) bromic acid, (c) xenon trioxide, (d) perchlorate ion, (e) iodous acid, (f) iodine pentafluoride.

Step-by-Step Solution

Answer

The chemical formulas and oxidation states for the given compounds are: (a) Calcium hypobromite: \(Ca(BrO)_2\), bromine oxidation state: \(+1\) (b) Bromic acid: \(HBrO_3\), bromine oxidation state: \(+5\) (c) Xenon trioxide: \(XeO_3\), xenon oxidation state: \(+6\) (d) Perchlorate ion: \(ClO_4^-\), chlorine oxidation state: \(+7\) (e) Iodous acid: \(HIO_2\), iodine oxidation state: \(+3\) (f) Iodine pentafluoride: \(IF_5\), iodine oxidation state: \(+5\)

Step 1: (a) Calcium hypobromite

Calcium is present as its ion Ca²⁺ (from the periodic table), and hypobromite is a polyatomic ion with the symbol BrO⁻ and oxidation state equal to -1. To make an electrically neutral compound: Ca²⁺ + 2BrO⁻ → Ca(BrO)₂ So, the chemical formula is Ca(BrO)₂, and the oxidation state of bromine in hypobromite is +1.

Step 2: (b) Bromic acid

The H⁺ ion from the acid combines with the bromate ion (BrO₃⁻) with -1 oxidation state. H⁺ + BrO₃⁻ → HBrO₃ The chemical formula is HBrO₃, and the oxidation state of bromine is +5.

Step 3: (c) Xenon trioxide

In this compound, xenon is combined with three oxygen atoms with a -2 oxidation state. Xe + 3O²⁻ → XeO₃ The chemical formula is XeO₃, and the oxidation state of xenon is +6.

Step 4: (d) Perchlorate ion

Perchlorate is a polyatomic ion with the symbol ClO₄⁻, with a -1 oxidation state. Since it's already an ion, the formula is ClO₄⁻, and the oxidation state of chlorine is +7.

Step 5: (e) Iodous acid

The H⁺ ion from the acid combines with the iodite ion (IO₂⁻) with -1 oxidation state. H⁺ + IO₂⁻ → HIO₂ The chemical formula is HIO₂, and the oxidation state of iodine is +3.

Step 6: (f) Iodine pentafluoride

In this compound, iodine is combined with five fluorine atoms with a -1 oxidation state. I + 5F⁻ → IF₅ The chemical formula is IF₅, and the oxidation state of iodine is +5.

Key Concepts

Chemical Formulas

Chemical formulas represent how atoms combine to form compounds. They use chemical symbols and numbers to show the actual number of atoms.
For example, in the formula Ca(BrO)₂:

• "Ca" stands for calcium,
• "BrO" represents hypobromite, and
• the subscript '2' indicates there are two hypobromite ions for each calcium ion.

These formulas are built following specific rules to ensure that compounds are electrically neutral. This means that the total positive charge must balance the total negative charge.
In calcium hypobromite: - Calcium has a charge of +2 as it is in Group 2 of the periodic table, meaning it loses two electrons. - Hypobromite has a charge of -1. Therefore, two hypobromite ions are needed to balance one calcium ion.

Halogens

Halogens are elements found in Group 17 of the periodic table. These include fluorine, chlorine, bromine, iodine, and astatine.
Halogens are highly reactive and have seven valence electrons, making them eager to gain one electron to achieve a stable octet configuration.
They commonly form compounds by either gaining an electron, achieving a -1 oxidation state or participating in other oxidation states when forming compounds with oxygen.
For example, in bromic acid (HBrO₃): - Bromine is in an oxidation state of +5. This happens because it is bonded with oxygen, which is highly electronegative and attracts electrons.
Whenever working with halogens, always consider how their reactivity and electronegativity influence the compounds they form.

Noble Gases

Noble gases are located in Group 18 of the periodic table, which includes helium, neon, argon, krypton, xenon, and radon. They are known for having complete outer electron shells, making them extremely stable and mostly unreactive.
However, xenon can form compounds under certain conditions due to its relatively larger atomic size and polarizability compared to other noble gases.
A classic example is xenon trioxide (XeO₃), where xenon has an oxidation state of +6 by sharing electrons with oxygen atoms.

• This challenges the general notion that noble gases do not form compounds, showcasing the exceptions under the right circumstances.

Understanding the unique behavior of noble gases helps in comprehending their role in chemical bonding.

Polyatomic Ions

A polyatomic ion consists of two or more atoms bonded together that function as a single charged entity.
They include ions such as nitrate (NO₃⁻), sulfate (SO₄²⁻), and perchlorate (ClO₄⁻).
In these ions:

• The overall charge comes from the sum of charges of all the atoms within the ion.
• They carry either a positive or negative charge, influencing how they combine with other ions.

For instance, the perchlorate ion (ClO₄⁻) is formed of one chlorine atom bonded with four oxygen atoms, holding a -1 charge.
The oxidation state of chlorine here is +7, determined by the need to balance the highly electronegative oxygen atoms. Recognizing these ions is essential to mastering chemical equations and reactions.