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.

Short 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: HBrO₂, bromine oxidation state: +3 (c) Xenon trioxide: XeO₃, xenon oxidation state: +6 (d) Perchlorate ion: ClO₄⁻, chlorine oxidation state: +7 (e) Iodous acid: HIO, iodine oxidation state: +1 (f) Iodine pentafluoride: IF₅, iodine oxidation state: +5

Step-by-step solution

(a) Calcium hypobromite formula and oxidation state of bromine

To write the formula for calcium hypobromite, first identify the cation and anion involved. Calcium is the cation and has a charge of +2 (as it is an alkaline earth metal from group 2). Hypobromite is the anion and is formed from bromine and oxygen. The prefix "hypo" and the suffix "ite" signify that there is one less oxygen atom than in the "ite" form. For bromine, "bromite" involves BrO₂⁻, and therefore hypobromite is BrO⁻. The formula for calcium hypobromite is Ca(BrO)₂ (balancing the charges of +2 and -1*2). For oxidation states, let calcium be Ca, bromine be Br and oxygen be O. We have: - Br + O = -1 (overall charge of the hypobromite ion) We know that the oxidation state of O is -2. Therefore: - Br - 2 = -1 - Br = +1 Thus, the oxidation state of bromine in calcium hypobromite is +1.

(b) Bromic acid formula and oxidation state of bromine

Bromic acid has the prefix "ic" and contains an H atom. The "ic" suffix indicates it is derived from bromate (BrO₃⁻) with one less O atom, which is BrO₂⁻. The formula for bromic acid is HBrO₂. To find the oxidation state of bromine, we let H be hydrogen, Br be bromine, and O be oxygen. We then have: - H + Br + 2 * O = 0 (since there is no overall charge) Using the known oxidation states of hydrogen and oxygen: - (+1) + Br + 2 * (-2) = 0 - Br - 3 = 0 - Br = +3 The oxidation state of bromine in bromic acid is +3.

(c) Xenon trioxide formula and oxidation state of xenon

Xenon trioxide is formed by xenon (Xe) and three oxygen (O) atoms. The formula for xenon trioxide is XeO₃. To determine the oxidation state of xenon in this compound, - Xe + 3 * O = 0 (since there is no overall charge) Using the known oxidation state of oxygen: - Xe + 3 * (-2) = 0 - Xe - 6 = 0 - Xe = +6 The oxidation state of xenon in xenon trioxide is +6.

(d) Perchlorate ion formula and oxidation state of chlorine

The perchlorate ion has the prefix "per" and the suffix "ate," meaning it has one more oxygen atom than the "ate" form, which is ClO₄⁻. The formula for the perchlorate ion is ClO₄⁻. To determine the oxidation state of chlorine (Cl) in this ion, - Cl + 4 * O = -1 (overall charge of the perchlorate ion) Using the known oxidation state of oxygen: - Cl + 4 * (-2) = -1 - Cl - 8 = -1 - Cl = +7 The oxidation state of chlorine in the perchlorate ion is +7.

(e) Iodous acid formula and oxidation state of iodine

Iodous acid has the prefix "ous" and contains an H atom. The "ous" suffix indicates it is derived from iodite (IO₂⁻) with one less O atom, which is IO⁻. The formula for iodous acid is HIO. To find the oxidation state of iodine in iodous acid, we let H be hydrogen, I be iodine, and O be oxygen. We then have: - H + I + O = 0 (since there is no overall charge) Using the known oxidation states of hydrogen and oxygen: - (+1) + I + (-2) = 0 - I - 1 = 0 - I = +1 The oxidation state of iodine in iodous acid is +1.

(f) Iodine pentafluoride formula and oxidation state of iodine

Iodine pentafluoride consists of iodine (I) and five fluorine (F) atoms. The formula for iodine pentafluoride is IF₅. To determine the oxidation state of iodine in this compound: - I + 5 * F = 0 (since there is no overall charge) Using the known oxidation state of fluorine (-1): - I + 5 * (-1) = 0 - I - 5 = 0 - I = +5 The oxidation state of iodine in iodine pentafluoride is +5.

Key concepts

Oxidation states

The concept of oxidation states is essential to understand chemical reactions and formulas. An oxidation state essentially gives us an idea of the degree of oxidation (loss of electrons) or reduction (gain of electrons) of an atom in a compound. It is denoted by a number.

For example, in calcium hypobromite (Ca(BrO)₂), the oxidation state of bromine is +1. This indicates that bromine has lost one electron when forming the hypobromite ion (BrO⁻). Usually, oxygen has a common oxidation state of -2, and knowing this helps us deduce the oxidation state of other elements when the total charge of the ion is known.

• Ca (Calcium) has a +2 oxidation state.
• Br (Bromine) in hypobromite has a +1 oxidation state.
• O (Oxygen) almost always exhibits a -2 oxidation state in such compounds.

By totaling the oxidation states of the elements in a compound to the charge of the ion, we can systematically find the unknown oxidation state, providing clarity on the electron exchange in bonding.

Halogens

Halogens are a group of elements found in Group 17 of the periodic table. They include fluorine, chlorine, bromine, iodine, and astatine. These elements are highly reactive non-metals and are well known for forming salts, like sodium chloride (table salt), through ionic bonds with positively charged metals.

In our exercise, bromine and iodine are examples of halogens used in compounds such as bromic acid (HBrO₂) and iodine pentafluoride (IF₅). Halogens typically have seven electrons in their outermost electron shell, making them eager to gain one more electron to achieve a stable octet configuration. However, within compounds, their oxidation states can vary, showing their versatility and complex chemistry. For instance:

• In bromic acid (HBrO₂), bromine has an oxidation state of +3.
• In iodine pentafluoride (IF₅), iodine exhibits an oxidation state of +5.

Understanding halogens' behaviors in different chemical environments is vital for predicting their reactivities and the types of compounds they can form.

Noble gases

Noble gases belong to Group 18 of the periodic table and include helium, neon, argon, krypton, xenon, and radon. These gases are characterized by their full valence electron shells, making them generally inert and very stable. They do not readily form compounds because they do not tend to gain, lose, or share electrons.

However, xenon is a notable exception, as it can form compounds such as xenon trioxide (XeO₃), showing us that even the most stable elements can participate in chemical reactions under the right conditions. In xenon trioxide, xenon has an oxidation state of +6, which means it shares electrons with oxygen atoms in the compound.

• Noble gases are colorless, odorless, and tasteless.
• Most of them exist as monoatomic gases under standard conditions.
• Xenon's capability to form bonds (albeit infrequent) defies the characteristic inertness of noble gases.

The chemistry of xenon demonstrates that while noble gases are largely unreactive, intriguing exceptions exist, expanding our understanding of chemical bonding.

Chemical nomenclature

Chemical nomenclature is the systematic naming of chemical compounds, providing a unique identifier for each substance. It involves using specific rules and conventions established by the International Union of Pure and Applied Chemistry (IUPAC). Understanding these conventions allows us to deduce the chemical composition and structure of a compound from its name and vice versa.

For instance, the name "calcium hypobromite" suggests a compound containing Ca (calcium) and the hypobromite ion (BrO⁻), leading to the chemical formula Ca(BrO)₂. Several conventions used include:

• Prefixes like "hypo," "per," "di," signify the number or relative quantity of atoms, particularly of oxygen, in oxoanions.
• Suffixes like "-ite" and "-ate" indicate different oxidation states or numbers of oxygen atoms.
• "Hydro-" and 'ic/ous' prefixes and suffixes in acids denote hydrogen presence and the oxidation state.

Through familiarity with these rules, we can accurately interpret and conjure the formulas of complex compounds from their names, bridging the gap between theoretical understanding and practical application in chemistry.