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 of the halogen or noble-gas atoms are as follows: (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-by-step solution

Write the chemical formula

Calcium has a +2 charge \((Ca^{2+})\) and hypobromite has a -1 charge \((BrO^{-})\). To balance the charges, we need 2 hypobromite ions for each calcium ion. Therefore, the chemical formula for calcium hypobromite is \(Ca(BrO)_2\).

Determine the oxidation state of the halogen

In hypobromite ion \((BrO^{-})\), the oxidation state of oxygen is always -2. To find the oxidation state of bromine (Br), use the formula of the ion's charge: \[Charge = Oxidation\, state\, of\, Br + Oxidation\, state\, of\, O\] \[(-1) = x + (-2)\] \[x = +1\] So, the oxidation state of bromine in calcium hypobromite is +1. #(b) Bromic acid#

Write the chemical formula

Bromic acid is an oxyacid of bromine, composed of a central bromine atom bonded to one hydroxide group and three oxygen atoms. The chemical formula for bromic acid is \(HBrO_3\).

Determine the oxidation state of the halogen

In \(HBrO_3\), the oxidation state of the hydrogen atom is +1 and the oxidation state of each oxygen atom is -2. Using the formula of the molecule's charge: \[0 = (+1) + x + 3(-2)\] \[0 = 1 + x - 6\] \[x = +5\] So, the oxidation state of bromine in bromic acid is +5. #(c) Xenon trioxide#

Write the chemical formula

Xenon trioxide is composed of one xenon atom bonded to three oxygen atoms. The chemical formula for xenon trioxide is \(XeO_3\).

Determine the oxidation state of the noble-gas atom

In \(XeO_3\), the oxidation state of each oxygen atom is -2. Using the formula of the molecule's charge: \[0 = x + 3(-2)\] \[0 = x - 6\] \[x = +6\] So, the oxidation state of xenon in xenon trioxide is +6. #(d) Perchlorate ion#

Write the chemical formula

Perchlorate ion is an oxyanion of chlorine, composed of a central chlorine atom bonded to four oxygen atoms. The charge of the perchlorate ion is -1. The chemical formula for the perchlorate ion is \(ClO_4^-\).

Determine the oxidation state of the halogen

In the \(ClO_4^-\) ion, the oxidation state of each oxygen atom is -2. Using the formula of the ion's charge: \[(-1) = x + 4(-2)\] \[(-1) = x - 8\] \[x = +7\] So, the oxidation state of chlorine in the perchlorate ion is +7. #(e) Iodous acid#

Write the chemical formula

Iodous acid is an oxyacid of iodine with less oxygen than iodic acid, composed of a central iodine atom bonded to one hydroxide group and one oxygen atom. The chemical formula for iodous acid is \(HIO_2\).

Determine the oxidation state of the halogen

In \(HIO_2\), the oxidation state of the hydrogen atom is +1 and the oxidation state of each oxygen atom is -2. Using the formula of the molecule's charge: \[0 = (+1) + x + 2(-2)\] \[0 = 1 + x - 4\] \[x = +3\] So, the oxidation state of iodine in iodous acid is +3. #(f) Iodine pentafluoride#

Write the chemical formula

Iodine pentafluoride is composed of one iodine atom bonded to five fluorine atoms. The chemical formula for iodine pentafluoride is \(IF_5\).

Determine the oxidation state of the halogen

In \(IF_5\), the oxidation state of each fluorine atom is -1. Using the formula of the molecule's charge: \[0 = x + 5(-1)\] \[0 = x - 5\] \[x = +5\] So, the oxidation state of iodine in iodine pentafluoride is +5.

Key concepts

Chemical Formula

Understanding the chemical formula of a substance is a foundational concept in chemistry that describes the types and numbers of atoms in a molecule. It serves as a type of shorthand that conveys the proportions of different elements in a compound. For example, in calcium hypobromite, the chemical formula is Ca(BrO)_2, which indicates that the compound consists of one calcium ion and two hypobromite ions. The subscript 2 suggests there are two bromine and two oxygen atoms for each calcium ion.

Knowing how to write a chemical formula involves recognizing the charges of ions and how they combine to form neutral compounds. For instance, because calcium has a +2 charge and hypobromite has a -1 charge, two hypobromite ions are needed to balance out the positive charge of one calcium ion. This knowledge is vital not only for predicting chemical reactions but also for understanding the structure and properties of compounds.

Halogens Oxidation States

Halogens are a group of elements that include fluorine, chlorine, bromine, iodine, and astatine. The oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. Halogens typically exhibit a range of oxidation states, from -1 to positive values, depending on the element and compound they are in. For instance, bromine has an oxidation state of +1 in hypobromite (BrO^-) and +5 in bromic acid (HBrO_3).

Determining the oxidation state is crucial for understanding the reactivity and bonding of an element. For halogens, the oxidation state can be figured out by knowing the oxidation states of other atoms in the compound (such as oxygen usually being -2) and applying the rule that the sum of oxidation states in a neutral compound must equal zero, or the charge of the ion for polyatomic ions.

Noble-Gas Chemistry

The field of noble-gas chemistry is relatively young because noble gases were long thought to be inert. However, compounds like xenon trioxide (XeO_3) have been discovered, which reveal that noble gases can form stable compounds under certain conditions. In the case of XeO_3, xenon has an oxidation state of +6.

This shift in understanding has expanded the boundaries of chemistry and allows for the creation of new materials with unique properties. Noble gases tend to form compounds with oxidation states that reflect the number of electrons they can 'gain' or 'lose' to achieve a stable octet configuration – key information for predicting the types of chemical reactions they can undergo.

Oxyanions

Oxyanions are negatively charged polyatomic ions that contain oxygen bonded to another element. They often form as a result of acids dissociating in water. A classic example provided is the perchlorate ion (ClO_4^-), featuring chlorine in its highest oxidation state of +7. The structure of an oxyanion can give insight into the relative electronegativities of its constituent atoms and is pivotal for deducing the geometric structure and reactivity of these ions. The naming convention of oxyanions usually reflects the number of oxygen atoms present: the 'per-' prefix denotes the most oxygen, while ‘-ite’ ending indicates fewer oxygen atoms compared to ‘-ate’.

Oxyacids

Oxyacids are acids that contain hydrogen, oxygen, and at least one other element. The other element, usually a nonmetal, is bonded to the oxygen. An oxyacid molecule will release hydrogen ions when dissolved in water, thereby creating an acidic solution. For instance, iodous acid (HIO_2) contains two oxygen atoms, one iodine, and one hydrogen. Determining the oxidation state of the central atom, like iodine in the given example, follows the same logic as for oxyanions, considering that the overall molecule is neutral. Oxyacids are classified based on the number of oxygen atoms and the oxidation state of the central atom, and these characteristics significantly influence the strength and properties of the acid.