Question

Give the Lewis structure of (a) the strongest oxoacid of bromine. (b) a hydrogen compound of nitrogen in which there is an \(-\mathrm{N}-\mathrm{N}-\) bond. (c) an acid added to cola drinks.

Short answer

Answer: (a) HBrO4 (perbromic acid) has a Lewis structure with a central Br atom double bonded to one O atom and single bonded to the other three O atoms. The H atom is bonded to one of the single-bonded O atoms as a hydroxyl group. (b) N2H4 (hydrazine) has a Lewis structure with an N-N single bond at the center and each nitrogen atom bonded to two hydrogen atoms. There is also a lone pair of electrons on each nitrogen atom. (c) H3PO4 (phosphoric acid) has a Lewis structure with a central P atom double bonded to one O atom, and single bonded to two other O atoms, each of which is bonded to an H atom (forming two OH groups).

Step-by-step solution

(a) Finding the strongest oxoacid of bromine

To find the strongest oxoacid of bromine, we need to identify the compound that has the highest number of oxygen atoms bonded to a single bromine atom. The strongest oxoacid of bromine is HBrO4, also known as perbromic acid.

(a) Drawing the Lewis structure of HBrO4

To draw the Lewis structure of HBrO4 (perbromic acid), follow these steps: 1. Count the total number of valence electrons: Br has 7 valence electrons, H has 1, and each O atom has 6. So, there is a total of 7 + 1 + 4(6) = 32 valence electrons. 2. Place the least electronegative atom in the center, which is Br in this case. 3. Arrange the surrounding atoms (H and four O atoms) around the central atom. 4. Draw single covalent bonds between the central atom and the surrounding atoms, and subtract 2 electrons for each bond from the total valence electrons: 32 - 5(2) = 22. 5. Distribute the remaining 22 electrons (as lone pairs) among the surrounding atoms to satisfy the octet rule for each of the O atoms. 6. Assign formal charges to each atom and adjust the bonding, if necessary. The resulting Lewis structure has the bromine atom double bonded to one of the oxygen atoms and single bonded to the other three oxygen atoms. The hydrogen atom is bonded to one of the single-bonded oxygen atoms as a hydroxyl group. The structure is now complete.

(b) Finding the hydrogen compound of nitrogen with an N-N bond

The hydrogen compound of nitrogen in which there is an N-N bond is hydrazine, with the molecular formula N2H4.

(b) Drawing the Lewis structure of N2H4 (hydrazine)

To draw the Lewis structure of N2H4, follow these steps: 1. Count the total number of valence electrons: Each N atom has 5 valence electrons, and each H atom has 1. So there is a total of 2(5) + 4(1) = 14 valence electrons. 2. Place the N atoms next to each other as they will form the N-N bond. 3. Arrange the H atoms around the nitrogen atoms. 4. Draw single covalent bonds, and distribute the remaining electrons as lone pairs. Each nitrogen atom will have a lone pair, and the octet rule will be satisfied for all atoms.

(c) Finding the acid added to cola drinks

The acid added to cola drinks is phosphoric acid, with the molecular formula H3PO4.

(c) Drawing the Lewis structure of H3PO4 (phosphoric acid)

To draw the Lewis structure of H3PO4, follow these steps: 1. Count the total number of valence electrons: P has 5 valence electrons, each O atom has 6, and each H atom has 1. So there's a total of 5 + 3(6) + 3(1) = 32 valence electrons. 2. Place the central atom P in the center, and arrange the surrounding O atoms and H atoms around it. 3. Draw single covalent bonds between the central atom and the surrounding atoms, then distribute the remaining electrons as lone pairs. The final Lewis structure has one double bond between P and one O atom, with two other O atoms each bonded to H atoms (forming two OH groups) and single bonded to the central P atom.

Key concepts

Oxoacid of Bromine

Understanding oxoacids of bromine requires a grasp of their atomic compositions and bonding structures. Oxoacids contain hydrogen, oxygen, and another element, which in this case is bromine. The 'strongest' oxoacid refers to the compound with the greatest ability to donate protons (H⁺ ions), commonly having the highest number of oxygen atoms.

In the case of bromine, the strongest oxoacid is perbromic acid, with the chemical formula HBrO₄. To depict the arrangement of the atoms, we follow the steps provided in the textbook solution to create a Lewis structure. The Lewis structure is a diagram that shows the bonding between atoms of a molecule and the lone pairs of electrons that may exist. For HBrO₄, bromine is surrounded by four oxygen atoms. The structural representation showcases one bromine (Br) central atom double-bonded with an oxygen (O) and single-bonded to three other oxygens, with one of those single-bonded oxygens also bound to a hydrogen (H) atom. This arrangement reflects the bond distribution and octet rule compliance for a stable configuration.

Hydrogen Compound of Nitrogen

The exercise brings us to explore hydrogen compounds of nitrogen that feature an N-N bond. These types of compounds frequently engage in a vast array of chemical reactions due to the properties of nitrogen. Hydrazine (N₂H₄) is a straightforward example that includes an N-N bond.

The Lewis structure for hydrazine helps us understand the bonds that form between nitrogen atoms and hydrogen. In the Lewis structure, each nitrogen atom is bonded to two hydrogen atoms, and a single bond connects the two nitrogen atoms, satisfying the octet rule. A distinctive characteristic of the N-N bond in hydrazine is its ability to contribute to the molecule's relatively high energy, making it useful in rocket propulsion and other applications. Through careful counting and placement of valence electrons as described in the textbook solution, the interconnected nature of the nitrogen and hydrogen in this compound is depicted.

Acid in Cola Drinks

The familiar tangy taste of cola drinks partly comes from the addition of an acid. In particular, phosphoric acid (H₃PO₄) is commonly used to provide a distinctive flavor and to preserve freshness. Phosphoric acid is an example of a non-volatile acid, which means it doesn't easily evaporate at room temperature thus maintaining the flavor profile of the drink over time.

The Lewis structure of phosphoric acid illustrates the electron arrangement and phosphate (PO₄) bonds. According to the solution steps, phosphoric acid includes a phosphorus (P) atom at the center, surrounded by four oxygen (O) atoms, with three of those oxygens bound to a hydrogen (H) atom. The depiction reveals a double bond between phosphorus and one of the oxygen atoms, with single bonds to the remaining oxygens and OH groups. This structure, with its blend of covalent bonds and lone pairs, is crucial for the stability of phosphoric acid, which enhances the taste and preservative qualities of cola drinks.