Question

Name the following compounds: (a) \(\mathrm{KH}_{2} \mathrm{PO}_{4}\), (b) \(\mathrm{K}_{2} \mathrm{HPO}_{4},\) (c) HBr (gas), (d) HBr (in water), (e) \(\mathrm{Li}_{2} \mathrm{CO}_{3},\) (f) \(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7},(\mathrm{~g}) \mathrm{NH}_{4} \mathrm{NO}_{2},(\mathrm{~h}) \mathrm{HIO}_{3}\), (1) \(\mathrm{SrSO}_{4},(\mathrm{~m}) \mathrm{Al}(\mathrm{OH})_{3}\) (i) \(\mathrm{PF}_{5},(\mathrm{j}) \mathrm{P}_{4} \mathrm{O}_{6},(\mathrm{k}) \mathrm{CdI}_{2}\)

Short answer

(a) Potassium dihydrogen phosphate, (b) Dipotassium hydrogen phosphate, (c) Hydrogen bromide, (d) Hydrobromic acid, (e) Lithium carbonate, (f) Potassium dichromate, (g) Ammonium nitrite, (h) Iodic acid, (i) Phosphorus pentafluoride, (j) Tetraphosphorus hexoxide, (k) Cadmium iodide, (1) Strontium sulfate, (m) Aluminum hydroxide.

Step-by-step solution

Identifying Ionic Compounds

To name ionic compounds like \( \mathrm{KH}_2\mathrm{PO}_4 \) and \( \mathrm{K}_2\mathrm{HPO}_4 \), recognize the cation (potassium, \( \mathrm{K^+} \)) and the anion. For \( \mathrm{KH}_2\mathrm{PO}_4 \), the anion is dihydrogen phosphate (\( \mathrm{H_2PO_4^-} \)), and for \( \mathrm{K}_2\mathrm{HPO}_4 \), it's hydrogen phosphate (\( \mathrm{HPO_4^{2-}} \)). Thus, the names are potassium dihydrogen phosphate and dipotassium hydrogen phosphate, respectively.

Recognizing Molecular and Acid Names

Recognize molecular compounds and acids. \( \mathrm{HBr} \) as a gas is called hydrogen bromide. When \( \mathrm{HBr} \) is dissolved in water, it becomes an acid known as hydrobromic acid.

Carbonates and Chromates

For \( \mathrm{Li}_2\mathrm{CO}_3 \), identify lithium (cation) and carbonate (anionic group) which results in the name lithium carbonate. Similarly, for \( \mathrm{K}_2\mathrm{Cr}_2\mathrm{O}_7 \), identify potassium (cation) and dichromate (anion), giving the name potassium dichromate.

Naming Miscellaneous Ionic Compounds

\( \mathrm{NH}_4 \mathrm{NO}_2 \) involves the ammonium cation and the nitrite anion, hence it is named as ammonium nitrite. \( \mathrm{HIO}_3 \) is an acid and is called iodic acid.

Sulfate and Hydroxide Naming

\( \mathrm{SrSO}_4 \) consists of strontium (cation) and sulfate (anion), named strontium sulfate. \( \mathrm{Al(OH)}_3 \) involves aluminum (cation) and hydroxide groups, thus, it is called aluminum hydroxide.

Covalent Compounds and Halides

For \( \mathrm{PF}_5 \), the name is phosphorus pentafluoride due to the covalent bonding nature and the prefix indicating the number of fluorides. \( \mathrm{P}_4\mathrm{O}_6 \) is named tetraphosphorus hexoxide reflecting the covalent nature and prefixes. Finally, \( \mathrm{CdI}_2 \) is simply named cadmium iodide after its ionic components.

Key concepts

Ionic Compounds

Ionic compounds are formed when metals and non-metals transfer electrons to form ions, creating a cation and an anion. These compounds are electrically neutral because the total positive charge of the cations equals the total negative charge of the anions. To name these compounds, first identify the metal, which acts as the cation, followed by the non-metal part, often a polyatomic ion as an anion. For example, in the compound \( \text{K}_2\text{HPO}_4 \), potassium (\( \text{K}^+ \)) is the cation, and hydrogen phosphate (\( \text{HPO}_4^{2-} \)) is the anion. Consequently, the compound is named dipotassium hydrogen phosphate. Similarly, \( \text{Li}_2\text{CO}_3 \) sees lithium (\( \text{Li}^+ \)) as the cation and carbonate (\( \text{CO}_3^{2-} \)) as the anion, resulting in the name lithium carbonate.
Look for the metals and determine the charge to name the ionic compound effectively. Remember, transition metals can have multiple charges, so their ionic charge may be indicated in roman numerals, though this is not always necessary for metals like potassium and lithium.
Naming ionic compounds requires understanding which parts are the cation and the anion, and ensuring you recognize any polyatomic ions involved.

Molecular Compounds

Molecular compounds are created when non-metals share electrons, resulting in covalent bonds. These compounds are named differently from ionic compounds using prefixes to indicate the number of each element present in the compound. Common prefixes include mono-, di-, tri-, tetra-, penta-, and hexa-.
For instance, \( \text{PF}_5 \) is phosphorus pentafluoride. Here "penta-" signifies the presence of five fluoride atoms bonded to one phosphorus atom. For another example, \( \text{P}_4\text{O}_6 \) is named tetraphosphorus hexoxide. The prefix "tetra-" indicates four phosphorus atoms, while "hexa-" indicates six oxygen atoms.
Understanding the basic prefix guidelines helps in naming molecular compounds accurately and articulates the components and their numbers clearly. Always start with the least electronegative element when naming molecular compounds (except when hydrogen is present) and use the appropriate prefixes to denote the quantities of each element.

Acid Naming

Acids are special types of compounds that release \( \text{H}^+ \) ions when dissolved in water. Naming acids depends on the anion they contain. When the anion ends in "-ide," the acid name starts with "hydro-" and ends with "-ic." For example, \( \text{HBr} \) as an acid is called hydrobromic acid because "bromide" transforms into "bromic." However, when \( \text{HBr} \) is not in solution, it is referred to as hydrogen bromide.
If the anion ends in "-ate," the acid name uses the suffix "-ic," like \( \text{HIO}_3 \) becoming iodic acid. Words ending in "-ite" change to "-ous," but this naming pattern doesn't apply in the current exercise.
It is crucial to identify if the compound is gaseous or aqueous because that affects the naming convention. Remember to convert the anion's ending into the correct suffix and include prefixes when essential.

Polyatomic Ions

Polyatomic ions are ions composed of two or more atoms covalently bonded, acting as a single charged entity. These ions often appear in ionic compounds and are crucial in naming them correctly. They can have positive or negative charges, with most being anions.
Familiarity with common polyatomic ions like sulfate \((\text{SO}_4^{2-})\), nitrate \((\text{NO}_3^-)\), or phosphate \((\text{PO}_4^{3-})\) greatly aids in identifying compounds. For example, knowing \( \text{K}_2\text{Cr}_2\text{O}_7 \) involves the dichromate ion \((\text{Cr}_2\text{O}_7^{2-})\) helps in naming it potassium dichromate.
Polyatomic ions maintain their name across different compounds; recognizing these ions quickly will lead to correctly naming compounds. Understanding these ions' composition and charges also assists in balancing charges within ionic compounds and aids in writing chemical formulas accurately.