Question

Write the formulas for the following compounds: (a) copper(I) cyanide, (b) strontium chlorite, (c) perbromic acid, (d) hydroiodic acid, (e) disodium ammonium phosphate, (f) potassium dihydrogen phosphate, (g) iodine heptafluoride, (h) tetraphosphorus decasulfide, (i) mercury(II) oxide, (j) mercury(I) iodide, (k) selenium hexafluoride.

Short answer

(a) CuCN, (b) Sr(ClO₂)₂, (c) HBrO₄, (d) HI, (e) Na₂(NH₄)PO₄, (f) KH₂PO₄, (g) IF₇, (h) P₄S₁₀, (i) HgO, (j) Hg₂I₂, (k) SeF₆.

Step-by-step solution

Understanding the Nomenclature

Chemical names provide clues about the structure and composition of compounds. For example, in copper(I) cyanide, the Roman numeral indicates the oxidation state of copper. Prefixes, such as 'di-' or 'tetra-', specify the number of atoms in carbon compounds. Let's break down each name step by step.

Write the Formula for Copper(I) Cyanide

Copper(I) has a charge of +1 (Cu⁺). Cyanide is a polyatomic ion with a charge of -1 (CN⁻). Because both have opposite and equal charges, the formula is simply one copper ion paired with one cyanide ion: CuCN.

Write the Formula for Strontium Chlorite

Strontium is an alkaline earth metal with a charge of +2 (Sr²⁺). Chlorite is a polyatomic ion with a charge of -1 (ClO₂⁻). To balance the charges, two chlorite ions are needed for every strontium ion, resulting in the formula Sr(ClO₂)₂.

Write the Formula for Perbromic Acid

Perbromic acid is an oxyacid with the formula derived from the most oxidized form of bromine, which is in the 'per-' prefix chloric group. It is analogous to perchloric acid, and its formula is HBrO₄.

Write the Formula for Hydroiodic Acid

Hydroiodic acid is a binary acid comprising hydrogen and iodine. As a strong acid, its formula is HI.

Write the Formula for Disodium Ammonium Phosphate

Ammonium is NH₄⁺, phosphate is PO₄³⁻. Disodium means two sodium ions (Na⁺) are involved. Combining them, the formula is Na₂(NH₄)PO₄.

Write the Formula for Potassium Dihydrogen Phosphate

Potassium is K⁺, and dihydrogen phosphate is H₂PO₄⁻. The compound has equal charges, so the formula is KH₂PO₄.

Write the Formula for Iodine Heptafluoride

The prefix 'hepta-' indicates seven fluorine atoms are bonded to iodine, leading to the molecular formula IF₇.

Write the Formula for Tetraphosphorus Decasulfide

The prefixes 'tetra-' and 'deca-' indicate the numbers four and ten, respectively. Therefore, the chemical formula is P₄S₁₀.

Write the Formula for Mercury(II) Oxide

Mercury(II) refers to Hg²⁺. Oxide indicates O²⁻, and they combine in a 1:1 ratio to create the formula HgO.

Write the Formula for Mercury(I) Iodide

Mercury(I) typically pairs up into a diatomic ion (Hg₂)²⁺. With iodide being I⁻, the entire compound becomes Hg₂I₂.

Write the Formula for Selenium Hexafluoride

The 'hexa-' prefix indicates six fluorine atoms. Selenium with six fluorine atoms results in the formula SeF₆.

Key concepts

Ionic Compounds

Ionic compounds form when metals exchange electrons with nonmetals. These exchanged electrons result in the formation of charged atoms, called ions. In ionic compounds, the positive ions (cations) and negative ions (anions) attract one another to create stable structures through ionic bonds.
When naming ionic compounds, the metal's name is followed by the nonmetal's name, often with an ending change to '-ide.' For example, in sodium chloride, the metal sodium forms a cation ( ext{Na}^+) and chloride refers to the anion ( ext{Cl}^-).

• A predictable pattern is that metal ions get their name directly, while nonmetals typically transform their names.
• If a metal can form ions with different charges, Roman numerals indicate the specific charge.

Understanding these patterns makes writing formulas and recognizing compounds straightforward.

Polyatomic Ions

Polyatomic ions are combinations of more than one atom that collectively carry a charge. Instead of being simple diatomic ions like chlorine or fluorine, these ions consist of multiple elements bonded together.
Common examples include sulfate ( ext{SO}_4^{2-}), nitrate ( ext{NO}_3^-), and ammonium ( ext{NH}_4^+). To name compounds with polyatomic ions, simply use the name of the polyatomic ion.

• For instance, in calcium carbonate ( ext{CaCO}_3), calcium is the cation, and carbonate is the polyatomic ion.
• Polyatomic ions can combine with other ions to form neutral compounds.

Mastering polyatomic ions' nomenclature simplifies chemical equation creation and balances reactions.

Oxidation States

Oxidation states provide crucial information about the electron distribution within a compound. They help chemists determine how electrons are being lost or gained in reactions.
Each element in a compound has an oxidation number, which reflects either the electrons an atom shares or exchanges. For free elements, the oxidation state is zero. For ions, it's equivalent to the charge of the ion.

• For example, in ext{Fe}^3+, the oxidation state of iron is +3.
• In the compound ext{NaCl}, the oxidation state of sodium ( ext{Na}^+) is +1, and for chlorine ( ext{Cl}^-), it is -1.

Understanding oxidation states is vital for identifying redox reactions and understanding compound behavior.

Oxyacids

Oxyacids are acids that contain hydrogen, oxygen, and another element. They are an important class of acids in chemistry. The naming of oxyacids varies depending on the oxidation state of the central atom and the number of oxygen atoms present.
These acids are named by modifying the parent ion's name:

• If the polyatomic ion ends in '-ate,' the acid name will end in '-ic.' For example, sulfate becomes sulfuric acid ( ext{H}_2 ext{SO}_4).
• If the polyatomic ion ends in '-ite,' the acid name will change to '-ous.' Chlorite forms chlorous acid.

Oxyacids often act as sources of protons or hydrogen ions in solutions, making them essential in various reactions and industrial applications.