Question

Write formulas for the compounds: (a) aluminum sulfate; (b) ammonium dichromate; (c) silicon tetrafluoride; (d) iron(III) oxide; (e) tricarbon disulfide; (f) cobalt(II) nitrate; (g) strontium nitrite; (h) hydrobromic acid; (i) iodic acid; (j) phosphorus dichloride trifluoride.

Short answer

(a) $A{l}_2(S{O}_4{)}_3$; (b) $(N{H}_4{)}_{2}C{r}_2{O}_7$; (c) $Si{F}_4$; (d) $F{e}_2{O}_3$; (e) $C_3{S}_2$; (f) $Co(N{O}_3{)}_2$; (g) $Sr(N{O}_2{)}_2$; (h) $HBr$; (i) $HI{O}_3$; (j) $PC{l}_2{F}_3$

Step-by-step solution

Writing Formulas for compounds with metallic and nonmetallic ions

Locate the position of the element in the periodic table, determine the charge, and then use the reverse of the rules for writing the name of an ionic compound from its formula to get: (a) aluminum sulfate becomes $A{l}_2(S{O}_4{)}_3$; (b) ammonium dichromate turns into $(N{H}_4{)}_{2}C{r}_2{O}_7$; (d) iron(III) oxide turns into $F{e}_2{O}_3$; (f) cobalt(II) nitrate transforms into $Co(N{O}_3{)}_2$; (g) strontium nitrite converts to $Sr(N{O}_2{)}_2$.

Writing Formulas for binary molecular compounds

Apply the rules for naming binary molecular compounds reversed. In this way: (c) silicon tetrafluoride becomes $Si{F}_4$; (e) tricarbon disulfide turns into $C_3{S}_2$; (j) phosphorus dichloride trifluoride becomes $PC{l}_2{F}_3$.

Writing Formulas for acids

For acids, recognize the name of the anion appended with -ic and prepend with hydro- if it's a binary acid. Hence, (h) hydrobromic acid becomes $HBr$; (i) iodic acid turns into $HI{O}_3$.

Key concepts

Ionic Compounds

Ionic compounds are fascinating substances formed from the attraction between cations and anions. These compounds typically consist of metals bonded to nonmetals. When writing chemical formulas for ionic compounds, the key is to balance the total positive and negative charges. This means that the charges from the metal ions (cations) must cancel out the charges from the nonmetal ions (anions) to create a neutral compound.

• For example, when writing the formula for aluminum sulfate, recognize aluminum (Al) is a metal with a +3 charge, while the sulfate ion (SO₄) has a -2 charge.
• To balance, multiply aluminum by two and sulfate by three to arrive at the neutral compound formula: $A{l}_2(S{O}_4{)}_3$.

This balancing act is what allows ionic compounds to maintain electrical neutrality, a fundamental principle in chemistry.

Molecular Compounds

Molecular compounds, also called covalent compounds, are formed by sharing electrons between nonmetals. These compounds are typically composed of two or more nonmetal elements, and their bonds are created through electron sharing rather than transfer, as seen in ionic compounds. When dealing with molecular compounds, prefixes are often used in their names to denote the number of each atom present.

• The name "silicon tetrafluoride" indicates one silicon and four fluorine atoms, leading to the formula $Si{F}_4$.
• "Tricarbon disulfide" suggests three carbons and two sulfurs, resulting in $C_3{S}_2$.

The use of prefixes like "tetra-" and "di-" in naming molecular compounds helps identify the specific number of atoms involved in the molecule.

Acid Nomenclature

Acids are a special category of compounds characterized by their ability to donate protons (hydrogen ions, $H^{+}$) when dissolved in water. In acid nomenclature, the name gives clues about the formula. Binary acids, which consist of hydrogen and one other element, have names that start with "hydro-" and end with "-ic."

• For instance, hydrobromic acid's name suggests the presence of hydrogen and bromine, resulting in $HBr$.

Oxyacids, which involve hydrogen, oxygen, and another element, are named based on the polyatomic anion they contain. For example, iodic acid, containing the iodate ion $I{O}_3^{-}$, has the formula $HI{O}_3$.
Understanding acid naming conventions can simplify the process of writing chemical formulas for acids.

Periodic Table

The periodic table is an indispensable resource in chemistry, providing a wealth of information about elements and their tendencies to form certain types of compounds. Elements are arranged by increasing atomic number and grouped into columns that signify similar chemical behaviors. These properties are crucial when determining the charges ions take on when forming compounds.

• Metals, typically found on the left side and center of the table, usually form cations by losing electrons.
• Nonmetals, located on the right side, generally gain electrons to become anions.

Knowing an element's position on the periodic table can help predict its chemical behavior and ease the formulation of compounds, whether they're ionic or molecular.

Anion

Anions are negatively charged ions formed when atoms gain electrons. These are mostly nonmetals found on the right side of the periodic table. Anions play critical roles in both ionic and molecular compounds.

• In ionic compounds, anions bond with cations to produce balanced, neutral compounds.
• In molecular compounds, anions can be part of polyatomic ions, which are ions made up of two or more atoms.

Consider the sulfate ion (SO₄²⁻) used in compounds like aluminum sulfate, or the iodate ion (IO₃⁻) found in iodic acid. Understanding anions is key to deciphering chemical formulas and predicting molecular behavior.