Question

Write the chemical formula for each substance mentioned in the following word descriptions (use the front inside cover to find the symbols for the elements you do not know). (a) Zinc carbonate can be heated to form zinc oxide and carbon dioxide. (b) On treatment with hydrofluoric acid, silicon dioxide forms silicon tetrafluoride and water. (c) Sulfur dioxide reacts with water to form sulfurous acid. (d) The substance phosphorus trihydride, commonly called phosphine, is a toxic gas. (e) Perchloric acid reacts with cadmium to form cadmium(II) perchlorate. (f) Vanadium(II) bromide is a colored solid.

Short answer

(a) ZnCO3 → ZnO + CO2 (b) HF + SiO2 → SiF4 + H2O (c) SO2 + H2O → H2SO3 (d) PH3 (e) HClO4 + Cd → Cd(ClO4)2 (f) VBr2

Step-by-step solution

Identify the chemical elements

By reading the description, we can identify the chemical elements involved: Zinc, Carbon, and Oxygen.

Write the chemical formula

Following the rules of chemical nomenclature for ionic compounds, we have: Zinc carbonate (ZnCO3) can be heated to form zinc oxide (ZnO) and carbon dioxide (CO2). (b) On treatment with hydrofluoric acid, silicon dioxide forms silicon tetrafluoride and water.

Identify the chemical elements

We can identify the chemical elements involved: Silicon, Oxygen, Hydrogen, and Fluorine.

Write the chemical formula

Following the rules of chemical nomenclature for molecular compounds, we have: On treatment with hydrofluoric acid (HF), silicon dioxide (SiO2) forms silicon tetrafluoride (SiF4) and water (H2O). (c) Sulfur dioxide reacts with water to form sulfurous acid.

Identify the chemical elements

We can identify the chemical elements involved: Sulfur, Oxygen, and Hydrogen.

Write the chemical formula

Following the rules of chemical nomenclature for molecular compounds, we have: Sulfur dioxide (SO2) reacts with water (H2O) to form sulfurous acid (H2SO3). (d) The substance phosphorus trihydride, commonly called phosphine, is a toxic gas.

Identify the chemical elements

We can identify the chemical elements involved: Phosphorus and Hydrogen.

Write the chemical formula

Following the rules of chemical nomenclature for molecular compounds, we have: The substance phosphorus trihydride, commonly called phosphine (PH3), is a toxic gas. (e) Perchloric acid reacts with cadmium to form cadmium(II) perchlorate.

Identify the chemical elements

We can identify the chemical elements involved: Hydrogen, Oxygen, Chlorine, and Cadmium.

Write the chemical formula

Following the rules of chemical nomenclature for ionic compounds, we have: Perchloric acid (HClO4) reacts with cadmium (Cd) to form cadmium(II) perchlorate (Cd(ClO4)2). (f) Vanadium(II) bromide is a colored solid.

Identify the chemical elements

We can identify the chemical elements involved: Vanadium and Bromine.

Write the chemical formula

Following the rules of chemical nomenclature for ionic compounds, we have: Vanadium(II) bromide (VBr2) is a colored solid.

Key concepts

Chemical Nomenclature

Chemical nomenclature is a set of rules used to name chemical substances. These rules ensure clarity and consistency across scientific communication. Understanding these guidelines is crucial when writing chemical formulas or deciphering them.
For ionic compounds, nomenclature usually involves naming the cation first, followed by the anion. An example is zinc carbonate (ZnCO$_3$), where zinc acts as the cation and carbonate is the anion. Another example is cadmium(II) perchlorate (Cd(ClO$_4$)$_2$). Here, the Roman numeral indicates the charge on the cadmium ion.
In contrast, molecular compounds use prefixes like mono-, di-, tri-, etc., to denote the number of atoms present. For instance, silicon tetrafluoride (SiF$_4$) follows these rules by using 'tetra' to indicate four fluorine atoms bonded to silicon.
Overall, having a good grasp of chemical nomenclature enables easy translation of a compound's name to its chemical formula.

Ionic Compounds

Ionic compounds are formed when positive and negative ions bond together. This bond forms due to the electrostatic attraction between oppositely charged ions.
Typically, ionic compounds consist of metals and non-metals. Take vanadium(II) bromide (VBr$_2$), for example. Vanadium, as a metal, donates electrons and becomes a positively charged ion. Bromine, a non-metal, accepts electrons to become negatively charged.
A crucial aspect of ionic compound nomenclature is balancing the total positive and negative charges. This balance ensures neutrality in the compound, like in cadmium(II) perchlorate where cadmium's +2 charge is balanced by two perchlorate ions, each having a charge of -1.
Overall, understanding ionic compounds involves recognizing these charge interactions and compositional balance, which is key to writing correct chemical formulas.

Molecular Compounds

Molecular compounds, also known as covalent compounds, involve the sharing of electrons between non-metal atoms. These compounds are characterized by the covalent bonds that form between the participating atoms.
One main feature of molecular compounds is that they are often composed of two or more non-metals. For instance, sulphur dioxide (SO$_2$) and phosphine (PH$_3$) are examples where the involved atoms share electrons to achieve stability.
In naming these compounds, prefixes such as mono-, di-, and tri- are essential to indicate the number of each type of atom. Sulphur dioxide (SO$_2$) uses 'di-' to show the presence of two oxygen atoms. Meanwhile, silicon tetrafluoride (SiF$_4$) uses 'tetra-' for four fluorine atoms.
Understanding and identifying molecular compounds helps students accurately convert word descriptions into correct formulas through the use of nomenclature rules.