Question

Write the formulas for the following compounds (refer to your answers to Problem 30 ). a. sodium cyanide b. calcium carbonate c. potassium hydrogen carbonate d. magnesium acetate

Short answer

The formulas for the given compounds are: a. Sodium cyanide: \(NaCN\) b. Calcium carbonate: \(CaCO_3\) c. Potassium hydrogen carbonate: \(KHCO_3\) d. Magnesium acetate: \(Mg(C_2H_3O_2)_2\)

Step-by-step solution

a. Sodium cyanide

Step 1: Determine the ions Sodium (Na) is an alkali metal, which forms a cation with a +1 charge (Na+). Cyanide (CN) is a polyatomic anion with a -1 charge (CN-). Step 2: Write the chemical formula Since the charges of the ions are already balanced (+1 and -1), the chemical formula is simply NaCN. So, the formula for sodium cyanide is NaCN.

b. Calcium carbonate

Step 1: Determine the ions Calcium (Ca) is an alkaline earth metal, which forms a cation with a +2 charge (Ca²⁺). Carbonate (CO₃) is a polyatomic anion with a -2 charge (CO₃²⁻). Step 2: Write the chemical formula Since the charges of the ions are balanced (+2 and -2), the chemical formula is simply CaCO₃. So, the formula for calcium carbonate is CaCO₃.

c. Potassium hydrogen carbonate

Step 1: Determine the ions Potassium (K) is an alkali metal, which forms a cation with a +1 charge (K⁺). Hydrogen carbonate (HCO₃) is a polyatomic anion with a -1 charge (HCO₃⁻). Step 2: Write the chemical formula Since the charges of the ions are balanced (+1 and -1), the chemical formula is simply KHCO₃. So, the formula for potassium hydrogen carbonate is KHCO₃.

d. Magnesium acetate

Step 1: Determine the ions Magnesium (Mg) is an alkaline earth metal, which forms a cation with a +2 charge (Mg²⁺). Acetate (C₂H₃O₂) is a polyatomic anion with a -1 charge (C₂H₃O₂⁻). Step 2: Write the chemical formula Since the Magnesium ion has a +2 charge and the acetate ion has a -1 charge, we need two acetate ions to balance the charge. So, the chemical formula is Mg(C₂H₃O₂)₂. Hence, the formula for magnesium acetate is Mg(C₂H₃O₂)₂.

Key concepts

Ionic Compounds

Ionic compounds are formed when electrons are transferred from one atom to another. This creates two oppositely charged ions: a positive cation and a negative anion. The attraction between these opposite charges holds the compound together. Ionic compounds typically form between metals and non-metals. The metal atoms lose electrons to become positive cations, while non-metal atoms gain electrons to become negative anions. Here are a few important characteristics of ionic compounds:

• They have high melting and boiling points due to strong ionic bonds.
• In solid form, they don't conduct electricity, but in molten state or dissolved in water, they become conductive.
• They usually form crystalline solids with a definite structure.

Recognizing the formation and properties of ionic compounds is crucial for understanding how substances interact at an atomic level.

Polyatomic Ions

Polyatomic ions are ions that consist of more than one atom. These ions behave as a single unit with a specific charge, which can be positive or negative. Polyatomic ions are essential in forming various chemical compounds. A well-known example of a polyatomic ion is the carbonate ion, \(\text{CO}_3^{2-}\). It consists of one carbon atom and three oxygen atoms. Another example is the acetate ion, \(\text{C}_2\text{H}_3\text{O}_2^-\), comprised of two carbon atoms, three hydrogen atoms, and two oxygen atoms.Polyatomic ions often end with suffixes like "-ate" or "-ite," which help identify them:

• "-ate" indicates a higher number of oxygen atoms.
• "-ite" suggests a lower number of oxygen atoms.

Understanding the composition and naming of polyatomic ions aids in writing chemical formulas and recognizing them in reactions.

Chemical Nomenclature

Chemical nomenclature is the system used to name chemical compounds. It helps standardize and make communication about chemicals more precise and universal.For ionic compounds, the name typically consists of the cation name followed by the anion name. The name of simple monoatomic cations is the same as the element, while the anion's name usually ends in "-ide."For compounds with polyatomic ions, the name of the polyatomic ion is used directly. For example:- Sodium cyanide (\(\text{NaCN}\)) is named after the ions sodium (\(\text{Na}^+\)) and cyanide (\(\text{CN}^-\)).- Calcium carbonate (\(\text{CaCO}_3\)) includes calcium (\(\text{Ca}^{2+}\)) and carbonate (\(\text{CO}_3^{2-}\)).Knowing chemical nomenclature is crucial for correctly understanding and writing chemical formulas, ensuring scientists and students worldwide can accurately share information.