Problem 63 - Chemistry: The Central Science in SI Units, Global Edition

Question

Give the chemical formula for (a) copper(II) carbonate, (b) carbon monoxide, (c) magnesium hydrogen carbonate, (d) lithium acetylide, (e) carbon tetrafluoride.

Step-by-Step Solution

Answer

(a) CuCO₃, (b) CO, (c) Mg(HCO₃)₂, (d) Li₂C₂, (e) CF₄

Step 1: (a) Copper(II) carbonate

Copper(II) means that the copper ion has a +2 charge. Carbonate is a polyatomic ion with the formula CO₃²⁻. To form a neutral compound, we need one copper(II) ion to pair with one carbonate ion. So the chemical formula for copper(II) carbonate is CuCO₃.

Step 2: (b) Carbon monoxide

Carbon monoxide is a covalent compound composed of one carbon atom and one oxygen atom. The prefix "mono-" means one, indicating that there is one oxygen atom. So, the chemical formula for carbon monoxide is CO.

Step 3: (c) Magnesium hydrogen carbonate

Magnesium is in group 2 of the periodic table and forms +2 ions (Mg²⁺). Hydrogen carbonate, also known as bicarbonate, is a polyatomic ion with the formula HCO₃⁻. To form a neutral compound, we need one magnesium ion to pair with two hydrogen carbonate ions. So the chemical formula for magnesium hydrogen carbonate is Mg(HCO₃)₂.

Step 4: (d) Lithium acetylide

Lithium is in group 1 of the periodic table and forms +1 ions (Li⁺). Acetylide is the ion of the compound acetylene (C₂H₂) with two hydrogen atoms removed, leaving the ion C₂²⁻. To form a neutral compound, we need two lithium ions to balance the charge of one acetylide ion. So the chemical formula for lithium acetylide is Li₂C₂.

Step 5: (e) Carbon tetrafluoride

Carbon tetrafluoride is a covalent compound composed of one carbon atom and four fluorine atoms. The prefix "tetra-" means four, indicating that there are four fluorine atoms. So, the chemical formula for carbon tetrafluoride is CF₄.

Key Concepts

Polyatomic Ions

Polyatomic ions are fascinating clusters of atoms that possess a collective charge, either positive or negative. They often act as a single unit in chemical reactions. These ions are entirely based on the number of protons and electrons they contain, where an imbalance between them results in the charge.

• The carbonate ion \(\text{CO}_3^{2-}\) is a common polyatomic ion. It has a 2- charge as it contains more electrons than needed for a neutral charge. This is due to the extra electrons that are not balanced by protons.
• Another example is the hydrogen carbonate \(\text{HCO}_3^{-}\), also known as bicarbonate, which possesses a 1- charge.
• These ions often combine with metal ions to form ionic compounds. For instance, copper(II) carbonate \(\text{CuCO}_3\) and magnesium hydrogen carbonate \(\text{Mg(\text{HCO}_3)_2}\) form when polyatomic ions pair with metal ions of opposite charge.

Understanding polyatomic ions involves recognizing both their formulas and how they combine to create compounds. Learning their names and charges, along with memorizing some common ones, helps in determining chemical formulas quickly and accurately.

Covalent Compounds

Covalent compounds are formed when two or more nonmetal atoms share electrons. This type of bonding usually results in small collections of atoms, known as molecules, which possess unique properties.

• Carbon monoxide \(\text{CO}\) is a common example of a covalent compound. Here, both carbon and oxygen atoms share electrons, satisfying each other's needs for a full outer shell.
• Another covalent compound is carbon tetrafluoride \(\text{CF}_4\), where one carbon atom shares electrons with four fluorine atoms. The prefix 'tetra-' signifies the presence of four fluorine atoms.

Covalent bonds result from the attractive force that exists between the electrons of one atom and the nucleus of another. This electron sharing aspect contributes to the unique properties of covalent compounds, such as their lower melting and boiling points compared to ionic compounds.

Periodic Table

The periodic table is an essential tool in chemistry, organizing all known elements in a visually intuitive way. It helps in understanding patterns and predicting properties of elements based on their positions.

• Group 1, known as the alkali metals, includes elements like lithium, which forms +1 ions (e.g., \(\text{Li}^+\)) in compounds such as lithium acetylide \(\text{Li}_2\text{C}_2\).
• Group 2, known as the alkaline earth metals, includes magnesium, which typically forms +2 ions (e.g., \(\text{Mg}^{2+}\)) as found in magnesium hydrogen carbonate \(\text{Mg(\text{HCO}_3)_2}\).

Each element's position provides insights into its chemical behavior. Learning about group properties and periodic trends, like electronegativity and atomic radius, deepens the understanding of chemical interactions in various compounds.