Problem 31 - Chemistry Matter and Change

Question

\(\mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}\)

Step-by-Step Solution

Answer

Copper(II) nitrate, represented by the formula \(\mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}\), is an ionic compound composed of copper(II) cations (\(\mathrm{Cu}^{2+}\)) and nitrate anions (\(\mathrm{NO₃⁻}\)). To form a stable compound, the charges must be balanced, resulting in one copper(II) cation (\(\mathrm{Cu}^{2+}\)) combining with two nitrate anions (\(2\mathrm{NO₃⁻}\)). The final chemical formula for copper(II) nitrate is \(\mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}\).

Step 1: Identify the elements in the formula

Firstly, we need to identify the elements in the compound. In the formula \(\mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}\), there are three elements: copper, nitrogen and oxygen. The symbols for these elements are Cu, N, and O respectively.

Step 2: Understand the charges of the ions

Copper(II) nitrate is an ionic compound, which means it is formed by the chemical bonding of ions. In this case, the ions involved are the copper(II) cation (Cu^{2+}) and the nitrate anion (NO₃⁻). Copper is a transition metal and can form cations with different charges. In this case, we have copper(II), which means it forms a cation with a charge of +2: Cu^{2+}. The nitrate ion, which is a polyatomic ion, consists of one nitrogen atom and three oxygen atoms bonded together, with a total charge of -1: NO₃⁻.

Step 3: Balance the charges

In order to form a stable ionic compound, the charges of the ions must balance out. We have a copper(II) cation with a charge of +2 (Cu^{2+}) and a nitrate anion with a charge of -1 (NO₃⁻). In order to balance the charges, we need two nitrate ions (with a total charge of -2) to pair with one copper(II) cation (with a charge of +2). This results in the following combination: Cu^(2+) + 2(NO₃⁻)

Step 4: Write the final formula

Now, we can write the chemical formula for copper(II) nitrate. Since we need one Cu^(2+) ion and two NO₃⁻ ions, we can represent this as: Cu(NO₃)₂ This is the final formula for copper(II) nitrate: \(\mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}\).

Key Concepts

Ionic Compounds

Ionic compounds are a type of chemical compound that form through the electrostatic attraction between oppositely charged ions. This means that one part of the compound will donate electrons, becoming positively charged (a cation), while the other part will accept electrons, becoming negatively charged (an anion). This exchange of electrons creates a strong bond that holds the compound together.

For example, in the case of copper(II) nitrate, the copper ion

• donates two electrons and becomes a positive copper(II) cation ( Cu ²⁺).

The nitrate ion is the part that accepts electrons, gaining a negative charge. These ions are stacked in a manner that the attractive forces between them make the whole structure stable.

Ionic compounds generally have high melting and boiling points because the ionic bonds require a lot of energy to break. They also dissolve in water to some extent and often conduct electricity when melted or dissolved due to the movement of ions.

Polyatomic Ions

Polyatomic ions are ions consisting of multiple atoms bonded together that act as a single charged entity. They differ from regular ions, which typically consist of only one atom. This combination of atoms often involves covalent bonds, where electrons are shared rather than transferred.

The nitrate ion ( NO ₃ ^-) in copper(II) nitrate is an example of a polyatomic ion.

• This ion is made up of one nitrogen atom covalently bonded to three oxygen atoms.
• Together, they carry an overall negative charge.

Polyatomic ions are key components in many ionic compounds and play a vital role in many chemical reactions. Because they act as a unit, these ions determine much of the chemistry of the compounds they form. Recognizing and understanding polyatomic ions is important for predicting the properties of ionic compounds.

Chemical Bonding

Chemical bonding refers to the forces that hold atoms together in compounds. This includes both ionic and covalent bonds. In the context of copper(II) nitrate, we see both types of bonding at play.

The bond between the copper cation and the nitrate anion is ionic. This occurs via electrostatic forces between the oppositely charged ions.
Within the nitrate ion itself, nitrogen and oxygen atoms share electrons, forming covalent bonds.

• Ionic bonds contribute to the stability and structure of solid compounds.
• Covalent bonds, meanwhile, account for the distinct shape and chemistry of polyatomic ions.

Understanding these bonds is crucial for comprehending the physical and chemical properties of materials. Bonds determine how a substance look and behaves at a microscopic level.

Transition Metals

Transition metals are elements found in the center of the periodic table, specifically in the groups 3 through 12. They are unique due to their ability to form multiple positive ions. Copper, in this case, is a transition metal capable of forming ions with different charges, such as Cu⁺ or Cu²⁺.

This flexibility arises from the electron configuration of transition metals, which allow for variable oxidation states. In copper(II) nitrate, copper is in the +2 oxidation state.

• Transition metals like copper possess properties such as high conductivity and the ability to form alloys with other metals.
• They also often display vibrant colors and are used in many practical applications like catalysts and coins.

Understanding how transition metals bond and interact in compounds is crucial for both chemistry enthusiasts and students. It helps in predicting reactions and designing new materials with specific properties.