Question

Assign oxidation numbers to each atom in each substance. a) \(\mathrm{CO}\) b) \(\mathrm{CO}_{2}\) c) \(\mathrm{NiCl}_{2}\) d) \(\mathrm{NiCl}_{3}\)

Short answer

a) C: +2, O: -2; b) C: +4, O: -2; c) Ni: +2, Cl: -1; d) Ni: +3, Cl: -1.

Step-by-step solution

Understand the General Rules for Assigning Oxidation Numbers

To assign oxidation numbers, recall: 1. The oxidation number of an element in its natural state is 0. 2. The oxidation number for a monoatomic ion is equal to its charge. 3. Oxygen usually has an oxidation number of -2, and hydrogen is usually +1. 4. The sum of oxidation numbers in a compound or ion must equal the overall charge.

Assign Oxidation Numbers for CO

In carbon monoxide, \(\mathrm{CO}\), carbon and oxygen are bonded. Oxygen usually has an oxidation number of -2. Since the sum must equal 0 (as the compound is neutral), carbon's oxidation number must be +2 to balance out the -2 from oxygen. So,- \(\mathrm{C}: +2\) - \(\mathrm{O}: -2\)

Assign Oxidation Numbers for CO2

In carbon dioxide, \(\mathrm{CO}_2\), oxygen's oxidation number is typically -2. With two oxygens, the total is -4. To balance this and maintain the neutral charge of the molecule, carbon has an oxidation number of +4. Therefore,- \(\mathrm{C}: +4\) - \(\mathrm{O}: -2\) (each)

Assign Oxidation Numbers for NiCl2

In \(\mathrm{NiCl}_2\), chlorine usually has an oxidation number of -1. With two chlorines, the total negative charge is -2. Ni must balance this with +2 to ensure the compound's charge is 0. Thus, - \(\mathrm{Ni}: +2\) - \(\mathrm{Cl}: -1\) (each)

Assign Oxidation Numbers for NiCl3

In \(\mathrm{NiCl}_3\), each chlorine is -1, giving a total of -3 for the Cl ions. Hence, Ni must be +3 to balance the compound's charge to zero. Therefore,- \(\mathrm{Ni}: +3\) - \(\mathrm{Cl}: -1\) (each)

Key concepts

Chemical Compounds

Chemical compounds are substances composed of two or more different elements that are chemically bonded together. These compounds can have distinct formulas and properties. Understanding their composition helps in determining how they interact in chemical reactions.
For instance, in the compound carbon monoxide (\(\mathrm{CO}\)), carbon and oxygen are combined in a fixed ratio to form a stable chemical compound. These elements bond together through chemical forces that involve sharing or transfer of electrons. Similarly, compounds like \(\mathrm{CO}_2\), \(\mathrm{NiCl}_2\), and \(\mathrm{NiCl}_3\) are also formed by specific combinations of atoms.

• \(\mathrm{CO}\): Consists of one carbon atom and one oxygen atom.
• \(\mathrm{CO}_2\): Made up of one carbon atom and two oxygen atoms.
• \(\mathrm{NiCl}_2\): Contains one nickel atom and two chlorine atoms.
• \(\mathrm{NiCl}_3\): Has one nickel atom and three chlorine atoms.

Grasping the structure of these compounds is crucial because it lays the groundwork for understanding how compounds will behave in different reactions.

Oxidation State

The oxidation state, or oxidation number, is an essential concept in chemistry. It reflects the degree of oxidation of an atom in a compound, indicating how electrons are shared among atoms. In simple terms, it helps determine an atom's charge in a compound if all bonds were ionic.
For example, in \(\mathrm{CO}\), the oxidation state of oxygen is -2, and carbon is +2. This configuration shows how electrons are distributed within the molecule, with oxygen being more electronegative and pulling electrons towards itself. Similarly, in \(\mathrm{CO}_2\), carbon shows an oxidation state of +4 due to two oxygen atoms each taking two electrons (a total of four electrons taken).

• Assigning oxidation states helps chemists understand electron flow in reactions.
• It is also vital for identifying redox reactions, where oxidation and reduction processes occur simultaneously.
• This further assists in balancing chemical equations.

Knowing oxidation states helps chemists predict how substances will react with each other.

Charge Balance

Charge balance is a principle in chemistry stating that the total charges in a compound must sum to zero, maintaining a net neutral charge. This principle ensures that matter adheres to the conservation laws, maintaining a balance of positive and negative charges.
In compounds like \(\mathrm{NiCl}_2\), each chlorine atom holds a charge of -1. The nickel must, therefore, balance this with a +2 charge since two chlorine atoms contribute a total negative charge of -2. Likewise, in \(\mathrm{NiCl}_3\), with three chloride ions each at -1, nickel attains a +3 charge to offset the total -3 charge from chlorine.

• Charge balance is critical for the stability of compounds.
• It is crucial for calculating correct formulas for ionic compounds.
• Charge balance aids in ensuring that chemical reactions are balanced.

When working with chemical reactions, remembering charge balance helps prevent errors and ensures correct stoichiometry.

Elementary Rules in Chemistry

Chemistry involves a set of elementary rules that guide how elements interact and form compounds. These rules help in fundamental analyses such as determining oxidation states and charge balances.
1. The oxidation number of a free element, one not combined with different elements, is zero.
2. For monoatomic ions, the oxidation number is equal to the ion's charge, such as \(\mathrm{Cl}^-\) having an oxidation number of -1.
3. Oxygen typically has an oxidation state of -2, except in peroxides or when bonded to fluorine.
4. The sum of the oxidation numbers in a neutral compound must be zero, or it must equal the charge of the ion for polyatomic ions.

• These rules help predict product formation and reaction pathways.
• They serve as a foundation for more advanced chemical concepts.
• Understanding these rules is crucial for solving complex chemical problems.

By adhering to these basic rules, chemists can systematically determine important properties and behaviors of chemical substances.