Question

In the ionic compounds the oxidation number of an ion (1) is the same as the charge of the ion. (2) is the same as the charge of the ion with opposite sign (3) is always zero (4) cannot be inferred from the formulae of the compounds

Short answer

Option (1) is correct.

Step-by-step solution

Identify the Meaning of Oxidation Number

The oxidation number of an element in a compound is indicative of its degree of oxidation (loss of electrons) or reduction (gain of electrons). It is a theoretical charge an atom would have if all bonds were ionic.

Relation Between Oxidation Number and Ion Charge

For ionic compounds, the oxidation number of any ion is typically the same as its charge. For example, in NaCl, the Na+ ion has an oxidation number of +1 and the Cl- ion has an oxidation number of -1.

Analyze Each Option

Option (1) suggests the oxidation number is the same as the charge of the ion. This is true for ionic compounds. Option (2) is incorrect because the oxidation number is not opposite in sign. Option (3) is incorrect because the oxidation number is not always zero. Option (4) is incorrect because the oxidation number can be inferred from the formula of ionic compounds.

Conclusion

Based on the analysis, the correct option is (1) since the oxidation number of an ion in ionic compounds is the same as the charge of the ion.

Key concepts

Ionic Compounds

Ionic compounds are chemical compounds comprised of ions bonded together by electrostatic forces, commonly known as ionic bonds. These compounds are typically formed between metals and non-metals. For example, sodium chloride (NaCl) is an ionic compound. In sodium chloride, sodium (a metal) loses one electron to become a positively charged ion (Na+), while chloride (a non-metal) gains that electron to become a negatively charged ion (Cl-). This transfer of electrons creates ions which are then held together by the strong electrostatic attraction between them. This bond is the essence of ionic compounds. It's important to remember that ionic compounds usually have high melting and boiling points due to the strong attraction between ions. Also, they are often soluble in water and can conduct electricity when dissolved because the ions are free to move.

Ion Charge

The ion charge refers to the electric charge that an ion carries, which results from the loss or gain of electrons. In ionic compounds, each element has its typical ion charge. Metals, which are typically found on the left side of the periodic table, tend to lose electrons and form positively charged ions known as cations. For example, sodium (Na) loses one electron to become Na+.
On the other hand, non-metals, which are found on the right side of the periodic table, tend to gain electrons, forming negatively charged ions known as anions. For instance, chlorine (Cl) gains one electron to become Cl-. Understanding ion charges is crucial because it helps determine the formula of the ionic compound. For instance, in NaCl, knowing that sodium creates Na+ and chlorine forms Cl- allows us to understand the 1:1 ratio of ions needed to form the neutral compound sodium chloride.

Oxidation and Reduction

Oxidation and reduction, often referred to as redox reactions, are chemical reactions where electrons are transferred between substances. In oxidation, an element loses electrons, thereby increasing its oxidation state. For example, when sodium (Na) becomes Na+, it loses one electron, which is an oxidation process. Conversely, reduction involves an element gaining electrons, decreasing its oxidation state. For instance, when chlorine (Cl) becomes Cl-, it gains an electron, which is a reduction process. These redox processes are essential for many chemical reactions, including those in ionic compounds. Understanding redox reactions also helps in determining oxidation numbers, which are hypothetical charges an atom would have if the compound was composed of ions. In an ionic compound, the oxidation number corresponds directly to the ion's charge. For example, in NaCl, Na+ has an oxidation number of +1 while Cl- has an oxidation number of -1.