Question

Give an example of each of the following: (a) a monatomic cation, (b) a monatomic anion, (c) a polyatomic cation, (d) a polyatomic anion.

Short answer

(a) Na^+, (b) Cl^-, (c) NH_4^+, (d) SO_4^{2-}

Step-by-step solution

Understanding Monatomic and Polyatomic Ions

Monatomic ions consist of a single atom with a positive or negative charge due to the loss or gain of electrons. Polyatomic ions, on the other hand, are composed of two or more atoms covalently bonded that carry a charge.

Finding a Monatomic Cation Example

A monatomic cation is a single atom with a positive charge after losing electrons. A common example is the sodium ion, Na^+. Sodium loses one electron to form this cation.

Finding a Monatomic Anion Example

A monatomic anion is a single atom with a negative charge after gaining electrons. A common example is the chloride ion, Cl^-. Chlorine gains one electron to form this anion.

Finding a Polyatomic Cation Example

A polyatomic cation consists of two or more atoms that collectively have a positive charge. An example is the ammonium ion, NH_4^+. The nitrogen and hydrogen atoms are covalently bonded, with the whole group carrying a positive charge.

Finding a Polyatomic Anion Example

A polyatomic anion consists of two or more atoms that collectively have a negative charge. An example is the sulfate ion, SO_4^{2-}. The sulfur and oxygen atoms are covalently bonded, with the whole group carrying a negative charge.

Key concepts

Monatomic Ions

Monatomic ions are ions consisting of a single atom that has either lost or gained electrons, resulting in a net positive or negative charge. These charges occur because atoms strive to reach a stable electron configuration, often similar to the nearest noble gas with a full outer electron shell. For example:

• Sodium ion \(\text{Na}^+\): Sodium loses one electron to achieve the stable electron configuration of neon, leading to a single positively charged ion (cation).


• Chloride ion \(\text{Cl}^-\): Chlorine gains one electron to fill its outer shell, leading to a negatively charged ion (anion).

Monatomic ions play a crucial role in forming ionic compounds, like sodium chloride (table salt), where positive and negative charges attract to hold the compound together. Understanding monatomic ions helps in comprehending how atoms interact and bond with each other in various chemical reactions.

Polyatomic Ions

Polyatomic ions are a group of atoms bonded covalently that carry a net charge, positive or negative. Unlike monatomic ions, these ions consist of more than one atom. They are important in many chemical reactions and biological functions. Some typical examples include:

• Ammonium ion \(\text{NH}_4^+\): Contains nitrogen and hydrogen atoms, bonded together and collectively carrying a positive charge.


• Sulfate ion \(\text{SO}_4^{2-}\): Consists of sulfur and oxygen atoms, bonded together with an overall negative charge.

Polyatomic ions often act as discrete units, undergoing reactions without breaking apart the covalent bonds, which makes them essential components in chemistry. They are commonly found in salts and inorganic compounds. Mastery of polyatomic ions is key to understanding complex structures and the behavior of substances in different environments.

Cations

Cations are positively charged ions formed when atoms lose electrons. The loss of electrons makes the atom less negative and more positive. Cations are typically formed by metals and are essential in various fields such as material science, biology, and medicine. Examples include:

• Sodium ion \(\text{Na}^+\): Formed when sodium loses one electron.


• Ammonium ion \(\text{NH}_4^+\): Technically a polyatomic cation, but illustrates how non-metal groups can also carry a positive charge.

Cations are central to many physical and chemical processes. For instance, they help conduct electricity in solutions, enabling various biochemical processes critical to life. Because they are positively charged, cations attract anions in ionic bonds, facilitating the formation of stable ionic compounds.

Anions

Anions are negatively charged ions formed when atoms or groups of atoms gain electrons. Gaining electrons adds negative charge to the atom or group. These ions generally form from non-metals, and are crucial components in many industrial and biological systems. Examples of common anions include:

• Chloride ion \(\text{Cl}^-\): Formed when chlorine gains one electron.


• Sulfate ion \(\text{SO}_4^{2-}\): A polyatomic anion with sulfur and oxygen atoms carrying a -2 charge.

Anions are key players in forming ionic compounds, reacting with cations to balance out the charge in a compound. Understanding how anions work is essential for grasping basic chemistry concepts and how materials and solutions behave in environments like our bodies or the atmosphere.