Question

Describe the formation of positive and negative ions. (Chapter 7)

Short answer

In summary, positive ions (cations) form when atoms with low electronegativity, such as metals, lose electrons from their outer shell, creating an imbalance of electric charge within the atom. Negative ions (anions) form when atoms with high electronegativity, such as non-metals, gain electrons into their outer shell, also creating an electric charge imbalance. Ionic bonding, which involves the transfer of electrons between metal and non-metal atoms, plays a crucial role in the formation of positive and negative ions and the resulting compounds. Examples of common cations include Na\(^+\), Ca\(^{2+}\), and Al\(^{3+}\), while examples of common anions include Cl\(^-\), O\(^{2-}\), and S\(^{2-}\).

Step-by-step solution

Understanding Ions and Their Formation

Ions are atoms or molecules that carry a net electric charge due to the loss or gain of electrons. When atoms lose electrons, they become positively charged ions (called cations). When atoms gain electrons, they become negatively charged ions (called anions). The process of forming ions involves the transfer of electrons between atoms, which ultimately leads to the creation of ions.

Formation of Positive Ions (Cations)

Positive ions, or cations, form when an atom loses one or more electrons from its outer shell. This usually occurs in elements with low electronegativity, such as metals. The loss of electrons results in an imbalance of electric charge within the atom, creating a positive charge. Examples of common cations include: 1. Sodium ion (Na\(^+\)) - formed when a sodium atom loses one electron. 2. Calcium ion (Ca\(^{2+}\)) - formed when a calcium atom loses two electrons. 3. Aluminum ion (Al\(^{3+}\)) - formed when an aluminum atom loses three electrons.

Formation of Negative Ions (Anions)

Negative ions, or anions, form when an atom gains one or more electrons into its outer shell. This usually occurs in elements with high electronegativity, such as non-metals. The gain of electrons results in an imbalance of electric charge within the atom, creating a negative charge. Examples of common anions include: 1. Chloride ion (Cl\(^-\)) - formed when a chlorine atom gains one electron. 2. Oxide ion (O\(^{2-}\)) - formed when an oxygen atom gains two electrons. 3. Sulfide ion (S\(^{2-}\)) - formed when a sulfur atom gains two electrons.

Role of Ionic Bonding in Ion Formation

Ionic bonding plays a crucial role in the formation of positive and negative ions. In an ionic bond, a metal atom (cation) donates one or more electrons to a non-metal atom (anion), resulting in the formation of ions with opposite charges. The electrostatic force of attraction between the positively charged metal ion and the negatively charged non-metal ion forms the ionic bond. For example, in the formation of sodium chloride (NaCl), a sodium atom (Na) donates one electron to a chlorine atom (Cl), forming positive sodium ion (Na\(^+\)) and negative chloride ion (Cl\(^-\)). The electrostatic attraction between these two ions forms the ionic bond in sodium chloride. In summary, the formation of positive and negative ions involves the transfer of electrons between atoms, leading to the creation of ions with either a positive or negative charge. Positive ions (cations) form when atoms lose electrons, whereas negative ions (anions) form when atoms gain electrons. Ionic bonding is the key driver in the formation of ions and the resulting compounds.

Key concepts

Cations

Cations are formed when atoms lose electrons, which results in a positive charge. This happens because there are more protons than electrons in the atom after losing electrons. Metals are typically the types of elements that form cations due to their low electronegativity, meaning they do not hold onto electrons very tightly.
For example:

• A sodium atom becomes a sodium ion (Na\(^+\)) when it loses one electron.
• Calcium can form a calcium ion (Ca\(^{2+}\)) by losing two electrons.
• Aluminum becomes an aluminum ion (Al\(^{3+}\)) upon shedding three electrons.

The loss of electrons is a key characteristic of cations, enabling these atoms to achieve a stable electron configuration similar to the nearest noble gas.

Anions

Anions form when an atom gains extra electrons, resulting in a negative charge. This occurs because there are more electrons than protons after the atom gains electrons. Non-metals generally form anions as they have high electronegativity and tend to attract electrons.
Here are some examples:

• A chlorine atom becomes a chloride ion (Cl\(^-\)) after gaining one electron.
• Oxygen forms an oxide ion (O\(^{2-}\)) upon gaining two electrons.
• Sulfur becomes a sulfide ion (S\(^{2-}\)) with the addition of two electrons.

Anions are crucial because they play a significant role in creating stable ionic compounds when they interact with cations.

Ionic Bonding

Ionic bonding is the attractive force that holds cations and anions together in a compound. This bond is formed due to the attraction between ions with opposite charges. When a metal atom gives up its electrons to a non-metal atom, it results in the formation of an ionic compound.
Take, for instance:

• A sodium atom transfers its electron to a chlorine atom forming sodium chloride. This transfer creates a sodium cation (Na\(^+\)) and a chloride anion (Cl\(^-\)).
• The force of attraction between these opposite charges holds the ions together, forming the ionic lattice in sodium chloride.

Ionic bonding is essential in chemical reactions that involve the formation of stable, electrically neutral compounds.

Electron Transfer

Electron transfer is the fundamental process underlying the formation of ions. When atoms exchange electrons, they become ions with either a positive or negative charge. This process leads to the establishment of an ionic bond between participating atoms.
Here’s how it works:

• An atom that loses electrons becomes a cation.
• An atom that gains electrons becomes an anion.
• The flow of electrons from a metal (losing electrons) to a non-metal (gaining electrons) is what creates ionic compounds.

Electron transfer is crucial because it results in a new arrangement of electrons, often making the resulting ions more stable by achieving a full valence electron shell similar to noble gases.