Question

Draw a Lewis structure for each of the following ionic compounds: a. \(\mathrm{KI}\) b. \(\mathrm{CaBr}_{2}\) c. \(\mathrm{K}_{2} \mathrm{~S}\) d. \(\mathrm{MgS}\)

Short answer

Lewis structures for the given compounds are as follows: a) KI consists of K+ and I- ions, b) CaBr2 consists of a Ca2+ ion and two Br- ions, c) K2S consists of two K+ ions and one S2- ion, d) MgS consists of an Mg2+ ion and an S2- ion.

Step-by-step solution

Understanding Lewis Structures for Ionic Compounds

Lewis structures for ionic compounds represent the transfer of electrons from the metal atoms to the non-metal atoms. Cations (positive ions) are typically metals that lose electrons, resulting in a full outer shell similar to the nearest noble gas. Anions (negative ions) are typically non-metals that gain electrons, achieving a full outer shell. In these structures, brackets are used to indicate the charged ions with the charge written as superscript outside the bracket.

Drawing Lewis Structure for KI

Potassium (K) has 1 valence electron and iodine (I) has 7 valence electrons. Potassium loses one electron to iodine to achieve a noble gas electron configuration. The K becomes K+ and I becomes I-. The Lewis structure will show the K+ ion and the I- ion with 8 electrons around I, representing the gained electron.

Drawing Lewis Structure for CaBr2

Calcium (Ca) has 2 valence electrons and bromine (Br) has 7 valence electrons. Calcium loses two electrons to two bromine atoms to achieve a noble gas electron configuration. The Ca becomes Ca2+ and each Br atom becomes Br-. The Lewis structure will show the Ca2+ ion and two Br- ions, each with 8 electrons, representing the gained electrons.

Drawing Lewis Structure for K2S

Potassium (K) has 1 valence electron and sulfur (S) has 6 valence electrons. Two potassium atoms each lose one electron to sulfur, resulting in each K becoming K+ and S becoming S2-. The Lewis structure will show two K+ ions and one S2- ion with 8 electrons around the S, representing the gained electrons.

Drawing Lewis Structure for MgS

Magnesium (Mg) has 2 valence electrons and sulfur (S) has 6 valence electrons. Magnesium loses its two electrons to sulfur to achieve a noble gas electron configuration. The Mg becomes Mg2+ and the S becomes S2-. The Lewis structure will show the Mg2+ ion and the S2- ion with 8 electrons around the S, representing the gained electrons.

Key concepts

Electron Transfer in Ionic Bonding

When it comes to understanding ionic compounds, one must first grasp the process of electron transfer in ionic bonding. This is a crucial concept in chemistry. Ionic bonding is the type of chemical bond where an atom, typically a metal, loses one or more electrons to become a positively charged ion, known as a cation. Conversely, a non-metal atom gains those electrons to become a negatively charged ion, known as an anion. The result is a strong electrostatic force of attraction between the oppositely charged ions.

For instance, in a salt like sodium chloride (NaCl), sodium (Na) loses an electron and becomes Na+, while chlorine (Cl) gains an electron to become Cl-. This exchange leads to a full outer shell for each ion, aligning them with the electron configuration of a noble gas, which is a stable structure. The overall process transforms atoms into ions that then stick together due to opposite charges, creating an ionic compound. It is this 'give and take' nature of electron transfer that is the foundation of ionic bonding.

Drawing Lewis Structures

Moving forward to drawing Lewis structures for ionic compounds, visualizing the electron transfer becomes easier. A Lewis structure is a diagrammatic method that depicts the bonds between atoms of a molecule and the lone pairs of electrons that may exist. These structures serve as a guide to understand the bonding as well as the electron arrangement in the creation of molecules or compounds.

In the context of ionic compounds, Lewis structures show the loss and gain of electrons and the resulting charges on ions. To illustrate the bonds in an ionic compound correctly, remember these pointers:

• Identify the valence electrons for each atom.
• Determine how many electrons are transferred between atoms to achieve noble gas electron configuration.
• Draw the resulting ions with their charges and represent the transferred electrons as dots around the non-metal ion.

Brackets are typically used to enclose the ions with the appropriate charge indicated as a superscript. This representation provides clarity about the ionic compound's structure at a glance.

Valence Electrons and Ion Formation

The formation of ions from atoms is a phenomenon intrinsically linked to the valence electrons these atoms possess. Valence electrons can be thought of as the 'currency' of chemical bonding; they are the outermost electrons of an atom and play a pivotal role in the formation of chemical bonds. During ionic bonding, atoms will either lose or gain valence electrons to achieve a stable electron configuration, usually that of the nearest noble gas.

Metals, which tend to form cations, often have one to three valence electrons that they 'prefer' to lose. Non-metals, on the other hand, tend to form anions and typically have five to seven valence electrons, putting them closer to filling their valence shell by gaining electrons rather than losing them. This exchange of valence electrons leads to the creation of ions: atoms or molecules with a net electrical charge. As such, understanding the concept of valence electrons is fundamental when predicting the charge an ion will have and the formula of the resulting ionic compound.