Question

Represent the following ionic compounds by Lewis structures: (a) barium hydroxide; (b) sodium nitrite; (c) magnesium iodate; (d) aluminum sulfate.

Short answer

Lewis structures for ionic compounds represent the transfer of electrons from one atom to the other resulting in ions. In the case of the four compounds listed, the metal atoms each lose electrons to become positive cations, while the nonmetal groups each gain electrons to become negative anions. Draw the structures with the metal atoms having no electrons and the nonmetal groups surrounded by 8 electrons.

Step-by-step solution

Drawing Lewis Structure for Barium Hydroxide

To start, remember Barium has 2 valence electrons and Hydroxide has 7. In the structure, Barium must lose 2 electrons (forming a 2+ cation) and each Hydroxide must gain one electron (forming a 1- anion). Draw Barium with no electrons around it and two Hydroxides each surrounded by 8 electrons.

Drawing Lewis Structure for Sodium Nitrite

Sodium has 1 valence electron and Nitrite (NO2) has 5 electrons from Nitrogen and 6 from each Oxygen. In the structure, Sodium must lose 1 electron (forming a 1+ cation) and Nitrite must gain one electron (forming a 1- anion). Draw Sodium with no electrons around it and Nitrite surrounded by 8 electrons in each atom.

Drawing Lewis Structure for Magnesium Iodate

Magnesium has 2 valence electrons and Iodate (IO3) has 7 electrons from Iodine and 6 from each Oxygen. In the structure, Magnesium must lose 2 electrons (forming a 2+ cation) and each Iodate must gain one electron (forming a 1- anion). Draw Magnesium with no electrons around it and three Iodates each surrounded by 8 electrons.

Drawing Lewis Structure for Aluminum Sulfate

Aluminum has 3 valence electrons and Sulfate (SO4) has 6 electrons from Sulfur and 6 from each Oxygen. In the structure, each Aluminum must lose 3 electrons (forming a 3+ cation) and each Sulfate must gain two electrons (forming a 2- anion). Draw two Aluminums each with no electrons around them and three Sulfates each surrounded by 8 electrons.

Key concepts

Ionic Compounds

Ionic compounds are formed when atoms transfer electrons to achieve stable electron configurations. This process typically happens between metals and non-metals. Metals lose electrons to become positively charged cations, while non-metals gain those electrons, becoming negatively charged anions. This transfer of electrons forms the basis of ionic bonds, which are the electrostatic attractions between oppositely charged ions.
In the exercise, we look at different ionic compounds, each comprising cations and anions. For example, barium hydroxide involves barium (a metal) losing electrons, while the hydroxide ion (a non-metal part) gains them. These interactions lead to the formation of a stable ionic compound.
Understanding ionic compounds is fundamental in grasping more complex chemical interactions. Ionic compounds often form crystal lattice structures that make them strong and have high melting and boiling points. They also conduct electricity when molten or dissolved in water.

Valence Electrons

Valence electrons are the outermost electrons of an atom and determine the atom's chemical reactivity and bonding behavior. Valence electrons are crucial because they participate in the formation of chemical bonds.
In ionic bonding, atoms will either lose or gain valence electrons to reach a full outer shell, often achieving a stable electron configuration similar to noble gases. For example, in sodium nitrite, sodium has one valence electron, which it donates to the nitrite ion. After transferring its electron, sodium attains a stable configuration.
Determining the number of valence electrons in an atom allows us to predict how it will interact with other atoms, which is essential when drawing Lewis structures. In a Lewis structure, valence electrons are represented as dots around the element symbol. These diagrams help visualize the number of electrons shared or transferred between atoms in a compound.

Cation and Anion Formation

The formation of cations and anions is a crucial step in the creation of ionic compounds. Cations are formed when atoms lose electrons, resulting in a positive charge. For example, in magnesium iodate, magnesium loses two electrons to form a Mg^{2+} cation.
Anions, on the other hand, are formed when atoms gain electrons, resulting in a negative charge. In the exercise, when magnesium donates electrons, the iodate ion gains them, forming an anion with a negative charge. This transfer of electrons is essential for the formation of stable ionic bonds, where the positive cations and negative anions attract each other.
Recognizing how cations and anions form is a significant part of understanding chemical reactions, especially in the context of ionic compounds. This knowledge is fundamental for drawing accurate Lewis structures and predicting how elements will combine.

Chemical Bonding Representations

Chemical bonds are often represented using Lewis structures, which provide a simple visual of how atoms bond in a molecule. Lewis structures involve using element symbols surrounded by dots representing valence electrons. These structures are an effective way to illustrate the transfer of electrons in ionic bonds.
For aluminum sulfate in the exercise, the aluminum atom loses electrons to form a cation, depicted with no surrounding dots, while sulfate, which gains electrons, is shown with complete electron pairs around it. The symbols and dots depict how electron pairs or shared electrons contribute to the stability of compounds.
Understanding chemical bonding representations like Lewis structures helps students visualize complex chemical interactions. These representations serve as a foundation not just in ionic bonding but also in other types of chemical bonding, providing valuable insights into the behavior of elements and their interactions with each other.