Question

Use Lewis structures to show that the hydronium ion, \(\mathrm{H}_{3} \mathrm{O}^{+},\) can be considered to be formed by the creation of a coordinate covalent bond between \(\mathrm{H}_{2} \mathrm{O}\) and \(\mathrm{H}^{+} .\)

Short answer

The hydronium ion \(\mathrm{H}_3\mathrm{O}^+\) is formed by the water molecule \(\mathrm{H}_2\mathrm{O}\) donating one of its lone pairs to bond with a \(\mathrm{H}^+\) ion, creating a coordinate covalent bond and resulting in a structure with three covalent bonds and one lone pair on the oxygen, along with a positive charge.

Step-by-step solution

Draw the Lewis structure of water (H2O)

Begin by drawing the Lewis structure for a water molecule. Oxygen has 6 valence electrons and each hydrogen has 1 valence electron. Arrange the electrons to form two covalent bonds between Oxygen and each Hydrogen. The remaining 4 electrons on Oxygen will be in two lone pairs.

Represent the hydrogen ion (H+)

Illustrate the hydrogen ion simply as \(\mathrm{H}^+\) with no valence electrons, because it has given up its single electron and carries a positive charge.

Formation of the coordinate covalent bond

To form the hydronium ion, one of the lone pairs on the oxygen in \(\mathrm{H}_2\mathrm{O}\) donates an electron pair to the hydrogen ion \(\mathrm{H}^+\), forming a coordinate covalent bond. Now oxygen in the resulting hydronium ion will have three bonds and one lone pair.

Complete the Lewis structure of hydronium ion (H3O+)

Finalize the Lewis structure by showing the oxygen with one lone pair and now having three bonds with hydrogen atoms. It's important to denote the positive charge on the structure, which is due to the oxygen donating one of its electron pairs to bond with an additional hydrogen ion.

Key concepts

Hydronium Ion

The hydronium ion is a fascinating species in chemistry, often symbolized as \(\mathrm{H}_3\mathrm{O}^+\). It's essentially a water molecule, \(\mathrm{H}_2\mathrm{O}\), that has an extra hydrogen nucleus (\(\mathrm{H}^+\)) associated with it via a special kind of bond which we'll discuss shortly. This positively charged ion plays a crucial role in acid-base chemistry, acting as a proton donor in many reactions.

When water accepts a proton \(\mathrm{H}^+\), it forms the hydronium ion, leading to its positive charge. In solution, these ions are very active and are an essential part of understanding pH and the acidity of substances. The Lewis structure of the hydronium ion shows this interaction clearly and is a foundational concept in understanding how acids behave in water.

Coordinate Covalent Bond

Let's dive into the coordinate covalent bond, sometimes also called a dative bond. In a regular covalent bond, each atom typically contributes one electron to form a shared pair. However, in a coordinate covalent bond, both electrons in the shared pair come from the same atom.

This type of bonding is beautifully demonstrated when a hydronium ion is formed. Oxygen, holding a pair of unshared electrons, reaches out and forms a bond with a hydrogen ion (which lacks electrons) by offering its own lone pair. This generous act creates the coordinate covalent bond, which is just as strong and stable as any other covalent bond but has this unique 'one-sided' electron donation characteristic.

Valence Electrons

Valence electrons are the electrons in the outermost shell of an atom, and they play the starring role in chemical bonding. In molecules, the valence electrons are the ones that get involved in forming bonds or exist as lone pairs of electrons on atoms.

In the context of the hydronium ion, oxygen begins with six valence electrons and hydrogen has one each. By keeping track of these electrons, we can understand how bonds form and why certain structures, like the hydronium ion, have the shape and charge they do. Lewis structures, which highlight these valence electrons, help us visualize where the electrons are and which atoms they are associated with - a critical step in predicting the reactivity and properties of molecules.

Chemical Bonding

Chemical bonding is the force that holds atoms together in molecules and compounds. There's a variety of bond types, with covalent and ionic bonds being the most common.

In covalent bonding, atoms share electrons to achieve a full outer shell, leading to stability. Ionic bonds, on the other hand, result from the complete transfer of electrons from one atom to another, creating oppositely charged ions.

The hydronium ion creation involves both covalent and coordinate covalent bonding. The water molecule forms with regular covalent bonds, while the attachment of the extra hydrogen ion is through a coordinate covalent bond. Through understanding chemical bonding, students gain insight into the structure and behavior of molecules, which is fundamental for mastering chemistry.