Problem 37 - Introductory Chemistry Atoms First

Question

Draw dot diagrams for the following simple ions: (a) \(\mathrm{I}^{-}\) (b) \(\mathrm{O}^{2}\) (c) \(\mathrm{Cl}\) (d) \(\mathrm{H}^{+}\)

Step-by-Step Solution

Answer

\( \mathrm{I}^{-} \): : : I : \( \mathrm{O}^{2-} \): : : O : \( \mathrm{Cl}^{-} \): : : Cl : \( \mathrm{H}^{+} \): H

Step 1: (a) Drawing dot diagram for I⁻

First, we should determine the number of valence electrons iodine (I) has. Iodine is in Group 17 in the Periodic Table, so it has 7 valence electrons. Since it gains one electron to form I⁻ ion, it now has 8 valence electrons. The dot diagram will show the I symbol surrounded by 8 electrons: I⁻: : : I :

Step 2: (b) Drawing dot diagram for O²⁻

Oxygen (O) is in Group 16 in the Periodic Table, so it has 6 valence electrons. When it gains two electrons to form O²⁻ ion, it will have 8 valence electrons. The dot diagram will show the O symbol surrounded by 8 electrons: O²⁻: : : O :

Step 3: (c) Drawing dot diagram for Cl⁻

Chlorine (Cl) is in Group 17 in the Periodic Table, so it has 7 valence electrons. Since it gains one electron to form Cl⁻ ion, it will now have 8 valence electrons. The dot diagram will show the Cl symbol surrounded by 8 electrons: Cl⁻: : : Cl :

Step 4: (d) Drawing dot diagram for H⁺

Hydrogen (H) has only 1 electron in its outermost shell. When it loses one electron to form H⁺ ion, it will have no valence electron left. The dot diagram will show the H symbol with no surrounding electrons: H⁺: H

Key Concepts

Valence Electrons

Valence electrons are the electrons that reside in the outermost shell of an atom and are crucial in determining how the atom will react chemically with other atoms. Elements in the same group (column) on the Periodic Table have the same number of valence electrons and tend to exhibit similar chemical behaviors.

For example, elements in Group 1 have one valence electron, while those in Group 17 have seven valence electrons. These valence electrons are either shared, lost, or gained during chemical reactions to form more stable configurations, often resembling the closest noble gas configuration with eight valence electrons, in what is known as the octet rule. In the exercise given, iodine (I), oxygen (O), and chlorine (Cl) work towards achieving this stable formation, thereby forming ions with complete octet arrangements.

Electron Dot Structure

The electron dot structure, also known as the Lewis dot diagram, is a visual representation that shows the valence electrons of an atom as dots around the element's symbol. These diagrams are instrumental for predicting the bonding behavior of the elements and the structure of molecules they form.

In these diagrams, one dot is equivalent to one valence electron, and the dots are placed around the elements' symbols in a way to represent the real distribution of the electrons as closely as possible. It's a way to visualize how atoms will interact with each other: whether they will likely share electrons to form covalent bonds, or transfer electrons to form ionic bonds. The completion of an octet signifies a chemically stable configuration, as seen in the exercise solutions for the ions I⁻, O²⁻, and Cl⁻, whereas H⁺ loses its only electron, leaving it with none.

Chemical Ions

Chemical ions are atoms or molecules that have gained or lost electrons, resulting in a net charge. An atom becomes a negatively charged ion, known as an anion, by gaining electrons, and a positively charged ion, known as a cation, by losing electrons. This charge imbalance gives ions the ability to interact with other charged particles and participate in the formation of ionic compounds.

• Anions like iodide (I⁻), oxide (O²⁻), and chloride (Cl⁻) have gained one or two electrons to reach the stable octet configuration.
• Cations such as the hydrogen ion (H⁺) have lost electrons, leading in this case to an empty shell.
• The dot diagrams in the exercise show the final electron configurations of these ions after they have undergone electron transfer.

The creation of ions is a fundamental process in chemistry and is essential to many natural phenomena, from the conduction of electricity in electrolytes to the structure of minerals and the biochemistry within our own bodies.