Problem 118 - Chemistry The Molecular Science

Question

Draw diagrams of each nanoscale situation given in parts (a)-(c). Represent atoms or monoatomic ions as circles; represent molecules or polyatomic ions by overlapping circles for the atoms that make up the molecule or ion; and distinguish among different kinds of atoms by labeling or shading the circles. In each case draw representations of at least five nanoscale particles. Your diagrams can be two-dimensional. (a) A sample of solid lithium nitrate, \(\mathrm{LiNO}_{3}\) (b) A sample of molten lithium nitrate (c) A molten sample of lithium nitrate after electrodes have been placed into it and a direct current applied to the electrodes

Step-by-Step Solution

Answer

Visualize molecules and ions distinctly for each state described.

Step 1: Understand the Molecular Composition

Lithium nitrate (\(\mathrm{LiNO}_3\)) consists of one lithium atom \(\mathrm{Li}\), one nitrogen atom \(\mathrm{N}\), and three oxygen atoms \(\mathrm{O}\). This molecule forms a compound that is often represented in solid or liquid states.

Step 2: Diagram for Solid Lithium Nitrate

For solid lithium nitrate (\(\mathrm{LiNO}_3\)), draw a series of discrete units with clearly separated spaces between them. Represent lithium, nitrogen, and oxygen atoms as distinct circles labeled \(\mathrm{Li}\), \(\mathrm{N}\), and \(\mathrm{O}\) respectively. In each molecule, the circles should slightly overlap to represent the bonded nature of the compound, with one lithium circle next to a nitrogen circle partly surrounded by three oxygen circles.

Step 3: Diagram for Molten Lithium Nitrate

In the liquid state, lithium nitrate bonds break and ions move freely. Draw this as a less ordered and more dynamic arrangement. Each molecule is now represented by separate ions: lithium ions (\(\mathrm{Li}^+\)) and nitrate ions (\(\mathrm{NO}_3^-\)). The lithium and nitrate circles should be intermixed, showing a random pattern without touching or overlapping closeness, suggesting fluidity.

Step 4: Diagram for Electrolyzed Molten Lithium Nitrate

When a direct current is applied, the ions in the molten lithium nitrate are directed towards electrodes. Draw the lithium (\(\mathrm{Li}^+\)) ions migrating towards the cathode (negative electrode) and the nitrate (\(\mathrm{NO}_3^-\)) ions moving towards the anode (positive electrode). Show the circles (ions) arranged in lines or clusters suggesting movement towards the electrodes.

Key Concepts

Nanoscale Representation

Understanding the nanoscale representation of chemical substances is crucial to visualizing their behavior at an atomic level. When illustrating molecules or compounds like lithium nitrate ( LiNO_3 ), each atom is depicted as a circle.
At the nanoscale, complexity can be simplified.

• Atoms or monoatomic ions: These are shown as individual distinct circles.
• Molecules or polyatomic ions: These overlap circles, indicating atoms bonded together.
• Different types of atoms can be differentiated by labeling the circles or using different shades.

This method helps visualize how atoms or ions are arranged in various states, whether solid, liquid, or under electric influence.

Molecular Composition

Molecular composition deals with the types and numbers of atoms in a molecule. For lithium nitrate ( LiNO_3 ), the compound consists of:

• One lithium atom ( Li )
• One nitrogen atom ( N )
• Three oxygen atoms ( O )

In its solid form, the atoms in LiNO_3 are bonded in a specific arrangement. The lithium atom is closely associated with the nitrate ion ( NO_3^- ). This composition is depicted by overlapping circles in nanoscale diagrams.
Overlapping signifies the chemical bonds that hold these atoms together in one unit.

Ion Movement

Ion movement is a critical concept in understanding reactions and states of compounds. In its molten state, lithium nitrate ( LiNO_3 ) becomes a mix of freely moving ions:

• LiNO_3 splits into lithium ions ( Li^+ ) and nitrate ions ( NO_3^- ).
• These ions move randomly, unlike the ordered arrangement in solids, representing the fluidity of the liquid state.

When a direct electric current is applied, these ions experience directed movement. Lithium ions ( Li^+ ) are attracted to the cathode (negative electrode), while nitrate ions ( NO_3^- ) move towards the anode (positive electrode). This movement can be illustrated by the alignment of ions in nanoscale diagrams as they travel to their respective electrodes.