Conductivity and Reflectivity

Summary

This video explores two key properties of materials with lattice structures: electrical conductivity and reflectivity. It explains that conductivity requires mobile charged particles, highlighting three cases: metallic bonding with delocalized electrons, dissolved ionic compounds where ions become mobile in water, and molten ionic compounds. Non-ionic compounds, like sugar, do not conduct electricity. The video also examines why metals are highly reflective, showing that weakly held surface valence electrons vibrate with incoming light, reflecting it efficiently. Examples like aluminum and gold illustrate how reflection determines metallic appearance, while non-metals lack this property due to strongly held electrons.

Takeaways

• 😀 Conductivity refers to the ability of a substance to conduct electricity by allowing charged particles (electrons or ions) to move through it.
• 😀 In physics, current flows from positive to negative, but in chemistry, the focus is on the movement of electrons from negative to positive.
• 😀 Metallic bonding involves delocalized valence electrons, which are free to move through the metal, allowing it to conduct electricity.
• 😀 A solid ionic compound does not conduct electricity because its ions are locked in place within the crystal lattice and cannot move.
• 😀 When an ionic compound is dissolved in water, the ions are separated and become mobile, allowing the solution to conduct electricity.
• 😀 Non-ionic compounds like sugar do not conduct electricity when dissolved in water because they do not dissociate into ions.
• 😀 Molten ionic compounds can conduct electricity because the heat breaks down the solid lattice, allowing ions to move freely.
• 😀 Metals are highly reflective because their delocalized electrons vibrate at the same frequency as incoming light, reflecting it back.
• 😀 The color of light reflected by a metal depends on how its delocalized electrons interact with different wavelengths of light.
• 😀 Gold reflects light in the 550-700 nanometer range, which explains its yellowish color, as it reflects red, orange, and yellow light the best.
• 😀 The weakly held valence electrons in metals allow them to reflect light more effectively than non-metals, which hold their electrons more tightly.

Q & A

What is electrical conductivity and why does it require mobile charges?

Electrical conductivity is the ability of a substance to allow electric current to flow. It requires mobile charges, such as electrons or ions, because current is the movement of charged particles through a material.

How do physicists and chemists define current flow differently?

Physicists define current as flowing from the positive to the negative terminal, while chemists track the actual movement of electrons, which flow from the negative to the positive terminal.

Why can metals conduct electricity?

Metals conduct electricity because they have delocalized valence electrons that are free to move throughout the metallic lattice, providing mobile charge carriers.

Why do solid ionic compounds not conduct electricity?

Solid ionic compounds do not conduct electricity because their ions are locked in place within the crystal lattice and cannot move freely.

How do dissolved ionic compounds conduct electricity?

When ionic compounds are dissolved in water, the water molecules separate the ions, making them mobile. These free ions can move towards the electrodes when a voltage is applied, allowing the solution to conduct electricity.

Why does sugar not conduct electricity when dissolved in water?

Sugar is a covalent compound with no ions. Even when dissolved, it does not produce mobile charged particles, so it cannot conduct electricity.

Under what condition can molten ionic compounds conduct electricity?

Molten ionic compounds conduct electricity because heating separates the ions, allowing them to move freely and carry electric current.

Why are metals highly reflective compared to non-metals?

Metals are highly reflective because their weakly held valence electrons can vibrate at the frequency of incoming light and re-emit it, causing reflection. Non-metals have strongly held electrons that do not respond similarly, resulting in low reflectivity.

Why does gold appear gold-colored while aluminum appears silver?

Gold reflects light mainly in the 550–700 nm range (yellow to red), giving it a gold appearance. Aluminum reflects almost all visible wavelengths, making it appear shiny silver.

What role do delocalized electrons play in both conductivity and reflectivity of metals?

Delocalized electrons provide mobile charges for conductivity, and weakly held surface electrons can oscillate in response to incoming light, reflecting it. This dual role explains why metals are both conductive and reflective.

What is the relationship between ionic mobility and conductivity in solutions?

The greater the mobility of ions in a solution, the higher the conductivity. Dissolved ions move toward electrodes under an electric field, allowing current to flow.

Why are covalent compounds generally poor conductors of electricity?

Covalent compounds do not have free ions or delocalized electrons, so they lack mobile charge carriers, making them poor conductors even when dissolved.