Overview
The transcript explains metallic bonding, delocalized electrons, and why metals conduct electricity and heat. It also reviews mechanical properties and melting points of selected metals.
Metallic Bonding: Core Ideas
- Metallic bonding involves shared valence electrons among many metal cations.
- Electrons are delocalized; they are free to move and not bound to one atom.
- Core electrons are localized; they remain attached to their specific atom.
- The electron sea model: metal cations in a lattice surrounded by a sea of valence electrons.
Delocalized vs. Localized Electrons
- Delocalized electrons: free-moving valence electrons shared among many atoms.
- Localized electrons: core electrons restricted to their local atomic environment.
- Delocalization explains electrical and thermal conductivity in metals.
Electrical Conductivity in Metals
- Electricity is movement of electric charge through a material.
- Free-flowing charges enable conduction; in metals these are electrons.
- In salt water, free ions move; in metals, free electrons move.
Random Motion vs. Directed Current
- Inside a metal without voltage, electron motion is random with no net flow.
- Applying a voltage creates an electric field across the metal.
- Electric field direction: from positive side to negative side across the metal.
- Negative charges (electrons) accelerate opposite the field, toward the positive terminal.
- Metal cations are fixed; only electrons move to create current.
Role of a Battery
- A battery provides voltage that sets up an electric field in the metal.
- The field causes existing electrons in the metal to drift in one direction.
- The battery does not supply electrons; electrons are already present in the metal.
Physical Properties of Metals
- Malleable: can be hammered into thin sheets, exemplified by aluminum foil.
- Ductile: can be pulled into thin wires, often seen with copper and silver wires.
- Thermal conductors: high thermal conductivity due to mobile valence electrons.
- Electrical conductors: mobile electrons enable electrical current flow.
- Luster: metals typically have a shiny appearance.
Melting Points of Selected Metals
- Melting points of metals vary widely; most are high, some are low.
| Metal | State at Room Temp. | Approx. Melting Point (°C) | Remark |
|---|
| Mercury | Liquid | −38 to −39 | Unusually low melting point |
| Gallium | Solid | ~30 | Melts with small amount of heat |
| Zinc | Solid | ~420 | Relatively low for a metal |
| Copper | Solid | ~1085–1086 | Much higher than zinc |
| Tungsten | Solid | ~3400 | Very high melting point |
Key Terms & Definitions
- Metallic bonding: bonding where valence electrons are shared among many metal cations.
- Electron sea model: depiction of delocalized electrons surrounding fixed metal cations.
- Delocalized electrons: valence electrons free to move and shared across many atoms.
- Localized electrons: core electrons confined to their parent atom.
- Malleable: property allowing metals to be hammered into thin sheets.
- Ductile: property allowing metals to be drawn into thin wires.
- Electric field: region that exerts force on charges; drives electron drift under voltage.
- Electricity: movement of electric charge through a material.
Action Items / Next Steps
- Review electron sea model to connect delocalization with conductivity.
- Practice distinguishing delocalized versus localized electrons in metals.
- Memorize examples and melting points to illustrate variability among metals.