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Difficulty: HardMetallic Bonding and Properties of Metals

Match each physical or chemical behavior of metallic substances on the left with its corresponding atomic-scale mechanism on the right.

  • High thermal conductivity under a temperature gradientRapid kinetic energy transfer by delocalized valence electrons alongside lattice vibrations
  • Decrease in electrical conductivity with increasing temperatureIncreased amplitude of cation lattice vibrations enhancing delocalized electron scattering
  • Characteristic metallic lustre when a polished surface is illuminatedOscillation of surface free electrons leading to immediate absorption and re-emission of light photons
  • Significantly higher melting points in transition metals compared to alkali metalsPresence of additional covalent bonding forces due to un-paired dd-orbital overlap alongside ss-electron delocalization

Answer

High thermal conductivity corresponds to rapid kinetic energy transfer by delocalized electrons; the decrease in electrical conductivity at higher temperatures corresponds to increased scattering from vibrating metal cations; metallic lustre corresponds to photon absorption and re-emission by surface delocalized electrons; and the higher melting points of transition metals correspond to combined ss-electron delocalization and dd-orbital overlap.
Each property is accurately matched with its fundamental physical cause: thermal conduction is driven by kinetic energy transfer by mobile electrons; thermal reduction of electrical conductivity stems from enhanced cation scattering; lustre arises from rapid light re-emission by surface electrons; and high transition metal melting points are due to combined ss-electron delocalization and dd-orbital bonding.

Step-by-Step Solution

1
Analyze the mechanism for heat conduction in metals.
Thermal conduction occurs because delocalized valence electrons move freely and quickly pass kinetic energy down the temperature gradient.
Free electrons carry kinetic energy much faster than localized lattice atom collisions alone.
2
Analyze how temperature affects electrical resistance/conductivity in metals.
Heating increases the vibrational amplitude of positive cations in the lattice, creating greater resistance (scattering) for moving electron streams.
Impeding the mean free path of drift electrons reduces electrical conductivity.
3
Analyze the optical reflection property of metals.
Incident light causes surface delocalized electrons to oscillate and instantly re-radiate light photons across continuous energy levels.
The sea of mobile electrons acts as a reflective barrier to light waves.
4
Compare cohesive energy differences between alkali metals and transition metals.
Transition elements utilize both outer ss valence electrons and partially filled inner dd subshells to form additional covalent bonds, significantly increasing lattice strength and melting point.
Greater electrostatic attraction and inter-atomic orbital overlap increase the energy required to break the lattice.

Key Concept

Metallic Bonding mechanisms relating atomic-scale electron sea and lattice structures to macroscopic physical properties
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Topics

Metallic Bonding and Properties of Metals

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