In metallic solids, electrical conductivity mainly results from the metal atoms having which characteristic property?

Introduction / Context:
Metals are known for their ability to conduct electricity, which is why they are used in wires, cables, and electrical contacts. This question tests your understanding of the microscopic reason behind metallic conductivity, focusing on which property of metal atoms explains this behaviour.

Given Data / Assumptions:
- We are considering typical metallic solids such as copper, aluminium, and silver.
- Metal atoms have valence electrons that are less tightly held than those in non metals.
- Electrical conductivity requires charged particles that can move freely through the material.

Concept / Approach:
In a metallic solid, valence electrons are not confined to individual atoms. Instead, they become delocalised and can move throughout the crystal lattice. This situation is often described as a sea of electrons surrounding positive metal ion cores. When a potential difference is applied, these mobile electrons drift in a particular direction, creating electric current. The high mobility of these valence electrons is the fundamental reason metals conduct electricity so well.

Step-by-Step Solution:
Step 1: Recall that electrical conduction requires mobile charge carriers inside a material. Step 2: In metals, the outermost electrons are loosely held and can move freely between atoms. Step 3: These delocalised electrons form an electron cloud or electron sea that extends throughout the metal lattice. Step 4: When an electric field is applied, the mobile electrons drift, producing an electric current. Step 5: Therefore, the correct explanation is that metals have highly mobile valence electrons that can move through the lattice.

Verification / Alternative check:
Models such as the free electron model and band theory of solids both describe conduction in metals in terms of electrons that can move easily from atom to atom. Measurements of conductivity correlate strongly with the availability of such mobile electrons. Additionally, the fact that metals become less conductive when heated, due to increased scattering of electrons, further supports the picture of mobile electron carriers rather than moving positive ions or fixed electrons.

Why Other Options Are Wrong:
- Very high electronegativity: Metals actually have relatively low electronegativity; high electronegativity is characteristic of non metals, which generally do not conduct as well as metals in solid form.
- Extremely high ionization energy: Metals have lower ionization energies than non metals, which allows their valence electrons to delocalise; high ionization energy would hinder conduction.
- Highly mobile protons in the nucleus: Protons are bound within nuclei and do not move through the lattice; they are not charge carriers in metallic conduction.
- Fixed electrons that cannot move between atoms: If electrons were fixed, the metal would be an insulator rather than a conductor.

Common Pitfalls:
Some learners confuse the roles of ions and electrons in conduction, especially after learning about electrolysis in solutions where ions carry current. In solid metals, however, it is the electrons that move. Another mistake is thinking that high electronegativity or ionization energy helps conduction, when in fact the opposite is true for metallic behaviour. Focusing on mobile valence electrons as the carriers of current helps clarify these differences.

Final Answer:
Electrical conductivity in metals mainly results from Highly mobile electrons in the valence shell that can move through the lattice.