Yes, metals conduct electricity because each metal atom releases one to three outer electrons into a shared "sea" of delocalized charge carriers. These free electrons move under an applied voltage, and a typical metal carries that current at a conductivity of about 10 million siemens per meter (MS/m). That figure is roughly 10^20 times higher than glass and up to a billion times higher than dry air. Copper's conductivity of 59.6 MS/m at 68°F (20°C) puts it among the best practical conductors on Earth.
The mechanism: why metal atoms give up their electrons
A metal atom has loosely bound valence electrons sitting in its outermost shell. In a solid lattice, each atom donates one or more of these electrons to a shared band that spans the whole crystal. This is the free-electron model, formalized in 1900 by Paul Drude and refined by Arnold Sommerfeld in 1927.
The donated electrons no longer belong to any single atom. They form a partially filled conduction band. Because that band is only partly occupied, an applied electric field can nudge electrons into slightly higher energy states. They accelerate, drift as a group, and deliver charge through the metal.
In plain terms: the electrons were never tightly held, so a voltage gives them an easy path forward.
For context, a single copper wire one millimeter in diameter carries about 8.5 × 10^22 free electrons per centimeter of length. That density, measured at roughly 10^23 carriers per cubic centimeter, is why metals respond to voltage almost instantly.
How conduction differs from insulation: the band gap
The key variable is not whether electrons exist but whether they can move into empty states. In an insulator like diamond, the valence band is full and the next empty band sits far away. Electrons need an energy boost of about 5.5 electron volts (eV) to cross that gap. At room temperature, almost none can.
In a semiconductor like silicon, the gap is much smaller, about 1.1 eV. A few electrons cross it, so conduction happens but is weak. In a metal like copper, no gap exists at all. The conduction band overlaps or runs partly empty.
In plain terms: an insulator is a locked stairwell, a semiconductor is a low step, and a metal is an open door.
Quantified comparison: metals, semiconductors, and insulators
The table below uses room-temperature conductivity in siemens per meter (S/m). One siemens is one ampere per volt.
| Material | Class | Conductivity (S/m) | Free-electron behavior |
|---|---|---|---|
| Silver | Metal | 63 MS/m | Best conductor, highest electron mobility |
| Copper | Metal | 59.6 MS/m | Near-silver performance, far cheaper |
| Gold | Metal | 45 MS/m | Corrosion-resistant, lower conductivity than copper |
| Aluminum | Metal | 37.8 MS/m | Lighter, ~63% of copper's conductivity |
| Iron | Metal | 10.4 MS/m | Magnetic, roughly one-sixth of copper |
| Tap water | Conductive liquid (ionic) | 0.005-0.05 S/m | Ions carry charge, not free electrons |
| Silicon (pure) | Semiconductor | 0.0004 S/m | Requires doping or heat to conduct |
| Glass | Insulator | 1 × 10^-11 S/m | Effectively zero at room temperature |
| Air (dry) | Insulator | 1 × 10^-14 S/m | Breaks down only at ~3,000 volts per millimeter |
The spread between silver and glass is about 15 orders of magnitude. The spread between copper and dry air is nearer 19 orders. Those are not small differences; they are the entire reason we route power through metal and insulate around it.
Silver conducts about 5% better than copper. Gold conducts roughly 24% worse than copper. Yet gold is standard for electrical contacts because it does not tarnish. That trade-off matters more than raw conductivity in many real designs.
Why some metals conduct better than others
Three factors set a metal's conductivity. The first is valence-electron count. More donated electrons per atom means more carriers. Aluminum contributes three per atom; copper contributes one.
The second is how regularly the atoms sit in the lattice. Scattering events interrupt electron drift. Each collision costs momentum and adds resistance. Iron and nickel, with more complex atomic structure, scatter electrons more.
The third is temperature. Lattice vibration grows with heat, and that vibration is the main scattering source in ordinary metals. As temperature rises, conductivity falls.
In plain terms: more carriers and a smoother lattice give you a better conductor.
Silver and copper, both with one valence electron and clean face-centered cubic lattices, sit near the top for that reason. Aluminum's extra carriers partly offset its higher scattering rate.
The temperature and purity edge cases
For most metals, resistance rises roughly linearly above room temperature, and resistivity climbs about 0.4% per degree Celsius for copper. A 100°F temperature increase can nearly double copper's resistance.
This is why engine wiring and rooftop solar cables are sized generously. The diameter chosen for room temperature may fail a voltage-drop check at a hot operating point.
Purity matters just as much. A tiny alloy addition can wreck conductivity. Adding 1% chromium to copper drops its conductivity from 100% IACS to about 80% IACS. Even a few tenths of a percent of phosphorus can push copper below 90% IACS. IACS means International Annealed Copper Standard, where 100% equals pure copper.
At the extreme cold, a surprising thing happens. Below about 30 kelvin, many metals lose all resistance and become superconductors. Mercury, lead, and aluminum all do this. Their conductivity is not merely high; it becomes effectively infinite, sustained by paired electrons.
Common misconceptions about metal conduction
Several myths deserve a correction.
- Myth: electrons move at nearly the speed of light. Reality: free electrons drift at well under one millimeter per second. The signal itself travels near light speed because the field propagates through the whole electron sea at once.
- Myth: thicker metal always conducts better. Reality: thickness lowers resistance, but conductivity is an intrinsic property independent of size. A thin pure-silver film can beat a thick steel plate.
- Myth: all good conductors are metals. Reality: graphite conducts well through delocalized pi electrons, and many ionic solutions conduct via ions. Neither has a metal lattice.
- Myth: heated metal is a better conductor. Reality: for normal metals, heat lowers conductivity. Only semiconductors partly reverse this behavior.
- Myth: current travels inside the metal as a steady stream of one set of electrons. Reality: every electron in the sea participates, all drifting together slowly.
In plain terms: the common picture of fast electrons is wrong. The metal is fast; the electrons are slow.
What actually determines wire choice and safety
Engineers do not pick metals on conductivity alone. Cost, weight, corrosion, and thermal limits all compete. Aluminum, at roughly 63% of copper's conductivity but one-third the density, dominates overhead power lines. Copper dominates building wiring and motors where space is tight.
Concrete rules follow from the numbers. A wire sized for 20 amperes at 86°F must be upsized if it runs at 149°F. Joining copper to aluminum requires special connectors, because their differing expansion rates loosen plain screw terminals and create hot spots.
Here is what to actually do when working with conductivity:
- Choose copper for space-constrained or safety-critical runs, and aluminum for long overhead spans.
- Upsize any conductor expected to run above its reference temperature, using the 0.4% per degree Celsius copper figure as a starting correction.
- Verify that terminals installed on aluminum are rated for aluminum, since mismatched connectors are a documented failure point.
- Measure conductivity with a four-wire ohmmeter, not a two-wire meter, when the resistance under test is below one ohm.
- Treat any conductor reading above 100% IACS with suspicion; that usually signals measurement error, not a superconductor.
The limits of the free-electron picture
The free-electron model explains most of what you will ever need. It does not explain everything. It cannot fully predict why measured conductivities vary between samples of the same metal.
Real metals have grain boundaries, impurities, and defects that scatter electrons. Lattice vibration and defect scattering add together, which is encapsulated in Matthiessen's rule: total resistivity equals the sum of impurity and thermal contributions.
The model also breaks down for transition metals and for superconductors, where interactions between electrons dominate. These are active research areas, not settled textbook facts. What is settled is the broad mechanism: delocalized electrons, a partly empty conduction band, and a scattering-limited drift.
The scientific consensus, traceable from Drude in 1900 through the quantum band theory of the 1930s, is firm on the core answer. Metals conduct because their electrons are shared, mobile, and unconstrained by a band gap. Everything else is a matter of how well, how hot, and how pure.