Physical Properties of Metals

Introduction

Think of a saucepan, a copper wire, a gold ring and a steel bridge. They look and behave very differently from wood, plastic or glass, yet they share a set of features that make them unmistakably metals . Metals are shiny, conduct heat and electricity, can be bent and stretched without shattering, and are usually dense and hard to melt. These physical properties are the reason metals have shaped human technology for thousands of years.

Core explanation

Physical properties are those you can observe or measure without changing the substance into something new. Typical metals share the following:

Property What it means Example --- --- --- Lustre Shiny when freshly cut or polished Polished silver Electrical conductivity Allows an electric current to flow Copper wiring Thermal conductivity Transfers heat quickly Aluminium pans Malleability Can be hammered into sheets Aluminium foil Ductility Can be drawn into wires Copper wire High density Heavy for their size Iron 7.87 g/cm³, lead 11.3 g/cm³ High melting point Solid at room temperature Iron melts at about 1538 °C Sonorous Rings when struck A bell

A simple model. In a metal, the atoms are packed tightly together in a regular pattern. Each atom releases its outer (valence) electrons, which become delocalised : they are free to move through the whole structure. What remains is a lattice of positive metal ions surrounded by a "sea" of moving electrons. The strong attraction between the positive ions and the negative electron sea holds the metal together. This is called metallic bonding .

Explaining the properties.

- Conductivity: the delocalised electrons can drift through the metal when a voltage is applied, carrying charge. They also carry kinetic energy quickly from hot regions to cold ones, so metals are good thermal conductors. - Malleability and ductility: the ions are arranged in layers. When a force is applied, the layers can slide over one another, but the electron sea still holds them together, so the metal changes shape instead of breaking. - Lustre: the free electrons absorb and re-emit light at the surface, making it reflective. - High melting point and density: the strong metallic bonding needs a lot of energy to overcome, and the closely packed atoms put a lot of mass into a small volume.

These are typical properties. Not every metal shows all of them strongly — the Group 1 metals, for instance, are soft and have low densities — but the pattern is clear across most of the metal region of the periodic table.

Step-by-step reasoning

To explain why a metal conducts electricity:

1. State that metal atoms lose their outer electrons into a shared pool. 2. Describe these electrons as delocalised — free to move through the structure. 3. When the metal is connected to a cell, the electrons drift towards the positive terminal. 4. Moving charge is an electric current, so the metal conducts.

Visual explanation

Imagine rows of orange spheres (the positive ions) neatly stacked like oranges on a market stall, with tiny blue dots (electrons) swarming freely through all the gaps between them. Push on one side and whole rows of oranges slide along, but the blue swarm moves with them and keeps everything bonded.

Real-world analogy

A metal is like a crowd of dancers holding hands with everyone around them at once, rather than with a fixed partner. If one row shuffles sideways, the dancers simply take new hands with their new neighbours, so the crowd changes shape but never falls apart.

Real-world example

Overhead power cables are made mainly of aluminium, often with a steel core. Aluminium is a good electrical conductor, is ductile enough to be drawn into long strands, and has a low density for a metal (2.70 g/cm³), so the cables are light enough to hang between pylons.

Why?

Why does a metal bend when you hammer it, while a crystal of salt shatters? In a metal, sliding layers of ions stay attracted to the electron sea, so no bonds are lost overall. In salt, sliding the layers brings ions of the same charge next to each other; they repel, and the crystal splits.

Common misconception

"Metals conduct electricity because electrons flow in from the wire." The electrons that carry the current are already inside the metal. The power supply simply pushes the metal's own delocalised electrons along, which is why current starts flowing almost instantly around a circuit.

Worked example

Question: A sample of an unknown element is shiny, has a density of 8.9 g/cm³, bends without breaking and lets a bulb light when placed in a circuit. Is it a metal? Give three pieces of evidence.

Reasoning: Lustre, high density, malleability and electrical conductivity are all typical metallic properties. Its density is close to that of copper or nickel.

Answer: Yes — it is shiny, it conducts electricity and it is malleable (it also has a high density).

Quick check

1. Which property of copper makes it suitable for drawing into electrical wires? Answer: Ductility, together with its good electrical conductivity.

Exam focus

Learn at least five metal properties and be able to link each to a use. For explanation marks, always mention delocalised electrons for conductivity and layers of ions sliding over each other for malleability and ductility.

Advanced insight

Pure metals are often too soft for engineering, because their layers slide too easily. Adding atoms of a different size to make an alloy , such as carbon in steel or copper in gold jewellery, distorts the layers so that they cannot slide as easily. The alloy is harder and stronger than the pure metal, although it usually conducts electricity a little less well.

Summary

Metals are typically lustrous, good conductors of heat and electricity, malleable, ductile, dense, sonorous and high melting. These properties arise from metallic bonding: a lattice of positive ions held together by a sea of delocalised electrons. The free electrons explain conductivity and lustre, and the sliding layers explain why metals bend rather than break.

Practice questions

1. Explain why metals are good conductors of heat. Answer: Their delocalised electrons move freely and carry kinetic energy rapidly from hot parts of the metal to cold parts. 2. What is the difference between malleable and ductile? Answer: Malleable means it can be hammered into sheets; ductile means it can be drawn out into wires. 3. Suggest why aluminium, not iron, is used for aircraft bodies. Answer: Aluminium has a much lower density (2.70 g/cm³ compared with 7.87 g/cm³ for iron), so parts of the same size are lighter. 4. Describe the structure of a metal in terms of ions and electrons. Answer: A regular lattice of positive metal ions surrounded by a sea of delocalised electrons that holds the ions together.