# Metallic Bonding

> Positive ions in a sea of electrons, why metals conduct and bend, and how alloys make metals stronger.

From HSC Chemistry on WhizzNotes, free study notes for NSW students: https://whizznotes.com/chemistry/metallic-bonding/. Updated 3 November 2026.
Year 11 and Year 12 boxes go deeper than the Year 10 text around them.

### Story time: The copper wire and the clay pot
Zara's grandfather was an electrician. He could bend a copper wire into any shape with his fingers, and it never cracked. Then he plugged it into a circuit and it carried electricity to a light.

Zara's grandmother was a potter. If she dropped one of her fired clay pots, it shattered into pieces, and no electricity would ever flow through it.

Why do metals bend instead of breaking, and why do they carry electricity so easily? The answer is a special kind of bond where the electrons are not owned by any one atom at all.

**In short:** A metallic bond is the attraction between positive metal ions and a sea of free (delocalised) electrons. The free electrons let metals conduct electricity and heat, and layers of ions can slide, so metals bend without breaking. Alloys mix in other atoms to make metals harder.

## The sea of electrons

In a metal, each atom lets go of its **valence electrons**. What is left behind are **positive metal ions** packed in neat rows, called a **metallic lattice**.

The released electrons are **delocalised**: they are free to move through the whole metal. We call them a **sea of electrons**.

The **metallic bond** is the attraction between the positive metal ions and the sea of delocalised electrons around them.

*Diagram: Rows of positive metal ions surrounded by a sea of free electrons*
*Positive ions in fixed rows. The red electrons can move anywhere through the metal.*

## Explaining the properties of metals

| Property | Explanation |
|---|---|
| **Conduct electricity** | Delocalised electrons are free to move and carry charge through the metal |
| **Conduct heat** | Free electrons carry energy quickly from hot parts to cold parts |
| **Malleable** (can be hammered into sheets) and **ductile** (can be drawn into wires) | Layers of ions can slide over each other. The sea of electrons moves with them, so the bond is not broken |
| **High melting and boiling points** (most) | The attraction between ions and electrons is strong and acts in all directions |
| **Shiny** (lustrous) | Free electrons reflect light |
| **High density** (most) | Ions are packed very closely |

### Key idea: Why metals bend but salt shatters
In salt, sliding a layer lines up like charges, $+$ next to $+$, and they repel, so the crystal breaks. In a metal, every ion is positive and the electrons simply flow into the new positions. There is no repulsion, so the metal bends instead.

## Alloys

An **alloy** is a mixture of a metal with at least one other element, usually another metal (or carbon).

Pure metals are often too soft, because their layers slide easily. In an alloy, atoms of different **sizes** sit among the metal ions and **disrupt the layers**, so they cannot slide as easily. The alloy is **harder and stronger**.

| Alloy | Made from | Used for |
|---|---|---|
| **Steel** | Iron + a little carbon | Buildings, bridges, cars |
| **Stainless steel** | Iron + chromium + nickel | Cutlery, sinks (does not rust) |
| **Bronze** | Copper + tin | Statues, medals |
| **Brass** | Copper + zinc | Door handles, musical instruments |
| **Solder** | Tin + other metals (traditionally lead) | Joining wires in electronics |
| **18 carat gold** | Gold + copper and silver | Jewellery (pure gold is too soft) |

*Diagram: Left: a pure metal with even layers that slide. Right: an alloy where a larger atom disrupts the layers*
*A different sized atom jams the layers, making the alloy harder.*

### Watch out: Alloys are mixtures, not compounds
The metals in an alloy are mixed, not chemically joined in a fixed ratio. That is why steel can contain 0.1% carbon or 1.5% carbon and still be steel.

### Exam tip: Exam wording
When explaining conduction in metals, always use the words **delocalised electrons** and **free to move**. "Metals have electrons" is not enough for full marks.

**Mind map**

```text
Metallic bonding
  Structure
    Positive ions in a lattice
    Sea of delocalised electrons
    Attraction ions to electrons
  Properties
    Conduct electricity and heat
    Malleable and ductile
    High melting point
    Shiny
  Alloys
    Mixture of metals
    Layers disrupted
    Harder, stronger
    Steel, bronze, brass
```

### Year 11: Comparing metals
The strength of metallic bonding depends on:

- **How many electrons each atom gives to the sea**: more delocalised electrons and a bigger ion charge mean a stronger bond.
- **Ion size**: smaller ions are held more tightly.

Sodium gives 1 electron per atom and melts at 98 °C. Magnesium gives 2 and melts at 650 °C. Aluminium gives 3 and melts at 660 °C. Going **down group 1**, the ions get bigger, so the metallic bond weakens and melting points **fall**: lithium 181 °C, sodium 98 °C, potassium 63 °C.

### Year 12: Band theory in brief
In a large lattice, the outer orbitals of billions of metal atoms merge into **energy bands**. In metals, the highest filled band overlaps with an empty band, so electrons can move into empty energy levels with almost no extra energy. That is why metals conduct.

In an **insulator** there is a large **band gap** between the full band and the empty band. In a **semiconductor** like silicon, the gap is small, so heat or light can lift some electrons across. Adding tiny amounts of other elements (**doping**) controls this, which is the basis of every computer chip and solar cell.

## Quick summary

- A metallic bond is the attraction between **positive metal ions** and a **sea of delocalised electrons**.
- Free electrons explain conduction of electricity and heat, and the shine of metals.
- Layers of ions slide without breaking the bond, so metals are malleable and ductile.
- **Alloys** mix a metal with other elements. Different sized atoms stop layers sliding, so alloys are harder and stronger.
- Examples: steel (iron and carbon), bronze (copper and tin), brass (copper and zinc).

## Quiz

Try these questions from the chapter quiz.

1. A metallic bond is the attraction between:
   - A. Two non-metal atoms sharing electrons
   - B. Positive and negative ions
   - C. Positive metal ions and delocalised electrons
   - D. Neutrons and electrons
   - Answer: C. Positive metal ions and delocalised electrons. The sea of electrons holds the positive ions together.

2. Why can metals conduct electricity when solid?
   - A. They have delocalised electrons that are free to move
   - B. Their ions are free to move
   - C. They contain water
   - D. Their protons move
   - Answer: A. They have delocalised electrons that are free to move. Free electrons carry the charge through the metal.

3. A metal that can be hammered into thin sheets is:
   - A. Ductile
   - B. Malleable
   - C. Brittle
   - D. Lustrous
   - Answer: B. Malleable. Malleable means it can be hammered into shape. Ductile means drawn into wires.

The whole chapter quiz is on the page, for signed-in students: https://whizznotes.com/chemistry/metallic-bonding/#quiz