# Metallic bond

> Positive ions in a sea of electrons


## Objectives

- Describe the metallic bond: positive ions held together by free valence electrons.
- State that, for neighbours such as Na, Mg and Al, more free valence electrons per atom give a stronger metallic bond and a higher melting point.
- Use the bond to explain why metals conduct electricity and can be hammered into shape.

## 1. General properties: mass, radius and metallic property




## 2. Neighbours, very different

Predict: why does magnesium hold together so much more strongly?

- Each magnesium atom gives more electrons to the bond ✓
- Magnesium atoms share electron pairs, like $\ce{Cl2}$
- Magnesium atoms are much heavier

Each magnesium atom releases 2 valence electrons into the sea, while each sodium atom releases 1. More free electrons hold the positive ions more strongly, so the metallic bond of magnesium is stronger and it melts at a higher temperature.

[ar-EG] كل ذرة magnesium بتحرّر 2 valence electrons في البحر، وكل ذرة sodium بتحرّر 1. والـ free electrons الأكتر بتمسك الـ positive ions بقوة أكبر، فالـ metallic bond بتاع الـ magnesium أقوى وبينصهر عند درجة حرارة أعلى.
## 3. A sea of electrons

Sodium: positive ions in a regular pattern (a crystal lattice), in a sea of free electrons Metallic bond The attraction between the positive metal ions and the free valence (outer) electrons around them. Each atom releases its valence electrons. They move freely among the ions and hold them together.


## 4. More electrons, stronger bond

Choose the number of valence electrons each atom releases. Watch the sea and the melting point. valence electrons per atom Na: ions of charge +, 1 free electron(s) per atom Na melting point Na boiling point Mg: ions of charge 2+, 2 free electron(s) per atom Mg melting point Mg boiling point Al: ions of charge 3+, 3 free electron(s) per atom Al melting point Al boiling point For neighbours such as Na, Mg and Al: more free electrons per atom → a stronger metallic bond → higher melting and boiling points.


## 5. What the sea explains

The same free electrons explain two familiar metal properties. One sea of electrons, two metal properties Conducts electricity The free electrons can move through the metal and carry the current. Can be hammered Layers of ions can slide over each other. The sea of electrons still holds them, so the metal bends instead of breaking.


## 6. A new pair

Potassium (1 valence electron) melts at 63 °C. Calcium (2 valence electrons) melts at 842 °C. Which explains the difference?

- Calcium atoms are much heavier
- Calcium releases more free electrons per atom, so its metallic bond is stronger ✓
- Calcium atoms share electron pairs, like a non-metal

Calcium releases 2 free electrons per atom and potassium 1, so the metallic bond of calcium is stronger and its melting point is higher. Their masses (40 and 39) are almost the same, and metal atoms do not share electron pairs.

[ar-EG] الـ calcium بيحرّر 2 free electrons لكل ذرة والـ potassium بيحرّر 1، فالـ metallic bond بتاع الـ calcium أقوى والـ melting point بتاعه أعلى. كتلتهم (40 و 39) تقريبًا واحدة، والـ metal atoms مش بتشارك في أزواج electrons.
## 7. Summary

Metallic bond: positive metal ions held together by a sea of free valence electrons. For neighbours such as Na, Mg and Al: more free electrons per atom → stronger bond → higher melting and boiling points. The free electrons conduct electricity; sliding layers make metals easy to shape. Next in Chapter 1: in transition metals, both 4s and 3d electrons can join this bond. Na, Mg, Al: more free electrons, higher melting and boiling points Can you explain why magnesium melts at a much higher temperature than sodium?



Chapter: Transition Elements (https://yaani.ai/en/learn/chemistry/chem-s3-en.ch1)
Source: https://yaani.ai/en/lesson/chem-s3-en.lesson-bond.metallic-bond