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Chemical Bonding - Metallic Bonding

Grade 9IB

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Metallic bonding is defined as the electrostatic attraction between a regular lattice of positive metal ions (cationscations) and a 'sea' of delocalized electrons.

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The valence electrons are not associated with any specific atom; they are 'delocalized' and are free to move throughout the entire 3D3D giant metallic lattice.

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Metals are excellent conductors of electricity and heat because the delocalized electrons can move and carry charge or thermal energy through the structure.

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Malleability and ductility occur because the layers of metal cations can slide over each other without breaking the metallic bond, as the 'sea' of electrons adjusts to the new positions.

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The strength of the metallic bond depends on the number of delocalized electrons per atom and the charge density of the cation. For example, Al3+Al^{3+} forms stronger bonds than Na+Na^{+}.

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Metals generally have high melting and boiling points due to the strong electrostatic forces of attraction that require significant energy to overcome.

📐Formulae

M(s)→Mn++ne−M_{(s)} \rightarrow M^{n+} + ne^-

Bond Strength∝Cation ChargeIonic Radius\text{Bond Strength} \propto \frac{\text{Cation Charge}}{\text{Ionic Radius}}

Density(ρ)=massvolume\text{Density} (\rho) = \frac{\text{mass}}{\text{volume}}

💡Examples

Problem 1:

Explain why Magnesium (MgMg) has a higher melting point than Sodium (NaNa).

Solution:

MgMg has a higher melting point than NaNa because MgMg atoms donate two delocalized electrons per atom to form Mg2+Mg^{2+} ions, whereas NaNa atoms donate only one to form Na+Na^{+} ions.

Explanation:

The Mg2+Mg^{2+} ion has a higher charge and a smaller ionic radius compared to Na+Na^{+}. This results in a higher charge density, leading to a much stronger electrostatic attraction between the Mg2+Mg^{2+} cations and the sea of delocalized electrons.

Problem 2:

Why are alloys, such as steel, usually harder than pure metals like Iron (FeFe)?

Solution:

In an alloy, atoms of different sizes (e.g., Carbon in Iron) disrupt the regular arrangement of the metallic lattice.

Explanation:

In a pure metal lattice of FeFe, the layers of atoms can slide over each other easily. When different sized atoms are introduced, they lock the layers in place, making it more difficult for the layers to slide, which increases the hardness of the material.