Metallic Bonding and Structures

The strength of a metallic bond depends on two main factors: the magnitude of the positive charge on the metal ion, and the number of delocalised electrons contributed by each atom.

Worked Example

Compare the melting points of Sodium and Magnesium to determine which has the stronger metallic bonding.

Step 1: Identify the groups and the ions formed.

• Sodium ($Na$) is in Group 1. It forms $Na^+$ ions, so each atom contributes one delocalised electron to the sea.
• Magnesium ($Mg$) is in Group 2. It forms $Mg^{2+}$ ions, so each atom contributes two delocalised electrons.

Step 2: Compare the charges and electron quantities.

• The $Mg^{2+}$ ions have a higher positive charge than the $Na^+$ ions.
• There are also twice as many delocalised electrons in the magnesium lattice compared to the sodium lattice.

Step 3: Conclude on the bond strength.

• The electrostatic attraction between the higher-charged $Mg^{2+}$ ions and the denser sea of delocalised electrons is much stronger than in sodium.
• Therefore, magnesium requires more thermal energy to break its metallic bonds, resulting in a higher melting point.

Physical Properties of Metals

Metals are excellent electrical and thermal conductors in both their solid and liquid states. The delocalised electrons act as mobile charge carriers that are free to move and transfer electrical charge or heat energy rapidly through the entire lattice.

Pure metals are also malleable (can be hammered into shape) and ductile (can be drawn into wires). Inside the lattice, the positive metal ions are arranged in regular layers. When a force is applied, these layers can slide over each other. The metallic bonds do not break when the layers shift because the delocalised electrons simply move to maintain the electrostatic attractions.

Comparing Primary Bonds

Metallic, ionic, and covalent bonds are all primary bonds held together by electrostatic attraction. However, the exact particles involved and the nature of the attraction differ significantly.