金属键Metallic bonding

导电性：离域电子在电压作用下定向移动形成电流，固态和液态金属都导电。导热性：自由电子和晶格振动都能传递能量。延展性：金属受力时阳离子层可以相互滑动，离域电子随之移动，金属键并不断开，所以金属能被锻打和拉丝。金属光泽来自自由电子对光的吸收和再发射。

Conductivity: under a voltage the delocalised electrons drift in one direction, carrying current, so metals conduct both solid and molten. Thermal conductivity: free electrons and lattice vibrations both carry energy. Malleability and ductility: under stress, layers of cations can slide over each other while the electrons move with them, so the bonding is not broken and metals can be hammered and drawn into wires. Metallic lustre comes from free electrons absorbing and re-emitting light.

每个原子提供的离域电子越多、阳离子电荷越高、半径越小，阳离子与电子海之间的吸引越强，金属的熔点越高。第三周期中 Na（97.8 °C）< Mg（650 °C）< Al（660 °C）。第 1 族从上到下，原子半径增大，金属键减弱，熔点降低：Li 181 °C，Cs 28 °C。

The more delocalised electrons each atom provides, and the higher the charge and smaller the radius of the cation, the stronger the attraction and the higher the melting point. In period 3, Na (97.8 °C) < Mg (650 °C) < Al (660 °C). Down group 1 the atoms get larger and the bonding weaker, so melting points fall: Li 181 °C, Cs 28 °C.

1900 年德鲁德提出自由电子模型解释金属的导电性。量子力学建立后，索末菲改进了自由电子模型，布洛赫等人发展出能带理论：大量原子轨道组合成连续的能带，价带部分填充或与导带重叠时材料表现为金属。

In 1900 Drude proposed the free-electron model to explain electrical conduction in metals. After quantum mechanics, Sommerfeld refined the free-electron model and Bloch and others developed band theory: vast numbers of atomic orbitals combine into continuous bands, and a material is metallic when its valence band is partly filled or overlaps the conduction band.