电子Electron

中性原子中电子数等于质子数。电子按能量分布在不同的电子层和轨道上，最外层电子（价电子）参与成键。原子失去电子形成阳离子，得到电子形成阴离子；原子之间共用电子对形成共价键，金属中离域电子形成金属键并使金属导电。

In a neutral atom the number of electrons equals the number of protons. Electrons are arranged by energy in shells and orbitals, and the outermost (valence) electrons take part in bonding. Atoms that lose electrons form cations and those that gain electrons form anions; shared electron pairs form covalent bonds, and delocalised electrons in metals form metallic bonding and carry electric current.

电子的自旋量子数为 ½，属于费米子，因此遵守泡利不相容原理，同一轨道最多容纳两个自旋相反的电子。电子在电场中向正极偏转，在磁场中也会偏转，由偏转程度可以测定其荷质比。电子同时具有波动性，电子衍射和电子显微镜都利用了这一点。

The electron has spin ½ and is a fermion, so it obeys the Pauli exclusion principle: at most two electrons of opposite spin share an orbital. Electrons are deflected towards the positive plate in an electric field and also bend in a magnetic field; the deflection gives their charge-to-mass ratio. Electrons also behave as waves, which is the basis of electron diffraction and the electron microscope.

1897 年 J. J. 汤姆孙研究阴极射线，发现它由比原子小得多、带负电的粒子组成，测得其荷质比，这是人类发现的第一种亚原子粒子。1909 年起密立根用油滴实验精确测定了电子电荷。“electron”一词由斯托尼于 1891 年提出，最初指电荷的基本单位。

In 1897 J. J. Thomson, studying cathode rays, showed they consist of negatively charged particles much smaller than atoms and measured their charge-to-mass ratio; this was the first subatomic particle discovered. From 1909 Millikan's oil-drop experiment measured the electron's charge precisely. The word electron was coined by Stoney in 1891, at first for the basic unit of charge.