原子核对最外层电子的作用受到屏蔽。
这些元素，不像过渡金属那样显示出可变的化合价，他们只有最外层电子参加反应。
These elements, unlike the transition elements, do not exhibit variable oxidation states, and their valence electrons are only present in their outer shell.
所有的稀有气体元素的最外层电子数都是该层最大的可能数目：氦的最外层电子有两个，其它的稀有气体最外层电子数是八。这使稀有气体非常稳定。
All noble gases have the maximum number of electrons possible in their outer shell (two for helium, eight for all others), making them highly stable.
这个最外层被称作价电子层。
要记得，我们讨论的只是价电子，也就是最外层的电子。
And remember, we're only talking about valence electrons, so the outer-most shells.
一个原子的许多性质都是由其最外层的电子所确定的。
Many properties of an atom are determined by the outermost electrons.
现在大家都知道元素的性质主要取决于元素原子的最外层能级的电子数目。
It is now known that properties of an element depend mainly on the number of electrons in the outermost energy level of the atoms of the element.
镁原子的最外层有多少电子？
原子内第三层和最外层之间的一些电子层，含有多达32个电子。
Some layers between the third and last layers of an atom contain as many as 32 electrons.
原子内第三层和最外层之间的一些电子层，含有多达32个电子。
Some layers between the third and last layers of an atom contain as many as 32 electrons.
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