元素周期表简介
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元素周期表
元素介绍
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元素

化学元素（Chemical element）就是具有相同的核电荷数（核内质子数）的一类原子的总称，从哲学角度解析，元素是原子的质子数目发生量变而导致质变的结果。
常见元素有氢，氧，氮和碳等。2019年为止，共有118种元素被发现，其中94种存在于地球上。拥有原子序数≥83（铋元素及其后）的元素的原子核都不稳定，会发生衰变。第43和第61种元素（锝和钷）没有稳定的同位素，会进行衰变。自然界现存最重的元素是94号钚。

What is an element
元素是什么?
Elements are pure substances that are made up of only one type of atom such as hydrogen carbon or mercury.
元素是由仅一种类型的原子组成的纯物质,如氢、碳或汞·
So what makes one element different from another
那么,是什么使得不同的元素彼此不同呢?
Well it's the number of protons in a single atom of an element.
它们的区别在于每个元素的原子中质子的数量·
This is called the element's atomic number.
这个数字叫做元素的原子序数·
For example hydrogen has one proton in its nucleus so its atomic number is one.
例如,氢的原子核中有一个质子,所以它的原子序数是1·
Carbon has six protons so its atomic number is six.
碳有六个质子,所以它的原子序数是6·
And mercury's atomic number is 80 because it has 80 protons in its nucleus.
汞的原子序数是80,因为它的原子核中有80个质子·
Since the nucleus contains almost the entire mass of an atom the number of particles it contains has a big effect on the atom's mass.
由于原子核几乎包含了原子的大部分质量,因此它所包含的粒子数量对原子的质量有很大的影响·
Each positively charged proton has a mass unit of one and each neutral neutron also has a mass unit of one.
每个带正电的质子质量单位为1,每个中性中子的质量单位也为1·
The total number of protons and neutrons in the nucleus of an atom is called the mass number.
原子核中质子和中子的总数称为质量数·
In this example the mass number of a hydrogen atom is one.
在这个例子中,氢原子的质量数是1·
Hydrogen is the only element that usually doesn't have any neutrons.
氢是唯一通常没有中子的元素·
The mass number of this carbon atom with six protons and six neutrons is 12.
这个碳原子的质量数是12,因为它有六个质子和六个中子·
And the mass number of this mercury atom with 80 protons and 121 neutrons is 201.
这个汞原子的质量数是201,因为它有80个质子和121个中子·
Needless to say mercury is a much heavier element than hydrogen or carbon.
不用说,汞是比氢或碳重得多的元素·
Even though every atom of the same element always has the same number of protons sometimes an element has atoms with different numbers of neutrons.
尽管同一种元素的每个原子总是有相同数量的质子,但有时元素的原子会有不同数量的中子·
Ordinary hydrogen has no neutrons but there's a version of hydrogen with one neutron and another version with two neutrons.
普通氢没有中子,但氢有一种含一个中子的版本,还有一种含两个中子的版本·
Atoms of the same element with different numbers of neutrons are called isotopes.
具有不同中子数的同一元素的原子叫做同位素·
The three isotopes you see here are all still hydrogen because they all have only one proton.
这里看到的三种同位素仍然是氢,因为它们都有且只有一个质子·
Since neutrons have about the same mass as protons isotopes of the same element have different mass numbers.
由于中子的质量与质子相近,因此同一元素的同位素具有不同的质量数·
In fact an element's isotopes are often identified by their mass numbers.
事实上,元素的同位素通常通过它们的质量数来识别·
To sum up an element is a pure substance made of atoms that always have the same number of protons.
总之,元素是由原子组成的纯物质,这些原子的质子数量总是相同的·
This means atoms with different numbers of protons are different elements.
这意味着具有不同数量质子的原子是不同的元素·
The number of protons in one atom of an element is called the atomic number.
一个元素的原子中质子的数量称为原子序数·
The number of protons plus neutrons in one atom is called the mass number.
一个原子中质子加中子的数量称为质量数·
Isotopes are atoms of the same element with different numbers of neutrons.
同位素是具有不同数量中子的同一元素的原子·
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