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化学基础之什么是同位素?

What Are Isotopes? | Chemistry Basics

Hey there folks
大家好
we’re excited to be launching a brand new series
我们很激动要推出一个新的系列
called Chemistry Basics.
叫基础化学
We figured it’s about time
我们觉得是时候
to get you the real nitty gritty on some serious chemistry topics
让你了解一些严肃的化学话题的本质了
like isotopes and radioactivity, the periodic table
比如同位素 放射性 元素周期表
the pH scale and a whole bunch of other fascinating stuff.
ph值等其他一大堆有趣的东西
When one of these topics comes up in a Reactions video
视频中每出现一个化学话题时
we’re gonna link directly to the Chemistry Basics video
会直接链接到相关基础化学的视频
so you can get that extra dose of chemical knowledge.
这样你能了解其他的化学知识
In the meantime, the videos will exist over here in a playlist.
同时 这些视频将储存在播放列表中
So here’s the first episode. We sure hope you love it.
这是第一集 我们真心希望你能喜欢
So you’ve heard about isotopes
你们都听说过同位素
but what exactly are they?
但它们到底是什么呢?
You probably know that atoms have a dense nucleus
你可能知道原子有一个密集的原子核
made up of positively charged protons and neutral neutrons
由带正电的质子和不带电的中子组成
and that the nucleus is surrounded by a bunch of negatively charged electrons.
而且它被一堆带负电荷的电子包围着
Isotopes are atoms of the same element
同位素就是质子数
meaning to have the same number of protons and electrons
和电子数相同的一类原子
but that that have different numbers of neutrons
但是有不同数目的中子
The differing numbers of neutrons give isotopes different masses.
这使得同位素的质量不同
Back in the early 1900’s,
早在20世纪初
the discoverer of the electron, J.J. Thomson
电子的发现者:约瑟夫·约翰·汤姆森
with the help of the student Francis W. Aston
在他的学生阿斯顿的帮助下
identified two different types of neon atoms.
发现了两种不同类型的氖原子
One type with 10 protons, 10 electrons, and 10 neutrons.
一种有10个质子 10个电子和10个中子
and then one with 10 protons, 10 electrons, and 12 neutrons
另一种有10个质子 10个电子和12个中子
.Aston went on to invent a groundbreaking machine
后来他发明了一种开创性的机器
that he called a mass spectrograph
称之为质谱仪
Using this machine
利用这台机器
Aston identified hundreds of other isotopes of other elements.
汤姆森发现了数百个其他的元素的同位素
The mass spectrometer is now used in labs all over the world
如今质谱仪应用于全世界所有的实验室
and Aston won the 1922 Nobel Prize in Chemistry for his work.
他的研究成果也获得了1922年的诺贝尔化学奖
These are the isotopes of neon that Thomson Aston saw
这是汤姆森看到的氖的同位素
The numbers you see here
你在这里看到的数字
tell you the total number of protons plus neutrons in each atom,
是这个原子质子和中子的总数
and they also tell you the isotope’s approximate mass.
它们也表示了这个原子的近似质量
Technically, the mass of an atom would include protons, neutrons, and electrons
准确地说 原子质量包括质子 中子和电子的质量
but since the mass of an electron
但由于电子的质量
is almost two thousand times less than that of protons and neutrons,
几乎是质子或中子的两千分之一
we can basically ignore them.
我们基本上可以忽略它们
When it comes to atoms and their behavior,
当谈到原子及其变化反应时
there’s an important distinction to make between chemical reactions and nuclear reactions
化学反应与核反应之间有一个重要的区别
Chemical reactivity is defined by the electrons that atoms possess.
化学反应是由原子所拥有的电子来决定的
When atoms come into contact with one another
当原子相互接触时
it’s their outer electrons that interact
其实是它们的外层电子相互作用
and determine the type and the intensity of the reaction
并决定了反应的类型和强度
Since isotopes of a given element have the same number of electrons
由于同位素有相同数量的电子
they will undergo similar reactions.
所以它们的化学反应类似
On the other hand, nuclear reactions rely on the particles in the nucleus.
另一方面 核反应依靠于原子中的粒子
so different isotopes will undergo different nuclear reactions.
所以不同的原子会有不同的核反应
because of the differences in the makeup of their nuclei
因为原子核的组成不同
So what happens in a nuclear reaction?
所以核反应发生了什么变化?
Basically something changes in the nucleus.
基本上是原子核发生了变化
Because the nucleus is made up of protons and neutrons,
因为原子核是由质子和中子组成的
you might think that all of those positive charges crammed together
你可能认为所有正电荷挤在一起
and repelling one another would make the nucleus unstable
相互排斥会导致原子核不稳定
Luckily there’s a force known as the Strong Nuclear Force
幸运的是 有一种力被称为强核力
that acts as the glue that holds the whole thing together.
它像胶水一样把整个原子核粘在一起
But when the nucleus of an atom contains lots of protons and neutrons
但是当原子核中含有大量质子和中子时
or when certain neutron to proton ratios exist
或当中子数与质子数存在一定比例时
even the Strong Nuclear Force can’t hold it all together
就连强大的核力也无法维持
and the whole thing can become unstable.
整个原子会变得不稳定
When that happens,
当这种情况发生时
the atom’s nucleus will either kick out some particles or rearrange itself,
原子核就会踢出一些粒子或者重新排列
Typically one of three things happens
通常有以下三种类型的衰变
Alpha Decay is when two neutrons and two protons are kicked out of the nucleus
α衰变指两个中子和两个质子被踢出原子核
to form two different species: a helium nucleus
然后形成两个不同种类的原子:氦原子
and a totally different element than the one we started with
和一个与之前完全不同的元素
In this case uranium ejects the alpha particle and becomes thorium.
比如铀衰变 会喷射出粒子并变成钍
In Beta Decay a neutron splits into a proton and an electron
在β衰变中 一个中子分裂成一个质子和一个电子
and the electron is ejected from the nucleus.
其中电子会被逐出原子核
Because this changes the number of protons in the nucleus
因为衰变改变了原子核中的质子数
a new element is formed
因此一个新元素诞生
In this case thorium becomes protactinium.
钍衰变会变成镤
Gamma Decay is when protons and neutrons in the nucleus
γ衰变是指原子核中的质子和中子
are rearranged to reduce the energy of an unstable atom
被重新排列以降低不稳定原子的能量
These rearrangements come with the release of energy in the form of gamma rays
原子重新排列时 会以伽马射线的方式释放能量
This time, since the number of protons in the nucleus stays the same
这次 由于原子核中的质子数保持不变
no new element is formed
所以没有新元素形成
These spontaneous changes in nuclei are known as radioactivity.
一些原子核自发的衰变被称为放射性
While radioactive substances can be hazardous,
虽然放射性物质可能是有害的
in some cases they can also be incredibly useful.
但在某些情况下 它们也可能非常有用
They give us an accurate way to tell how old things are,
比如准确判断古物的年龄
they can be used to detect leaks in pipes
还可以用来检测管道中的泄漏
or even see where certain medicines go in your body.
甚至看看某些药物在你体内的去向
Thanks for watching,
感谢收看
and make sure to check out the other videos in this series here.
请观看本系列的其他视频

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科普:什么是同位素?

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视频来源

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