You probably know that all stuff is made up of atoms and that an atom is a really, really, really, really tiny particle. Every atom has a core, which is made up of at least one positively charged particle called a proton, and in most cases, some number of neutral particles called neutrons. That core is surrounded by negatively charged particles called electrons. The identity of an atom is determined only by the number of protons in its nucleus. Hydrogen is hydrogen because it has just one proton, carbon is carbon because it has six, gold is gold because it has 79, and so on. Indulge me in a momentary tangent. How do we know about atomic structure? We can't see protons, neutrons, or electrons. So, we do a bunch of experiments and develop a model for what we think is there. Then we do some more experiments and see if they agree with the model. If they do, great. If they don't, it might be time for a new model. We've had lots of very different models for atoms since Democritus in 400 BC, and there will almost certainly be many more to come. Okay, tangent over. The cores of atoms tend to stick together, but electrons are free to move, and this is why chemists love electrons. If we could marry them, we probably would. But electrons are weird. They appear to behave either as particles, like little baseballs, or as waves, like water waves, depending on the experiment that we perform. One of the weirdest things about electrons is that we can't exactly say where they are. It's not that we don't have the equipment, it's that this uncertainty is part of our model of the electron. So, we can't pinpoint them, fine. But we can say there's a certain probability of finding an electron in a given space around the nucleus. And that means that we can ask the following question: If we drew a shape around the nucleus such that we would be 95% sure of finding a given electron within that shape, what would it look like? Here are a few of these shapes. Chemists call them orbitals, and what each one looks like depends on, among other things, how much energy it has. The more energy an orbital has, the farther most of its density is from the nucleus. By they way, why did we pick 95% and not 100%? Well, that's another quirk of our model of the electron. Past a certain distance from the nucleus, the probability of finding an electron starts to decrease more or less exponentially, which means that while it will approach zero, it'll never actually hit zero. So, in every atom, there is some small, but non-zero, probability that for a very, very short period of time, one of its electrons is at the other end of the known universe. But mostly electrons stay close to their nucleus as clouds of negative charged density that shift and move with time. How electrons from one atom interact with electrons from another determines almost everything. Atoms can give up their electrons, surrendering them to other atoms, or they can share electrons. And the dynamics of this social network are what make chemistry interesting. From plain old rocks to the beautiful complexity of life, the nature of everything we see, hear, smell, taste, touch, and even feel is determined at the atomic level.
你或許知道所有的物質皆由原子組成, 而原子 真的非常、非常、非常的微小。 每一個原子都有一個原子核, 由至少一個帶正電的粒子組成, 這種正電粒子叫做質子, 在大多數情況下, 核內還有一些中性粒子稱為中子。 原子核被稱為帶負電的電子包圍。 一個原子的特性 僅由原子核中質子的數量來決定。 核內只有一個質子的就是氫, 有6個質子就是碳, 金原子核則擁有79個質子, 諸如此類的還有很多。 請容我講些題外話: 我們如何得知道原子的結構呢? 質子、中子或電子都是 肉眼看不見的東西。 所以,我們先進行許多實驗, 然後建構出我們認為合宜的原子模型, 然後再進行更多的實驗, 來看看實際情況是否符合模型。 如果是的話最好。 如果不是, 那就再建立一個新模型。 自西元前400年的德謨克利特以來, 我們曾有過不同的原子模型, 而且將來肯定會有更多的模型出現。 好了,言歸正傳。 原子核的粒子總是緊緊粘在一起, 但電子卻可以自由移動, 這就是化學家熱愛電子的原因。 如果我們可以和它們結婚, 我們真的會這樣做。 但是電子很奇怪, 它們的表現既像是粒子, 像是棒球, 也像是波,水一般的波浪。 在不同的實驗中表現出相異的特性。 關於電子最詭異的事情是, 我們無法確認它們的所在位置。 這並不是說我們沒有適當的設備, 而是這種不確定性 就是電子模型的一部分特性。 所以,好吧!我們不能精確定位它們, 但我們可以說, 在原子核周圍的某一特定區域中, 找到一個電子的機率是多少。 這就表示我們能提出以下的問題: 如果我們繞原子核畫一個形狀, 使得我們有95%的把握, 在這個形狀中找到一個特定的電子, 它會是什麼樣的形狀呢? 這裡有幾個形狀, 化學家們稱之為軌域。 決定每個軌域形狀的因素之一 是它們所擁有的能量。 軌域的能量越高, 其主要部分就離原子核越遠。 順便提一下, 為什麼我們說95% 而不是100%的把握呢? 好吧,這是我們電子模型 另一個比較奇特的地方, 從距離原子核一定距離開始, 發現電子的機率 就開始隨著距離增加而下降, 差不多呈現指數衰減, 這代表機率會越來越接近零, 但事實上永遠不會達到零。 所以,每一個原子中, 總有一些很小,但是不為零的可能性, 於很短很短的時段中, 可能其中有一個電子 正位於宇宙的另一端。 但是絕大部分時間, 電子都距離原子核很近, 呈現出帶負電的電子雲, 電子雲會隨著時間改變位置。 一個原子的電子如何與 另一個原子的電子發生互相作用, 幾乎決定了一切化學反應的性質。 原子可以放棄自己的電子, 把它們給其他原子, 或者與其他原子共用電子。 而這個社交網路的動態 使化學變得很有趣。 從普通的舊石頭 到美好而複雜的生命, 自然界我們一切見到、 聽到、聞到、 品嘗到、觸摸到, 甚至是能感覺到的,