There is actually ambiguity here as to whether iron is the most stable metal, and there are many types of stability. The reason why iron is the most stable lies in its binding energy, which is a problem at the atomic nucleus level. The comparison between iron gold, and silver is actually at the level of chemical reactions. The essence of this level is the difference in chemical properties caused by the arrangement of electrons outside the nucleus. The stability of gold and silver comes from this. So, the two are also very different.
Iron is the sixth most abundant element in the universe, and there's a reason why it is. This is because iron is the end point of many stars. Iron is actually the hurdle that many stars cannot overcome. Why do you say that? Why do stars have a relationship with iron?
This actually starts with the characteristics of stars. If I have to sum up the relationship between stars and elements in one sentence, it must be: stars are the alchemy furnaces of elements. In the universe, hydrogen atoms account for more than 70% of the total elements; most of the rest are helium, and less than 1% are other elements. (This is about known matter, without dark matter and dark energy)
If you look carefully at the periodic table of elements, hydrogen and helium are the first two, with the fewest protons. The hydrogen nucleus can be said to be a proton.
In fact, this has something to do with the burning of stars. The burning of stars relies on nuclear fusion reactions, similar to hydrogen bombs.
Nuclear fusion reactions are actually different from ordinary chemical reactions. You can also understand them as being different from ordinary explosions. Normal explosions occur at the atomic level. Nuclear fusion occurs at the level of atomic nuclei.
Therefore, the burning of stars is the aggregation of atomic nuclei. There are two main ways: one is called: proton-proton reaction.
Another type is called the carbon-nitrogen-oxygen cycle, which is actually the polymerization of hydrogen into helium-4, that is, the polymerization of four hydrogen nuclei into one helium-helium, releasing a large amount of energy. In the process of carbon, nitrogen, and oxygen cycle, carbon, nitrogen, and oxygen only play a catalytic role.
Therefore, stars burn hydrogen atoms. When the hydrogen atoms are burned out, a bunch of nitrogen atoms will remain. Then, under the action of gravity, they will continue to aggregate elements higher in the periodic table. Stars with different masses will Stay in different places, and the vast majority end up stuck in front of iron atoms.
The reason for this is that a large amount of energy is required to make iron undergo nuclear fusion reaction, and the energy produced by iron after nuclear fusion is less than the energy required for nuclear fusion reaction. To put it bluntly, it means making ends meet. The binding energy of iron is also relatively large. Only stars with a certain mass can fuse iron and produce supernova explosions under the influence of super-strong gravity.
Therefore, iron is very stable, and it is stable here, at the nuclear level.
Let's take gold as an example here. Compared with iron and gold, some people will definitely think that gold is more stable. In fact, more stable here means that the chemical properties are more stable; that is, chemical reactions are less likely to occur. Chemical reactions generally refer to the breaking and forming of chemical bonds. Chemical reactions do not change the nucleus but only interact with the electron cloud outside the nucleus, so nuclear reactions have nothing to do with chemical reactions; that is, they have nothing to do with the stability of iron we mentioned above.
So, in terms of chemical properties, why are gold atoms more stable than iron atoms?
This is mainly related to gold's high atomic number, which makes it not only subject to the constraints of quantum mechanics but also reflects the correspondence of the theory of relativity.
To understand this problem, we can start from chemistry in middle and high school. We all know that there are many electrons around atoms, and they are arranged in layers according to their energy levels, which are restricted by the Pauli exclusion principle. The outermost electrons determine most of the atom's physical and chemical properties.
The gold atom we are talking about here has six layers of electrons outside the nucleus. The innermost layer of electrons has extremely high energy and flies at 65% of the speed of light. At this time, the effects of relativity cannot be ignored. The electrons will become heavier and their orbits will shrink, so the orbits of the outermost electrons will also shrink. This means that for gold to undergo a chemical reaction, it must have not only the outermost electrons but also the sub-outer electrons. To lose these electrons, a large amount of energy needs to be absorbed. This makes gold atoms particularly stable.
For this reason, gold always exists in the form of simple substances most of the time and rarely undergoes chemical reactions.
On the other hand, the iron atom has an atomic number of 26. It does not have chemical properties like gold. Iron can easily react with oxygen and water. Free iron can basically only be found in meteorites. On Earth, iron generally exists in the form of compounds, that is, various iron ores.
Finally, the stability of iron is actually reflected in its resistance to nuclear fusion reactions. The stability of gold than iron is mainly reflected in the chemical properties, which are determined by the electron configuration outside the nucleus.
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