Nuclear energy
Nuclear energy is transferred when there are changes to the nucleus of the atom: fission and fusion processes
It is not easy to carry out these changes, which liberate large amounts of energy.
The atom consists of electrons orbiting the nucleus. When you form molecules, the atoms get together, by forming chemical bonds. In this process only the electrons are involved, so that the nucleus stands by. These are chemical processes. The energy transferred corresponds to the energies of the electrons involved.
Nuclear processes involve changes in the nucleus. Because the nucleons (protons and neutrons) are subjected to enormous forces (much stronger than the forces electrons are subjected to) the energies involved are higher in nuclear processes than in chemical processes.
There are two major types of nuclear reactions:
Nuclear fission and nuclear fusion.
In nuclear fission, an atomic nucleus is split.
It is usually the uranium atom that is employed for this purpose, because it is the largest atom in the periodic table and as a result it is a bit unstable. But it still needs to be hit in order to split.
The uranium atom can be split when it is hit by a neutron. This way, it produces 2 or 3 fragments, and 2 or 3 more neutrons, which will hit other nuclei and split them. This way the process follows through and a chain reaction is sustained.
The nuclear fuel (uranium) can transfer its energy in a fraction of a second (atomic bomb) or it can be consumed throughout a larger period, of one year or more (nuclear reactor for producing electricity).
In nuclear fusion, nuclei are fused together
This is usually achieved using hydrogen atoms to produce helium. The nuclei of atoms are positively charged, so that they will repel strongly at short distances from each other, what makes their fusion difficult to accomplish. Very high temperatures must be used for this purpose, temperatures as high as in the center of the Sun (about 300 million degrees celsius).
Hydrogen has atomic number Z=1. If two of them fuse together an element with Z=2 will be produced : helium.
You can carry on fusing elements and producing heavier ones, but that is even more difficult to achieve. However this occur inside stars and that is how all the elements we see on our planet and in the Universe have been produced. We are made of stardust!
Fusion reactions take place inside the Sun and all the stars. Man made fusion reactions are produced in the hydrogen bomb. There has been a lot of research to produce a nuclear reactor to sustain fusion reactions in a controlled manner, but that goal has not yet been achieved.
Advantages and disadvantages of nuclear power
When we say nuclear power we refer to nuclear reactors that ar based on the fission of uranium or plutonium.
The main advantage of nuclear power is the fact that it doesn't produce gaseous emissions like CO2 , a gas that causes global warming, or SO2, a gas that causes acid rain.
That doesn't mean that it is a clean energy. In fact, nuclear reactors produce lots of usuless radioactive elements that are a huge threat for life and also for the environment. These are collectively known as nuclear waste. It is very dangerous to handle and the problem of where to put it is still open.
Energetics of nuclear reactions:
In nuclear reactions mass is transformed into energy. Products have lower masses than the reactants, and that difference equates to the amount of energy transferred in the reaction, according to Einstein's famous equation (shown on the top left side of the page).
That differs from what happens in chemical reactions, where the masses are always conserved.
Also, because the nuclear forces are much stronger than the electrical forces involved in chemical bonding, nuclear reactions can release much more energy than a chemical reaction. That is why a nuclear explosion can be millions of times as strong as a reaction involving TNT. In fact, the energy release of a hydrogen bomb is measured in megatons, which means that it is equivalent to exploding millions of tons of TNT.