Atom and nucleus

Atomism The idea that matter is made up of discrete units is a very old idea, appearing in many ancient cultures such as Greece and India. The word "atom" was coined by the ancient Greek philosophers Leucippus and his pupil Democritus.

Atom and nucleus

Radioactive decay If a nucleus has too few or too many neutrons it may be unstable, and will decay after some period of time.

For example, nitrogen atoms 7 protons, 9 neutrons beta decay to oxygen atoms 8 protons, 8 neutrons within a few seconds of being created. In this decay a neutron in the nitrogen nucleus is turned into a proton and an electron by the weak nuclear force.

The element of the atom changes because while it previously had seven protons which makes it nitrogen it now has eight which makes it oxygen. Many elements have multiple isotopes which are stable for weeks, years, or even billions of years.

Nuclear fusion When two light nuclei come into very close contact with each other it is possible for the strong force to fuse the two together.

It takes a great deal of energy to push the nuclei close enough together for the strong force to have an effect, so the process of nuclear fusion can only take place Atom and nucleus very high temperatures or high densities.

Once the nuclei are close enough together the strong force overcomes their electromagnetic repulsion and squishes them into a new nucleus. A very large amount of energy is released when light nuclei fuse together because the binding energy per nucleon increases with mass number up until nickel Stars like our sun are powered by the fusion of four protons into a helium nucleus, two positronsand two neutrinos.

The uncontrolled fusion of hydrogen into helium is known as thermonuclear runaway. Research to find an economically viable method of using energy from a controlled fusion reaction is currently being undertaken by various research establishments see JET and ITER.

Nuclear fission For nuclei heavier than nickel the binding energy per nucleon decreases with the mass number.

Atom - Wikipedia

It is therefore possible for energy to be released if a heavy nucleus breaks apart into two lighter ones. This splitting of atoms is known as nuclear fission.

The process of alpha decay may be thought of as a special type of spontaneous nuclear fission. This process produces a highly asymmetrical fission because the four particles which make up the alpha particle are especially tightly bound to each other, making production of this nucleus in fission particularly likely.

Atom and nucleus

For certain of the heaviest nuclei which produce neutrons on fission, and which also easily absorb neutrons to initiate fission, a self-igniting type of neutron-initiated fission can be obtained, in a so-called chain reaction.

The fission or "nuclear" chain-reaction, using fission-produced neutrons, is the source of energy for nuclear power plants and fission type nuclear bombs such as the two that the United States used against Hiroshima and Nagasaki at the end of World War II.

Heavy nuclei such as uranium and thorium may undergo spontaneous fissionbut they are much more likely to undergo decay by alpha decay. For a neutron-initiated chain-reaction to occur, there must be a critical mass of the element present in a certain space under certain conditions these conditions slow and conserve neutrons for the reactions.

There is one known example of a natural nuclear fission reactorwhich was active in two regions of OkloGabon, Africa, over 1.

Atomic nucleus - Wikipedia

However, it is not known if any of this results from fission chain-reactions. Production of heavy elements[ change change source ] As the Universe cooled after the big bang it eventually became possible for particles as we know them to exist. The most common particles created in the big bang which are still easily observable to us today were protons hydrogen and electrons in equal numbers.Apr 16,  · Just how small are atoms?

And what's inside them? The answers turn out to be astounding, even for those who think they know. This fast .

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Atomic nucleus. The central region of an atom. Atoms are composed of negatively charged electrons, positively charged protons, and electrically neutral neutrons. The protons and neutrons (collectively known as nucleons) are located in a small central region known as the nucleus.

The electrons move in orbits which are large in comparison with. The nucleus is very, very small and very, very dense when compared to the rest of the atom.

Not only is the nucleus very small, but it also contains most of the mass of the atom. In fact, for all practical purposes, the mass of the atom is the sum of the masses of the protons and neutrons.

The atomic nucleus is the central part of the atom. There is a lot to be told by the structure of the atomic nucleus. This lesson goes through the structure of the atomic nucleus and other factors.

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In chemical element: The structure of atoms within an atom, a small nucleus, which generally contains both protons and neutrons, is surrounded by a swarm, or cloud, of electrons.

The fundamental properties of these subatomic particles are their weight and electrical charge. The nucleus is very, very small and very, very dense when compared to the rest of the atom.

Not only is the nucleus very small, but it also contains most of the mass of the atom. In fact, for all practical purposes, the mass of the atom is the sum of the masses of the protons and neutrons.

What is an Atom? | Parts of an Atom