proton Protons are spin-½ fermions and are composed of three quarks, making them baryons. The two up quarks and one down quark of the proton are held together by the strong force, mediated by gluons. The proton has an approximately exponentially decaying positive charge distribution with a mean square radius of about 0.8 fm.


Protons and neutrons are both nucleons, which may be bound by the nuclear force into atomic nuclei. The nucleus of the most commonisotope of the hydrogen atom is a lone proton. The nuclei of the heavy hydrogen isotopes deuterium and tritium contain one proton bound to one and two neutrons, respectively. All other types of atoms are composed of two or more protons and various numbers of neutrons. The number of protons in the nucleus determines the chemical properties of the atom and thus which chemical element is represented; it is the number of both neutrons and protons in a nuclide which determine the particular isotope of an element.
external image Quark_structure_proton_svg.png

Electron The electron is a subatomic particle that carries a negative electric charge. It has no known components or substructure, and therefore is believed to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton. The intrinsicangular momentum (spin) of the electron is a half integer value in units of //ħ//, which means that it is a fermion. The antiparticle of the electron is called the positron, which is identical to the electron except that it carries electrical and other charges of the opposite sign. When an electron collides with a positron, they may either scatter off each other or be totally annihilated, producing a pair (or more) ofgamma ray photons. Electrons, which belong to the first generation of the lepton particle family, participate in gravitational,electromagnetic and weak interactions. Electrons, like all matter, have quantum mechanical properties of both a particle and a wave, so they can collide with other particles and be diffracted like light. However, this duality is best demonstrated in experiments with electrons, due to their tiny mass. Since an electron is a fermion, no two electrons can occupy the same quantum state, in accordance with the Pauli exclusion principle. external image electron_capture.jpg

taken from http://en.wikipedia.org/wiki/Electron


taken from:http://www.youtube.com/watch?v=geRNyjVkD4M




What are atoms made of?
Particles that are smaller than the atom are called subatomic particles. The three main subatomic particles that form an atom are protons, neutrons, and electrons. The center of the atom is called the nucleus.

Protons and Neutrons

Protons and neutrons make up the nucleus of an atom. All protons are identical to each other, and all neutrons are identical to each other. Protons have a positive electrical charge, so they are often represented with the mark of a "+" sign. Neutrons have no electrical charge and are said to help hold the protons together (protons are positively charged particles and should repel each other).

If all protons are identical and all neutrons are identical, then what makes the atoms of two different elements different from each other? For example, what makes a hydrogen atom different from a helium atom? The number of protons and neutrons in the nucleus give the atoms their specific characteristics. In the graphic below you will notice that each of the three elements have different numbers of protons and neutrons. They would also like to have the same number of electrons as they have protons in order to stay electrically balanced.


external image Atom.jpg
Electrons
Circling around outside the nucleus are tiny little particles called electrons. Electrons have a negative charge. Electrons spin as they circle the nucleus billions of times every second. They are moving so fast and the path that they travel is not the same each time, so that if we could see these electrons, they might appear to look like a cloud around the nucleus.
According to current theory, electrons are arranged in energy levels around the nucleus. When electrons gain or lose energy, they jump between energy levels as they are rotating around the nucleus. For example, as electrons gain energy, they might move from the second to the third level. Then, as they lose energy, they might move back to the second level or even to the first energy level. Only a certain number of electrons can be in an energy level at the same time.
















subatomic particles
In physics, subatomic particles are the particles composing nucleons and atoms. There are two types of subatomic particles: elementary particles, which are not made of other particles, and composite particles. Particle physics and nuclear physics study these particles and how they interact.
Elementary particles of the Standard Model include:


  • Six "flavours" of quarks: up, down, bottom, top, strange, and charm;
  • Six types of leptons:electron, electron neutrino, muon, muon neutrino, tauon, tauon neutrino;
  • Twelve gauge bosons (force carriers): the photon of electromagnetism, the three W and Z bosons of the weak force, and the eight gluons of the strong force.
Composite subatomic particles (such as protons or atomic nuclei) are bound states of two or more elementary particles. For example, a proton is made of two up quarksand one down quark, while the atomic nucleus of helium-4 is composed of two protons and two neutrons. Composite particles include all hadrons, a group composed of baryons (e.g., protons and neutrons) and mesons (e.g., pions and kaons).
There are hundreds of known subatomic particles. Most are either the result of cosmic rays interacting with matter, or have been produced by scattering processes in particle accelerators.
taken of http://en.wikipedia.org/wiki/Subatomic_particle

nucleus
All the bound protons and neutrons in an atom make up a tiny atomic nucleus, and are collectively called nucleons. The radius of a nucleus is approximately equal to an a mathematic operation fm, where A is the total number of nucleons. This is much smaller than the radius of the atom, which is on the order of 105 fm. The nucleons are bound together by a short-ranged attractive potential called the residual strong force. At distances smaller than 2.5 fm this force is much more powerful than the electrostatic force that causes positively charged protons to repel each other.
Atoms of the same element have the same number of protons, called the atomic number. Within a single element, the number of neutrons may vary, determining the isotope of that element. The total number of protons and neutrons determine the nuclide. The number of neutrons relative to the protons determines the stability of the nucleus, with certain isotopes undergoing radioactive decay.
The neutron and the proton are different types of fermions. The Pauli exclusion principle is a quantum mechanical effect that prohibits identical fermions, such as multiple protons, from occupying the same quantum physical state at the same time. Thus every proton in the nucleus must occupy a different state, with its own energy level, and the same rule applies to all of the neutrons. This prohibition does not apply to a proton and neutron occupying the same quantum state.
For atoms with low atomic numbers, a nucleus that has a different number of protons than neutrons can potentially drop to a lower energy state through a radioactive decay that causes the number of protons and neutrons to more closely match. As a result, atoms with roughly matching numbers of protons and neutrons are more stable against decay. However, with increasing atomic number, the mutual repulsion of the protons requires an increasing proportion of neutrons to maintain the stability of the nucleus, which modifies this trend. Thus, there are no stable nuclei with equal proton and neutron numbers above atomic number Z = 20 (calcium); and as Z increases toward the heaviest nuclei, the ratio of neutrons per proton required for stability increases to about 1.5.

The number of protons and neutrons in the atomic nucleus can be modified, although this can require very high energies because of the strong force. Nuclear fusion occurs when multiple atomic particles join to form a heavier nucleus, such as through the energetic collision of two nuclei. For example, at the core of the Sun protons require energies of 3–10 keV to overcome their mutual repulsion—the coulomb barrier and fuse together into a single nucleus. Nuclear fission is the opposite process, causing a nucleus to split into two smaller nuclei—usually through radioactive decay. The nucleus can also be modified through bombardment by high energy subatomic particles or photons. If this modifies the number of protons in a nucleus, the atom changes to a different chemical element.





external image a4atom.jpg


taken from: http://en.wikipedia.org/wiki/Atom#Nucleus




The Construction of Atom Models: Eliminative Inductivism and its Relation to Falsificationism


Falsificationism has dominated 20th century philosophy of science. It seemed to have eclipsed all forms of inductivism. Yet recent debates have revived a specific form of eliminative inductivism, the basic ideas of which go back to F. Bacon and J.S. Mill. These modern endorsements of eliminative inductivism claim to show that progressive problem solving is possible using induction, rather than falsification as a method of justification. But this common ground between falsificationism and eliminative inductivism has not led to a detailed investigation into the relationship, if any, which may exist between these two methodologies. This paper reviews several versions of eliminative inductivism, establishes a natural relation between eliminative inductivism and falsificationism, which derives from the distinction between models and theories, and carries out this investigation against a case study of the construction of atom models. The result of the investigation is that falsificationism is a form of eliminative inductivism in the limit of certain constraints.
atom models - scientific constraints - enumerative inductivism - three versions of eliminative inductivism - models and theories - falsificationism
external image atom0.jpgFE06721B-B5C3-4DA3-9D5DDCF34F64CD5F.jpgLarge.jpg

taken from:http://www.springerlink.com/content/p267411544376010/


​the constitution of the atom: ​

Modern science holds that matter is not infinitely divisible, that there is an ultimate particle of every substance. If this particle is broken up that particular form of matter will be destroyed. This particle is the molecule. It is composed of another division of matter called the atom. Generally, probably always, a molecule consists of several atoms. The atoms unite to form molecules and cannot exist except as constituents of molecules. If a molecule of any substance were broken up, the substance would cease to exist and its constituent atoms would go to form or to enter into some other molecule or molecules. There is a tendency to consider the molecule of modern science as identical with the atom of the old philosophers but the modern atomic theory has given the molecule a different status from that of the old-time atom. Atom, as used in natural science, has a specific meaning based upon the theory of chemistry. This meaning is modified by recent work in the field of radioactivity, but the following will serve as a definition. It is the smallest particle of an element which can exist in a compound. An atom cannot exist alone as such. Atoms combine with each other to form molecules. The molecule is the smallest particle of matter which can exist without losing its distinctive properties. It corresponds pretty closely to the old Epicureanatom. The modern atom is an entirely new conception. Chemistry teaches that the thousands of forms of matter upon the earth, almost infinite in variety, can be resolved into eighty substances, unalterable by chemical processes and possessing definite spectra. These, substances are called elements. The metals, iron, gold, silver and others, sulphur, and carbon are familiar example of elements. A mass of an element is made up of a collection of molecules. Each molecule of an element as a rule is composed of two atoms. Elements combine to form compound substances of various numbers of atoms in the molecule. Water is an example of a compound substance, or chemical compound. Its molecule contains three atoms, two atoms of hydrogen, and one atom of oxygen. If a quantity of these two elements were mixed, the result would be a mechanical mixture of the molecules of the two. But if heat, or some other adequate cause were made to act, chemical action would follow and the molecules, splitting up, would combine atom with atom. Part of a molecule of oxygen--one atom--would combine with part of two atoms of hydrogen--two atoms. The result would be the production of a quantity of molecules of water. Each water molecule contains one atom of oxygen and two atoms of hydrogen. The splitting-up of the elemental molecules into atoms is synchronous with their combining into molecules, so that an atom never exists alone. The molecules of the elements, oxygen and hydrogen, have disappeared, and in their places are molecules of water. There are about eighty kinds of atoms known, one kind for each element, and out of these the material world is made.

external image atomo.gif
taken from:http://www.newadvent.org/cathen/02051c.htm