Which of the particles in an atom is fundamental?
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The most fundamental particles known to exist at the moment are quarks and leptons. Quarks are the things the make up the pieces of the nucleus in an atom and leptons include things like electrons.\n\nWithin a nucleus you will have heard of Protons and Neutrons ro collectively Nucleons. Well a quark is a sub unit of one of these so called "Nucleons". There are three quarks to every nucleon. There are many types of quark and these create many types of particles, most of which are extremely shortlived. You can learn more about the world of Particle Physics in the Particle Physics Adventure.\n\nhttp://particleadventure.org/particleadventure/
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ATOM..basic building block\n \n[Gr.,=uncuttable (indivisible)], basic unit of matter; more properly, the smallest unit of a chemical element having the properties of that element.  That is the definition.  Continue to read further; it really gives great detail!!!!!\n\nStructure of the Atom\n\nThe atom consists of a central, positively charged core, the nucleus, and negatively charged particles called electrons that are found in orbits around the nucleus.\n\nThe Nucleus\n\nAlmost the entire mass of the atom is concentrated in the nucleus, which occupies only a tiny fraction of the atom's volume. The nucleus of an atom consists of neutrons and protons, the neutron being an uncharged particle and the proton a positively charged one. Their masses are almost equal. Atoms containing the same number of protons but different numbers of neutrons represent different forms, or isotopes, of the same element.\n\nThe Electrons\n\nSurrounding the nucleus of an atom are its electrons; for a neutral atom, the number of electrons is equal to the atomic number. The outermost electrons of an atom determine its chemical and electrical properties. An atom may combine chemically with another atom in various ways, either by giving up or receiving electrons, thus setting up an electrical attraction between the atoms (see ion), or by sharing one or more pairs of electrons (see chemical bond). Because metals have few outermost electrons and tend to give them up easily, they are good conductors of electricity or heat (see conduction).\n\nThe electrons are often described as revolving about the nucleus as the planets revolve about the sun. This picture, however, is misleading. The quantum theory has shown that all particles in motion also have certain wave properties. For a particle the size of an electron, these properties are of considerable importance. As a result the electrons in an atom cannot be pictured as localized in space, but rather should be viewed as smeared out over the entire orbit so that they form a cloud of charge. The electron clouds around the nucleus represent regions in which the electrons are most likely to be found. The shapes of these clouds can be very complex, in marked contrast to the simple elliptical orbits of planets. Surprisingly, the sizes of all atoms are comparable, in spite of the large differences in the number of electrons they contain.\n\nAtomic Weight and Number\n\nThe atomic number of an atom is simply the number of protons in its nucleus. The atomic weight of an atom is given in most cases by the mass number of the atom, equal to the total number of protons and neutrons combined. An atom may be conveniently symbolized by its chemical symbol with the atomic number and mass number written as subscript and superscript, respectively. For example, the symbol for uranium is U (atomic number 92); the isotopes of uranium with atomic weights 235 and 238 are indicated by 23592U and 23892U.\n\nDevelopment of Atomic Theory\n\nEarly Atomic Theory\n\nThe atomic theory, which holds that matter is composed of tiny, indivisible particles in constant motion, was proposed in the 5th cent. by the Greek philosophers Leucippus and Democritus and was adopted by the Roman Lucretius. However, Aristotle did not accept the theory, and it was ignored for many centuries. Interest in the atomic theory was revived during the 18th cent. following work on the nature and behavior of gases (see gas laws).\n\nFrom Dalton to the Periodic Table\n\nModern atomic theory begins with the work of John Dalton, published in 1808. He held that all the atoms of an element are of exactly the same size and weight (see atomic weight) and are in these two respects unlike the atoms of any other element. He stated that atoms of the elements unite chemically in simple numerical ratios to form compounds. The best evidence for his theory was the experimentally verified law of simple multiple proportions, which gives a relation between the weights of two elements th
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In biology?  Wow!  I would expect this in another category.  Atoms are the smallest particle into which an element can be divided.\n\nfor more information, see the site listed below:
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Protons and neutrons.
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Charge is a fundamental property. This means that we simply accept charge as an attribute of the particles. Much like we accept a person's name.\n\nIn other words, we don't know what causes charge in the sense which you inquire to know, but it doesn't prevent us from working with the particles.\n\nCharge aside, electrons and protons are very different particles. Electrons orbit atoms and weight next to nothing, while protons are locked in the nucleus of the atom and are considerably more massive.
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The definations wanted by you are given below-\n\nIn physics, matter is commonly defined as the substance of which physical objects are composed, not counting the contribution of various energy or force-fields, which are not usually considered to be matter per se (though they may contribute to the mass of objects). Matter constitutes much of the observable universe, although again, light is not ordinarily considered matter. Unfortunately, for scientific purposes, "matter" is somewhat loosely defined.\n\nMass is a property of a physical object that quantifies the amount of matter and energy it is equivalent to. Mass is a central concept of classical mechanics and related subjects, and there are several forms of mass within the framework of relativistic kinematics (see mass in special relativity and mass in General Relativity). In the theory of relativity, the quantity invariant mass, which in concept is close to the classical idea of mass, does not vary between single observers in different reference frames.\n\nAn elementary particle is a particle with no measurable internal structure, that is, it is not a composite of other particles. They are the fundamental objects of quantum field theory. Elementary particles can be classified according to their spin, with fermions having half-integer spin and bosons integer spin.\n\nSpace has been an interest for philosophers and scientists for much of human history. The term is used somewhat differently in different fields of study, hence it is difficult to provide an uncontroversial and clear definition outside of specific defined contexts. Disagreement also exists on whether space itself can be measured or is part of the measuring system. (See Space in philosophy.) Many fields use an operational definition in which the units of measurement are defined, but not space itself.\n\nIn chemistry and physics, an atom (Greek  átomos meaning "indivisible") is the smallest particle of a chemical element that retains its chemical properties. \n\nA chemical element, often called simply an element, is a substance that cannot be decomposed or transformed into other chemical substances by ordinary chemical processes. All matter consists of these elements and as of 2006, 117 unique elements have been discovered or artificially created. The smallest particle of such an element is an atom, which consists of electrons centered about a nucleus of protons and neutrons.\n\nIn chemistry, a molecule is an aggregate of two or more atoms in a definite arrangement held together by chemical bonds. Chemical substances are not infinitely divisible into smaller fractions of the same substance: a molecule is generally considered the smallest particle of a pure substance that still retains its composition and chemical properties. Certain pure substances (e.g., metals, molten salts, crystals, etc.) are best understood as being composed of networks or aggregates of atoms or ions instead of molecular units.\n\nIn particle physics, antimatter extends the concept of the antiparticle to matter, wherein if a particle and its antiparticle come into contact with each other, the two annihilate —that is, they may both be converted into other particles with equal energy in accordance with Einstein's equation E = mc2. This gives rise to high-energy photons (gamma rays) or other particle–antiparticle pairs-.
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Quantum Physics is the Science and Study of Atomic Particles, the most basic of which is the Electron, the Proton and the Neutron, and the futher study of the constituent parts of those particles, Quarks, Muons, Gluons, etc etc etc.\n\nThe Standard Model is the best way to learn these particles. There is (apparently) no rhyme or reason as to the why's and wherefor's of the Standard Model - meaning that nobody knows WHY the weights are what they are, nobody knows why the numbers shake out the way they do and the particles organize themselves the way they do - this is one of the last great mysteries of Physics that modern M-Theory (String or SuperString Theory) is attempting to answer.\n\nHere's a good link or three\n\nOf them all, I would recommend the Wiki as a great place to start... Take notes, it's fairly complex, you can do it!
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Atoms have a nucleus ( composed of protons and neutrons) and a cloud of electrons. The number of the different components varies between different elements.\n\nElectrons can only have specific energy levels in an atom - that is the energy is not continious but quantized. This is different from, say, the solar system, because a planet could theoretically be in any orbit. But we know from quantum mechanics (and many, many experiments) that electons can only occupy certain "orbits."\n\nSometimes an electron can be bumped into a higher orbit (the higher orbits have less energy, because they are not as tightly bound) or kicked out of the atom altogether. If a second electron moves into the spot it will release energy as it falls into that level.\n\nHydrogen is the easiest element to study. The nucleus is a single proton, and it can have only one electron. The different energy levels can be illustrated like this:\nhttp://hyperphysics.phy-astr.gsu.edu/hbase/hyde.html#c2\n(though in reality electrons don't travel on nice orbits)\n\nIf an electron in the second lowest level does a "quantum leap" to the very lowest, it will emit energy - light - at a very specific frequency. In this case 656 nanometers, which is red. If, on the other hand, an electron falls from the 3rd level down to the 1st level the emitted light is blue.\n\nA "spectrum" will show all of these distinct levels, with the brighter ones being the most common. This shows the spectrum of hydrogen with a diagram of the quantum leaps:\nhttp://hyperphysics.phy-astr.gsu.edu/hbase/hyde.html#c4\n\nIn other atoms it becomes more complex, not every jump is allowed, and in the precense of a magnetic field a "fine structure" is seen in the spectrum, as some of the main lines look double.\n\nThe result of all of this is that each different atom will give a different characteristic spectrum. So, you can use this to identify different elements in anything from crime scene samples to distant galaxies.
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The number of protons is equal to the number of electrons (unless it is an ion), but in this case they are equal. The atomic number is equal to the number of protons, and the mass number is the number of protons plus the number of neutrons.
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Quarks are fundamental subatomic particles. Your and my school physics probably stopped at electrons protons and neutrons, but leptons and quarks are now widely regarded as "more fundamental" i.e. the building blocks out of which protons and electrons and neutrons (known collectively as hadrons) are built.\n\nAs you might expect if there is a top quark, there is a bottom quark, too. In fact there are six types of quark in all. With various properties ...\n\nEach quark is assigned a baryon number, B  =  1/3, and a vanishing lepton number L  =  0. They have fractional electric charge, Q, either Q  =  +2/3 or Q  =  −1/3. The former are called up-type quarks, the latter, down-type quarks. \n\nEach quark is assigned a weak isospin: Tz  =  +1/2 for an up-type quark and Tz  =  −1/2 for a down-type quark. Each doublet of weak isospin defines a generation of quarks. There are three generations, and hence six flavours of quarks — the up-type quark flavours are up, charm and top; the down-type quark flavours are down, strange, and bottom (each list is in the order of increasing mass).\n\nThe fractional electric charges are worth a comment.\n\nAs you know electrons have a charge of -1 and protons a charge of + 1. This means that electrons contain three quarks with Q = -1/3 and protons contain three quarks, two of them having Q = +2/3 and one of them having Q - -1/3. And neutrons (charge 0) contain 3 quarks, one of them having Q = +2/3, and two of them having Q = -1/3\n\nQuarks are not seen in isolation as separate entities, they are contained within (or "confined" to) the hadrons of which they are part.
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Atom  \n\nThe smallest unit matter can be divided into whilst still retaining its chemical identity. Atoms are not single particles but complex arrangements of three types of particles. The subatomic particles, protons, neutrons and electrons, combine to form atoms. The protons and neutrons provide the bulk of an atom's mass and are concentrated into a tiny central region known as the atomic nucleus. The nucleus is held together by the strong nuclear force which acts between the constituent particles (termed nucleons ). The protons are positively charged and so mutually repel each other, but it is not until there are many of them that they overcome the nuclear force. Thus there is only one stable element beyond lead (Z=82). Whilst the radius of an atom is in the region of 10-10 metres, the atomic nucleus is about ten thousand times smaller at 10-14 metres. The volume surrounding the nucleus is where the electrons exist. They are much lighter than the protons and neutrons and carry a negative electrical charge. Being opposite in charge to the nucleus, the electrons are held in orbits around it by the force of electromagnetism. The electrons exist in electron orbitals around the nucleus. These orbitals are grouped into shells. Within each shell are energy levels which allow the electrons to exist in unique quantum states, depending upon their angular momentum (hence energy), in accordance with Pauli's exclusion principle . In a neutral atom the number of electrons equals the number of protons. When ionisation occurs, one or more electrons are provided with enough energy to escape the atom altogether. What remains is known as an ion because it is now positively charged and will behave in a different way chemically from neutral atom. The number of protons in the nucleus of an atom (the atomic number , Z) defines which chemical element it is. There are just over 110 known chemical elements and these can be arranged in a classification sequence known as the periodic table. The number of neutrons in any given atomic nucleus can also vary. The total number of protons + neutrons is termed the atomic mass number (A). Most atoms have a prefered number of neutrons at which their nuclei are stable. Atoms with more or less neutrons than the stable configuration are known as isotopes and will often undergo radioactive decay. The simplest of all atoms is hydrogen and is a special case which has a nucleus of one solitary proton and a single electron in orbit around it. It is the only nuclide (species of nucleus) with no neutron. A stable isotope of hydrogen is called deuterium which has one neutron in its nucleus; tritium is an unstable (radioactive) isotope of hydrogen and has two neutrons. See also atomic absorption , atomic emission , atomic number , molecule .
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zero to infinity.\n\nYou see hadrons (a kind of tiny particle smaller than an atom) have properties of both a solid particle, and a wave.\n\nA single quark can't really exist in nature (as far as scientists think for now), but anyway all particles have a wavefunction. Even your body has a wavefunction which is the sum of all the particles in your body.\n\nA probability wavefunction gives you an idea of how much time a thing is likely to be hanging around in a particular area.\n\nImagine a map of the word and you stick a red pin for every month you have been in a particular place. What would your wavefunction look like?\n\nA quark will have a wavefunction which is thickest (most red pins) near its locations inside a proton -- but it will also have some theoretically mathematically small probability of being on the other side of the moon for instance.\n\nThe wavefunction depends on mass, so we could just compare the electron mass to the quark mass -- but there is a fly in  the ointment. Quarks don't really have a real mass. They have various types of theoretical masses, but really they are measured by kooky-sounding properties like flavor, charm and color! Wacko huh? So there is no direct way to compare wavefunction/size to an electron.\n\nSo the answer is, it depends! zero to infinity.
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the simplistic answer involves the electrons, protons and neutrons. the more complex answer contains up quarks, down quarks- which are the building blocks of protons and neutrons. \nThen if we think about it we have also got anti-matter, which is involved in bonding and so forth, and so must be around somewhere. positrons, anti-bonding orbitals, etc.
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ATOM: Each atom consists of a central core with negatively charged electrons revolving around the core. The core consists of positively charged protons and uncharged neutrons. The core is called the nucleus of an atom. An atom as such is electrically neutral. Atoms of different elements have different and unique characteristics. Although all atoms are made up of protons, neutrons and electrons, it is the way these subatomic particles are arranged that gives each of the atom its unique characteristics.   \n\nATOMIC NUCLEUS: The nucleus of an atom is the very dense region in its centre consisting of protons and neutrons. The size of the nucleus is much smaller than the size of the atom itself, and almost all of the mass in an atom is made up from the protons and neutrons with almost no contribution from the electrons.  The nucleus of an atom consists of very tightly bound protons and neutrons which are further composed of sub-atomic fundamental particles known as quarks.
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Protons and neutrons build a nucleus.\nThe number of protons determines the kind of element.\nThe number of protons and neutrons determines the mass of an atom. The electrons outside the nucleus hardly contribute to the mass.\nThe number of protons equals the number of electrons. That is why an atom is electrically neutral.
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To explain many chemical process it is necessary to assume charged particles inside atom & also to explain the structure it is necessary to assume charged particles.As it has been assumed that there is positively charged particles -protons in center of atom it  is necessary to assume negetively charged particles which are called electrons.
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Spin related to the total angular momentum of a particle. It is found that the angular momentum of, say, an electron, is not simply that deriving from the orbital motion. There is an additional component with size 1/2*hbar where hbar is Planck's constant divided by 2pi.\n\nIn general, an angular momentum of size k*hbar allows several projections in value ranging from -k*hbar to +k*hbar with k increasing by integers. For the electron, that allows values of (+-)(1/2)hbar. This all follows from the general theory of angular momentum in quantum mechanics.\n\nNot every particle has spin 1/2. For example, a pion has spin 1 (more accurately 1*hbar) and can have projections -1,0, or 1.\n\nThose elementary particles with whole integer spin are called bosons and are usually involved in carrying force. Those with half-integer spins are called fermions and satisfy the Pauli exclusion principle.