why is the weight of electrons not included in the atomic mass. what id atomic mass weight.?
358467
because electrons mass is insignificant to the mass of the nucleus of the atom. omitting the electron mass is prctical because there is soo much space between electrons and other atoms in a molecule at any given time that 99.9% of the density that effects the behavior of a moving molecule come from the nucleus itself.
948808
Electron is simply the smallest and ligthest subatomic particle inside every atoms. as you know, atom consists of protons (positively charged), neutrons (no charge) and electrons (negatively charged). you can imagine atoms to be like a planet which has meteors orbiting around it. the planet represent the nucleus which consists of the protons and the neutrons. and the meteors around are representing the electrons. due to its light weight, electrons move around in an incredible speed around the nucleus. however, electrons do not escaped from the nucleus because they are bounded by forces which keep them in tracks. you can check it out in www.wikipedia.com if you need more info on electrons :D . GL for ur science fair anw.
184661
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.
365764
Your second statement is correct, i.e proton mass+electron mass = constant mass and energy.\nok, This is with reference with another question you asked about mass defect(and chose my answer as the best, thanks). The sum of individual masses is greater than the actual mass of the atom. I am sure of this because this is what explains the stability of an atom(less energy, more stable).\nI'll give you an example which I took from my chem book\n\nMe = 0.0005486 amu(atomic mass unit)\nMp = 1.007277 amu\nMn = 1.008665 amu\nMe,Mp,Mn are masses of electron, proton and neutron respectively and 1 amu = 1.6605 x 10^-27 Kg\n\nOne He atom contains two electrons, two protons and two neutrons.\nSumming up the values of the constituents you get 4.032981amu as the expected mass of the atom.\nHowever the actual mass of the atom is 4.002603amu\nDifference = 0.030378 amu\n\nThe formula to find the binding evergy(energy required to bring the constituents together) is: mass defect x 931.48MeV\n\nHere that would be 0.030378 x 931.48 = 28.296 MeV\ni.e that is the equivalent of the mass defect in energy.\nThe '931.48' part is calculated using Einstein's formula E=mc^2.
78209
Nope, the magnetic information (not electronic!) doesn't weigh anything, it's all related to the orientation of the "magnetic moment" (up or down) of the atoms i.e. the way atoms are turning (to make it simple). they're not heavier if they turn in one sense than if they does in the other
199003
a proton has a weight of approximately 1836.15 electrons
12366
Hi again,\n\n    Well you see, as you know electrons are added up in the 3d orbital in galium, right? So with the increase in number of electrons, the no of protons i.e atomic number also increases. So now the outermost p electron in Al is attracted by 13 protons. But that in galuim is attracted by 31 electrons. So the force of attraction is much more. Now in other atoms, these outer electron attraction is balanced by counter electron electron repulsion. But the added d electrons  cannot shield the outer p electrons much from the force of attraction of the highly charged nucleus. This is similar to the reason why the transition elements contract on increase in at no. Other examples are lanthanide and actinide contractions. If you still dont get it,\nmeet me on Yahoo Messenger. My id is jchemisch. I will talk to you about it. All the best. Hope i can help you if you need!!
854263
The mass of the electron has been measured to an accuracy of 0.17 parts per million.  That's consistent with all electrons having the same mass, but not enough to rule out the possibility of more than one mass value where all are within the accuracy limits of our measurements.  The proton mass is known to the same accuracy.\n\nThe charge of the electron has been measured to 85 parts per billion.  No measurement has found a difference in magnitude between the electron and proton charge.\n\nTo answer the question, I would try to think of experiments whose outcome would be different if the mass or charge differed.  I would also run lots of simulations with varying assumptions for those values.  Quantum effects make it extremely difficult to measure the results of such experiments.
331142
If you sum up the masses of individual neutrons, protons and electrons in an atom and compare it to the mass of the atom itself you will find it to be slightly higher. This difference in mass is called mass defect. The 'missing' mass is actually the energy required to bring together the individual protons, neutrons, electrons to form the atom. Energy can be calculated using Einstein's formula E= mc^2, where E- energy, m-mass defect, c-speed of light
797180
Atomic mass depends on the element. It accounts for all isotopes and does a sort of weighted average, depending on how often the isotope occurs in nature.\nMass number depends on the isotope.\n\nFor example, atomic mass of hydrogen is 1.0079. The mass number of most hydrogen atoms is 1. Deuterium is an isotope with a neutron in its nucleus, so its mass number is 2. Tritium is an isotope with two neutrons, so its mass number is 3.
838528
No elements are there.\n(If it would have been there, one would have to discover another quantum number in order to distinguish between them).\n& like the previous answerer said it would have been violated the Pauli's exclusion principle.\nThe quantum numbers are there to distinguish between different electrons.
29223
electrical weight? um i dont think thats a real term, if you mean an electron has no mass then in fact ot does, its just very small. And to answer your question:\n\nmoving photons have momentum and momentum must be conserved in a collision so the electron would move.\n\nI assume you are talking about the photoelectric effect, which is slightly more complicated as what happens there is that the photons give the electron kinetic energy so they jump out of thier energy level and move freely thus creating a current.
360137
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.
1138448
Look on a periodic table.\n\nIt should be listed below the atomic number as a decimal value.  The mass number is an average mass (in atomic mass units) of an element, based on different isotopes.  It equals the number of protons + the number of neutrons in the nucleus.
450990
The mass of a nucleus indicates the number of protons and neutrons present in the nucleus. An element can have more than one isotope eg Carbon 12 and Carbon 14. The former has 6 protons and 6 neutrons, The latter 6 protons and 8 neutrons. \n\nThe atomic weight of an isotope refers to the numbers of protons AND neutrons present. The atomic number of an element refers to the number of protons in all its isotopes.\n\nHydrogen, though normally just a solo proton in its nucleus, does have two isotopes, deuterium, with 1 neutron, and tritium with two neutrons.\n\nA recent question asked about silver, how many of each in its nucleus. Its atomic number is 47, so clearly 47 protons. Naturally-occurring silver is given as having  an atomic weight of 108, so answerers answered 61 neutrons.\n\nHowever there is a subtlety they missed..\n\nNaturally-occurring silver is a mixture of Ag 107 (60 neutrons) and Ag 109 (62 neutrons). (Slightly more than 50% of the former.).\n\nSo the average atomic weight of the two isotopes is 108. But there is no Ag 108 isotope present. The wrong inference was drawn.\n\nSeveral people above are confusing atomic weight and atomic number, and what they each mean. So if you don't understand several of the answers it is because they are jumbled versions of the true picture.
263751
The mass of protons and neutrons are nearly identical, the mass of an electron is about 1/1840th the mass of a proton, thus it is negligible, so you can't really tell its there.
95148
Actually, the mass of a proton is 1.00727664669 atomic mass units.\n\nAn atomic mass unit is defined such that Carbon 12 is exactly 12.  The carbon atom weighs less than 12 times the proton (because of nuclear binding energy).