chemistry question about quantum mechanics?
445231
It describes electron location in terms of probabilities.  The energy levels around a nucleus are not well-defined orbitals.  Rather, they are regions of space where an electron may be found.  Withing the orbitals, the electron's precise location can not be known.  According to Heisenberg's Uncertainty Principle, the more accurately we measure an electron's location, the more imprecise the measurement of its velocity becomes, and vice-versa.\n\nSo, the best description of an electron's location is that of an "electron cloud", which represents the region in space where an electron has the highest probability of being.
541986
The basic idea is that in any chemical reaction, the HOMO of one molecule interacts with the LUMO of another, and the result is that a chemical bond is formed. \n\nThere are two criteria for this to happen. First, the energy difference between the HOMO and LUMO must be small. Second, there must be enough overlap between the HOMO and LUMO for the bond to form.\n\nIt also turns out that in order to get good overlap, you must have the same symmetry of the two orbitals. The amount of overlap is calculated as the integral of the product of the two wavefunctions. If the orbitals have opposite symmetry, this integral cancels out to zero and you have no overlap. However, if the orbitals have the same symmetry, it's possible they can form a bond.\n\nThe Woodward-Hoffman rules are just an easy way to predict which reactions will have favorable symmetry so that orbital overlap is possible and the reaction can potentially form a bond. \n\nThe issue of heat vs light is an issue of which orbital is the HOMO. If you excite a molecule with uv light, you can promote and electron to the next higher orbital. This means that the HOMO is now different from the ground state, and will have a different symmetry than the ground state. As a result, it is going to overlap well with different LUMOs and allow for different reactivity.\n\nNeedless to say, the Woodward Hoffman rules simplify a lot of quantum physics into some very short and sweet rules with amazing predictive ability. Roald Hoffman definitely deserved the Nobel Prize in 1981 for this work, and there is little doubt that R. B. Woodward would have received his second Nobel had he been alive in 1981.
1138290
Look up stuff like Arrhenius equations. I don't have my phys chem text book to hand.\n\nFor part two, I think it's D, as I'm fairly certain it's not any of the others.
518644
The main advantage of quantum mechanics is " you can deal with atoms and single molecules which you can not do it in reality. So, with out performing some experiments in lab you can able to calculate some ther,o dynamic quantities of atoms and molecules..\nFor example, H2 molecule  energy, orbitlas orientations, electron density around the molecule... like these aspects you can calculate and visualize by quantum mechanics.. these are basic applications of quantum mechanics..\n\nGot it?
570126
It all comes down to two forces: the attraction between electrons and the nucleaus and the repulsion between the individual electrons.  This leads to a complex set of equations that do not have a solution. \n\nIf we assume that molecules behave as a combination of atomic states of only one electron, then we can try to formulate solutions of the equations (because the electron-electron repulsion term is zero). \n\nUnfortunately, the equations do not have a single answer. They have multiple answers. These answers have been called electronic configurations and are your different shells, sub-shells, etc. The actual quantum numbers are seen in the equations as solutions to the Schroedinger equation(HY=EY): n, l, ml, and ms.\n\nThe prevailing intepretation are that these states are energy levels which can be occupied by electrons as the form molecular bonds. \n\nMy university professor would probably remove my liver for such a poor description of the phenomenon, but this was always my best understanding of it.
832322
H2O has 8 valence electrons resulting to a triatomic bent 109.5 degrees.\nit will look like this \n\n                   ..  ..\n                     O\n                   /     &#92;\n                 H       H   \n\nthe 2 dots are lone pairs..  the distance netween the angles should be 109.5 degrees
222974
Two hydrogen atoms, one oxygen atom.  H2O
791559
Let's see, this may be a bit difficult to explain, but since no one else has so far, I figured I'd give it a shot.\n\nI don't have a periodic table in front of me, so I'll do my best to explain.  There is a double bond between N and one of the O's because of something called "in-bonds."  You determine the number of "in-bonds," or bonds in between elements by subtracting the number of valence electrons that you have all together from the number that you need for everything to be stable.  In this case, forget about H for the time being, and you have N03.  Each element needs 8 electrons to fill its valence shell right?  Multiply 8 by 4, since there are 4 elements, and you get 32.  However, you only have 24 electrons to go 'round.  The difference is 8, there for you can have a total of 8 electrons, or 4 individual bonds in between the elements.  It doesn't matter which O gets to share the double bond with N, as they are all the same.\n\nThe double bond was used in HNO3 and not NF3 because I believe you had enough electrons to go around, therefore there were no "in-bonds."\n\nI hope this helps to clear up your questions.
373953
Quantum mechanics deals with anything that can come in fixed quanta, which is basically everything if you get small enough!\n\nMass comes in its fundamental particles, but you have other fixed packets of energy that can be treated with particle behaviour.\nA photon is a packet of light.\nA phonon is a packet of vibrational energy.\nEven magnetic flux in a superconductor has a magnetic flux quantum.
1067262
This is covered in most quantum mechanics textbooks. I'm looking at the appendix to Albert Messiah's Quantum Mechanics Vol I. The wavefunction for n=2,l=0 is:\n\n(1/(a^3/2)) * 1/sqrt(8pi) * (1-r/2a) * exp(-r/2a)\n\nwhere a is the Bohr radius. Let's use units in which a=1. The probability density is:\n\nP(x) = 1/(8pi) * (1-r/2)^2 * exp(-r)\n\nThe radial probability density is the above times the area of the sphere:\n\nR(r) = 4pi * r^2 * P(x) = 1/2 * r^2(1-r/2)^2 * exp(-r)\n\nIf you want the radius of the location in space at which P(x) is maximal solve:\n\ndP(r)/dr = 0 (a quadratic equation)\n\nIf you want the radius at which the radial probability density is maximal solve:\n\ndR(r)/dr = 0 (a cubic equation)\n\nR(r) has two relative maxima. I think the one farther out is bigger. The expectation value of the radius <r> is:\n\n<r> = &#92;int_0^oo R(r) r dr \n\nstraightforward using &#92;int_0^oo r^n e^(-r) dr = n! etc.. The answer <r> should be 6a.
200774
well i cant help you with the lewis structure cuz i dunno what that is. but the bohr diagram is   um hard to explain without drawing it out. ill try. \nfirst you draw a circle and the number of protons and neutrons in them (#protons is atomic number and #neutrons is mass=#protons). and then you draw an orbital around that circle and draw 2 dots on that orbital (corresponding to 2 electrons, there is a max of 2 electrons in the first orbital). then you draw another orbital around it and you can put up to 8 electrons (dots) on it. and then if you need another one, then you can put up to 8 on it and so on. the number of electrons you have to put is the same as the number of protons. and dont draw the empty orbitals.\n\nhope that helps. let me know if u need more help. later
379019
The quantum number description of an electron *is* the electron, in a sense, so two electrons with the same quantum numbers would be the same electron.
112894
Haven't had chem in a while but maybe it would help to write out all the individual symbols.  Your second example would look like\n\nHHHPOOOO + MgOOHH  = MgMgMgPPOOOOOOOO + HHO\n\nthen you can see that the left side needs three Mg so you'd need 3 of the Mg(OH)2 to balance.  The left side also needs two P so there needs to be two H3PO4 there.  This makes a total of 12 H on the left, so to balance that you need 6 H2O on the right.  This also gives 14 O on the right to balance the 14 O you'd now have on the left.  So\n2 H3PO4 + 3 Mg(OH)2 = Mg3(PO4)2 + 6 H2O
791178
I HAVE A CHEMISTRY EXAM tomorrow. Actually a small test.lol\nwant answers go to the site below!
1036198
Orbitals are solutions to the schrodinger wave equation, quantum mechanics, taking into account translation, number, and rotation, letter.  The rotational levels, s p d f, are from the symmetry of the solutions.  With lower levels of translational energy the higher symmetries do not exist.\n\nsee the source from "Solution of Schrödinger equation: Overview of results" and down for a true mathematical explaination.
956604
Try it out in the lewis-dot diagram\n      ..        ..\nH-O-Ca-O-H\n      ..        ..
14608
Quantum mechanics is a fundamental physical theory that replaces Newtonian mechanics and classical electromagnetism at the atomic and subatomic levels and is the underlying framework of many fields of physics and chemistry, including condensed matter physics, quantum chemistry, and particle physics. Often, it is the answer to questions when general relativity fails.