can anyone help me understand the chemistry term Zeff?
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Zeff, Z (subscript "eff") stands for Effective Nuclear Charge.\nZeff represents the effective pull on electrons of interest (usually the outermost electron).\nIncreased number of protons increases Zeff.   First ionization energy is a reflection of Zeff.  Zeff decreases as the number of orbital layers increase primarily due to shielding of underlying electrons.\nGeneral periodic trend:  Highest at Helium, draw diagonal arrow down towards Cesium (lowest).
574078
This might help :)\nhttp://www.chemicalforums.com/index.php?board=8;action=display;threadid=3263
292071
What class was this in? What grade level? What text were you using?  I may be able to help you if I know the context in which the question was raised. I have a feeling that I am not getting all the information you had. Please tell me and maybe I can help. I am an old chemist and microbiologist.
425620
its a method of seperating individual molecules from a compound by placing samples on a special sheet coated with a material that will allow the molecules to seperate easily.  Then you put the place with samples in a developing chamber that will pull the molecules apart based on polarity.  That's not the best description in scientific terms, but that's pretty much how it works.  You just compare the distance each molecule traveled with the distance known molecules would travel in the same situation and it gives you a pretty good indicator as to what the unknown compound is composed of.
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Keywords:\n              Help\n\nCarbon has a unique place in our lives. Each living cell, food, wood, paper, petro-chemicals, cooking gas, perfumes, etc are all made up of carbon. Chemistry of carbon compounds is known as organic chemistry. Organic chemistry encompasses study of all carbon-hydrogen compounds. These are also called hydrocarbons. Inorganic carbon chemistry is the study of oxides, nitrides and allotropes of carbon.\n\nThere are many differences between organic and inorganic compounds. Organic compounds are mostly insoluble in water. They have low melting points and exist by forming covalent bonds. Inorganic compounds on the other hand usually dissolve in water and have high melting points. Inorganic compounds can be formed due to either ionic or covalent bonds. Another characteristic of organic compounds is that they are inflammable.\n\nCarbon has 6 protons, 6 neutrons and 6 electrons. Its chemical symbol is 12C 6. Its electronic configuration is 2 electrons in the K-shell, and 4 electrons in the L-shell. In principle it should either give up or borrow 4 electrons while forming compounds. But it doesn’t form ionic bonds at all. It likes to share its four electrons with other atoms and form covalent bonds instead. Carbon covalent bonds are the strongest in nature.\nWe might expect that a carbon atom to form three bonds of one kind using the p orbital electrons and one bond of another kind using the s orbital electron. But this does not happen!! The one 2s and three 2p orbitals mix together and give rise to four new altogether different types of orbitals. This is called  hybridization and is seen only in carbon atom. The four orbitals are at an angle of 109028’. This is called tetrahedral or sp3 (pronounced as sp three) type of hybridization. There are sp2 and sp types of hybridization also.
1086041
all the information you need is in the handy periodic table.   First, think about the charges of the molecules....\n\n In the molecule CuSO4, copper has two electrons to give.  The SO4 molecule wants TWO more electrons to acheive noble gas configuration (a stable electron state).   This appears to be a match in heaven.  \n\nWell all is fine until Zinc comes along.  If you look at the periodic table, Zinc is just to the right of copper.  It too has 2 electrons to donate......but, it is more electronegative than copper. (remember, electronegativity  is the lowest in the bottom left corner of the table(Fr) and increases on  a diagonal path  with F being the most electronegarive.)  \n\nSince Zinc is more reactive than Copper,  a replacement reaction occurs.  Zinc bumps Copper off of the SO4 molucule.  Zinc can be whitiish to yellowish in solution.  As all the Zinc is coming off the rod, it bumps the copper off the SO4 and also disperses the colour of the copper.  If you had one drop of blue dye (the copper), but added a cup of milk. ( the Zinc)...... you would barely see the blue color.
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http://hyperphysics.phy-astr.gsu.edu/hbase/chemical/water.html\n\nsee the picture here!
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1) O(2) = dioxide\n\n2) SeF(6) = selenium hexafluoride\n\n3) Si(2)Br(6) = disilicon hexabromide\n\n4) SCl(4) = ? sulfur tetrachloride\n\n5) CH(4) = carbon tetrahydrogenide\n\n6) B(2)Si = diboron silicide\n\n7) NF(3) =nitrogen trifluoride\n\ni just learned that today they might not all be right
436191
Uh, the rest of the question isn't appearing. But it's an equilibrium solubility problem. Write a reaction:\n\nMgF2 --> Mg+2 + 2F-\n\nKsp = 5.52e-9\n\nFill in the values on the ICE table (I don't know them, the numbers are missing), and set an equation up.\n\nKsp = [F-]^2 * [Mg+2]\n\nSolve with the numbers from the ICE table. Remember that those concentrations in the above equation are the equilibrated concentrations, not the initial.\n\n\nHope this helped.
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There is a very large book called "The Handbook of Chemestry and Physics"  This is a very good reference.\n\nAlso, at Barns & Noble there is a forumla sheet called Physics (SparkCharts).  Very helpful.\n\nFinally, look for the Physics for Dummies.  I have found that when tutoring and teaching, the explainations help me to better understand what is happening in terms that I can communicate.\n\nGood luck in your studies.
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Of what?\n\nπ= i*C*R*T\n\nT= absolute temperature (in Kelvin)\nR= the gas constant in whatever units you need to express osmotic pressure (e.g. if you want π in atm then R=0.082 L*atm/(mole*K))\nC= the concentration of your solute in mole/L\n\nand...\n\ni is the van't Hoff coefficient.\nFor non-electrolytes i=1\nFor strong electrolytes i= the number of ions that are produced by the dissociation according to the molecular formula e.g for NaCl you have 2 ions (1 Na+ and 1 Cl-) so i=2, for CaCl2 3 ions (1 Ca+2 and 2 Cl-) so i=3.\nFor weak electrolytes, if n is the number of ions coming from the 100% dissociation according to the molecular formula and a the degree of dissociation then i=(1-a)+na. E.g. if we assume for CH3COOH a=80% i=(1-0.8)+2*0.8= 0.2+1.6=1.8
1040448
ask your chem prof or tutor ..it's hard to explain over the internet!
352077
Thanks NeuroProf.\n\nThe molecule AsF5 is trigonal bipyramidal in shape. First lay out all the bond pairs in that shape and then see if the 'pulling effect' of all the bonds cancel each other. Here, there are 3 bond pairs (of Cl) at the corners of the triangle, 1 bond pair at the bottom and 1 at the top. The Cl at the top pulls electrons and the pulling effect is cancelled by the one at the bottom. Considering the 3 bond pairs left in the middle, 2 are angled at 120 degress and one is at 90 degrees to the top and bottom bond pair. So the pulling effect of the 2 pairs is cancelled by the one at 90 degrees. Overall dipole cancels out and there is no charge distribution, so the molecule is non-polar.\n\nIn BrF4- (with square planar shape), the pulling effect of the lone pair at the top is cancelled by that of the lone pair at the bottom. This leaves 4 F atoms arranged at the corners of the square in the middle. The pulling effect(dipole) of 2 diagonal F atoms will cancel because they are in the same plane and are the same atoms. Hence all the 4 dipoles cancel out and that of the lone pairs too, so the molecule is non-polar.\n\nIn GaI3, the 3 I atoms are arranged in a trigonal planar manner. The dipole of the 2 I atoms at the sides will cancel, but the I atom at the top is not paired with any other atom at the bottom, so the dipole cannot cancel out. Since overall dipole moment is not equal to zero, the molecule is polar.\n\nAre you sure the molecule is SbF6- and not SeF6? If it's SbF6 then the shape will be square bipyramidal or octahedral (similar to BrF4-). The dipole of the 2 F atoms at the top and bottom will cancel and that of 2 diagonal F atoms will cancel and overall dipole will be zero, so the molecule will be non-polar.
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Hmm, kinda hard to help you here, since we can't see all your options for the first two.  The ellipses (. . .) indicate that you have more in your message than is being displayed.  Perhaps if you retyped them, it would be easier for us to help.\n\nHere's what I *can* help with:\n\nHalogens:Reactive as Noble Gas:STABLE\n(the halogens are very reactive gases, while the noble gases are extremely stable, almost to the point of being inert)\n\nOxygen:molecule as chloride:ION\nOxygen gas is a molecule, while chloride is the ionic form of chlorine\n\nRatio:subscript as oxidation number:CHARGE\nthe ratio of components in a mixture is denoted by the subscripts, as the oxidation number of an atom is denoted by its ionic charge
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Ionic compounds are basically defined as compounds where two or more ions are held next to each other by electrical attraction. One of the ions has a positive charge (called a "cation") and the other has a negative charge ("anion"). Cations are usually metal atoms, and anions are either nonmetals or polyatomic ions (ions with more than one atom).\n\nA molecular compound is made up of all non-metals. The bond that forms between the atoms is by the sharing of electrons, unlike ionic compounds, which are made by the transfer of electrons.\n\nIn the case of NaH, this is a ionic compount and this is a strong base. \n\nAcid is defined as a compound which donates a hydrogen ion (H+) to another compound (called a base). You can also see it this way: An acid is a proton donor and a base is a proton acceptor. The acid is said to be dissociated after the proton is donated.\n\nAbout naming of compounds, read the book. It's a long discussion.
943195
It has been many years since I even cracked the book on crystal field theory, but I refreshed myself a bit here:\n\nhttp://www.unine.ch/chim/chw/Chapter%204.html\n\nBasically, the difference in splitting (delta value) decreases as you go down a group and increases by about 50% as you add positive charge on a metal cation. Other factors are covered on that page as well. Thanks for the reminder that I took a graduate inorganic chemistry class once back in the early 90's! I assure you that, at one time, I actually understood it, but I haven't used it in so long...well, you get the picture!\n\nP.S. (I had forgotten that it replaced VB theory, which I was supposed to teach my students but ran out of time!)
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So, usually the best way to do these is to just fiddle with them until you get them right, but for the sake of it, let's go with a systematic approach using algebra.  First we assign a variable in front of each of the terms on the left and right like:\n\nx Pb  +  y H2O  +  z O2  -->  a Pb(OH)2\n\nSo now we'll write down equations to make sure that we have the same numbers of both sides of each *element*.  I'll do this by writing down the variable in front of each compound in your equation (so x, y z and a) and then multiplying those by the number of times an element exists in that compound.  (So when I'm writing the equation for hydrogen, the H20 term will be 2*y, because y is the coefficient in front of H20 and H occurs twice in that compound).\n\nRemember, the number of any element on the reactants (left) side equals the number of that element on the products (right) side.\n\nFor Pb: x = a, because Pb shows up only once on each side with a subscript of 1, those two compounds will have to be present in the same molar amounts.\n\nFor Hydrogen: 2y = 2a\n\nFor Oxygen: y + 2*z = 2 * a\n\nSo now we have three equations:\n\nx = y\ny = a\ny + 2z = 2a\n\nBut four unknowns, which is fine because we'll just solve for them in terms of one of the variables and then simply choose the last variable to make all the numbers nice.  So solving the equations in terms of a:\n\nx = a\ny = a\nz = (2a - y)/2 = (2a - a)/2 = a/2\n\nSo now we have x, y and z in terms of a free parameter, a.  We'll just choose a = 2, for example, to make x, y and z all turn out as integers.  So now we've chosen:\n\nx = 2\ny = 2\nz = 1\na = 2\n\nSo the balanced equation is:\n\n2 Pb + 2 H2O + O2 --> 2 Pb(OH)2\n\nMake sense?