Can anyone explaine how to do valeny numbers in chemistry?
954154
Valency number is the combining power of an atom or group of atoms and is used to work out the formulae of compounds. It used to be defined as how many hydrogen atoms am atom or group could combine with or displace. Nowadays it is the number of electrons the element or group can give, take or share. A sodium atom will give away one electron so it has a valency number of +1. Chlorine will take an electron so it has a valency of -1. When working out the formula of a compound the valency numbers must add up to zero. So in sodium chloride there is one of each atom as the +1 and -1 add up to 0. The formula is NaCl. The group sulphate SO4 has a valency number of -2 and so in sodium sulphate you would need two sodiums (each +1) for one sulphate and so the formula of sodium sulphate is Na2SO4.  Copper has a valency of +2 so copper sulphate would have one copper and one sulphate group (+2 and -2 = 0) so its formula is CuSO4. If you end up with a formula with more than one of a group - the group has to be enclosed in brackets as in Copper nitrate where the nitrate, NO3  is -1 and the copper is +2 you need 2 nitrates. The formula is Cu(NO3)2\nCarbon can share 4 electrons and hydrogen can share 1 electron. So carbon is considered as -4 and hydrogen +1. The formula for the simplest compound of carbon and hydrogen is therefore CH4 (methane).
799202
for those questions, all you have to do is translate them into the equation\ncheck chemtutor.com for hellp, it explains it much clearer than i can
185839
an easy way to know how many valence electrons are in an atom is by looking at the group number.. boron is in group 3 so it has 3 valence electrons... so you put 3 dots around Br
861190
There is a secret to it.  It is called DEMINTIONAL ANALYSIS.\n\nYou sound as though you are starting your first chem class, and probably in high school, so learn dementional analysis also know as the factor lable method and everything else will flow.\n\nThe chemical formulas actually tell you what you are working with, and yes it may seem silly that one little number misplaced or not placed at all, or even the wrong number could make a difference but they do.  That one little number in a formula means it is an entirely different compound with entirely different properites (some of the time).\n\nYou need it because this day in age any jobs in the med field or high paying jobs want people who have proven themselves to be intelligent and taking chem will certainly do that.\n\nIf you put some good hard studying into it you will get it.  Go to tutorial or get a home tutor what ever you need to get it do so.\n\nDon't give up the fight, stay strong!  Chem is really fun you just have to give it some time.\n\nThink of it like this, anything that you can buy had a chemist involved with it at some point before you bought it.  That is power!
922214
If you write the formula wrong, then you will calculate the formula weight wrong (too many or too few of one atom in a formula will translate to an incorrect formula weight). Then, when you try to figure out how many moles of the compound you have, your moles will be wrong too. And THEN, if you try to work out the stoichometry of a reaction using the incorrect formula, your mole RATIOS will be wrong, and thus you will get a wrong number when you try to determine the expected yield of a product in a reaction. (Not to mention it probably won't balance with an incorrect formula). If you're making up a solution using a wrong number of moles (see above), your molarity (moles per liter solution) will be wrong too. Everything will be wrong if you don't get your chemical formula right!
342540
Take the mass of the substance of interest, divide it by the total mass, mulitply by 100.\n\nIf you need to find the percent of an element within a compound, you convert mass of the compound to moles, and then determine the number of moles. \n\nThe number of moles of the compound will be equal to the number of moles of the element multiplied by however many atoms of that element are in the compound.\n\nFor example, if you have 3 moles of NH4OH, then you have 3 moles of N in that compound, and 15 moles of H in the same compound.\n\nOnce you have the number of moles of your element of interest, you convert it back to grams. Then divide that by the total weight of the compound and multiply by 100.\n\nHope I haven't been too confusing.
533429
well..write them down ...try to derive them (if their derivation is simple enough or else skip it )......\n\ntry to connect each formula with other one with a hint ....a small hint will help u to recollect other one ....\n\ntry to do at least one problem based on each formula
938474
The reason why you sometimes multiply by 1/2 or -1/2 is because you don't need the whole number they gave you because the reaction might only require (for instance) half of the products and reactants shown in equation (1). In this question you would have had to multiply by -1/2 if the final reaction had said 1/2C2H4(g) + 1/2H2O(l) ----> 1/2CH3CH2OH.  Another example would be if the final equation required 2 moles of something but the other equations you were working with had 4 moles in its equation. But in this case, you must multiply the first equation (1) by -1 because you need to flip the equation around in order to get the ethanol (CH3CH2OH) on the products side of the final equation. Sometimes you need more moles than what is given so you can also multiply by 2 or -2 or whatever you need.\n\nSo in short your math should look a little something like this:\n[(-1) x (-1367) ] + (-1411)=\n1367-1411=\n-44kJ
740045
http://www.wellesley.edu/Chemistry/chem120/titrate1a.xls\n\n\nstep by step
847953
If you know the mass ratio of the components of a compound you can determine the empirical formula.  What you have to do is convert the mass ratio into a percentage of the compound.  Then assuming you have a 100 gram sample the percentages would be the grams of each element.\n\nThen divide the grams of each element by each element's atomic mass.  This gives you the moles.\n\nThen divide the moles of each element by the smallest value to get an integer value.  If one or more of the values is not an integer, multiply by the smallest number you can to get whole numbers.  Then the numbers will be the number of atoms of each element in the compound.\n\nYou determine the mass ratio by quantative analysis.
852560
Sn has a valence (charge) of +3, that is also its' oxidation number.\nSn had 3 valence electrons it lost so the next lowest level would have eight. Having lost the three electrons gave it a +3 charge.  \nNormally Sn has +4 or +2 as a oxidation number. It's charge in this molecule is +3 (an odd occurrence), I think it is written incorrectly, having never seen Sn as +3.\n\nCl has a charge of -1, it gained one electrons because it had 7 valence electrons, gaining the one gave it eight. \n\nA compound must be neutral, so three Cl are needed to counter the one Sn.
236619
There are several steps used to do Lewis Dot Structures.\n1) Determine the number of electrons required ( in this example there are 40 electrons required)\n2) Determine the number of valence elestrons ( there are 6 +6+6+6+6 = 30 ), however since you have a -2 formal charge there are 2 extra electrons, which means you have 32\n3) Determine the number of bonds (subract the number of valence electrons from the total required and then divide by 2) ie: 40 - 32 = 8/2 = 4 bonds\n4) write the atom symbols on this page ( in this example you're going to write Se in the center with one Oxygen on every side)\n5) connect with the number of bonds that were calculated\n6) fill in electrons until all the atoms have conformed to the octet rule except for hydrogen\n7) then count the number of electrons shown to check your work\nAnswer: 1 bond connects each Oxygen to the one Selenium and each Oxygen is going to have six dots on the outside and Selenium is going to have four dots.
777428
well actually me and you are in the same situation. im trying to find out how to write wrod equations into a reaction. lol but neway i just learned how to balance equations its very simple.\nFe2O3+CO--Fe+CO2\n:draw a box around each set of elements:Fe2O3 would b in a box CO would be in a box and so forth.\n:then write out a diagram of how many atoms each element has:\nEx: Element/ Before/After\n      Fe          2         1\n      O            4         1\n      C            1          1\n:Then Write numbers in front of each of the boxes until the inventory for each element is the same both before and after the reaction. Now, what happens when we put a number in front of a formula? Basically, anything in that box is multiplied by that number, because we're saying that we have that many of that kind of molecule. \n:Now do this until the diagram is equal on both sides\nAND YOU HAVE YOUR BALANCED EQUATION
119628
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?
84780
!!!!!!!!!!!!!!!! \nI think rather u wanted to ask how can u predict the formula of a chemical reaction!!\nFirstly, we have to determine the moles of reactant taking part.(It can be done easily, think A reacts with B, just mix 1 mole of A with the same amount of B.)\nThen determine what are the different products and their amounts.\nAll u have to do is some calculations..................\nRemember its not as easy as it sounds.
241974
Just type the numbers in a search engine.  You probably will need to put them in quotes.\n\nAlso, http://chemfinder.cambridgesoft.com/
740485
Look up in Hand book of chemistry and mathematics, you school library will have it. Your professor should also have it.