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  1. #1 Complex ions 
    icu
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    why do you need to put a 2 in front and at the back of NH_3? without it isn't is already balanced like below?can anyone explain this to me?



    thanks in advance. :-D


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  3. #2  
    Universal Mind John Galt's Avatar
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    If your equation is correct then the 2 is necessary because the reaction product consists of two NH3 components bonded to each silver atom, not one. There is a nice illustration here.


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    icu
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    Quote Originally Posted by John Galt
    If your equation is correct then the 2 is necessary because the reaction product consists of two NH3 components bonded to each silver atom, not one. There is a nice illustration here.
    but how do you know is 2 and not 3 or 4 when you are writing the equation?
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    Hello,

    When you’re balancing an equation you must have both atom balance and charge balance. – That is you must adhere to the law of conservation of mass and the law of conservation of energy. Remember that neither can be created or destroyed…
    So in your example you displaced a Cl with ammonia (NH3) – which means that a negative charge has been formed on the right side of the arrow and must be balanced.

    Therefore you must make a positively charged species on the left side as well to balance the Cl… Looking at silver on the periodic table you will see that 2 NH3(s) on the silver atom will give it a charge of + 1.

    Now, that you have the charges balanced you must go back to the left side of the equation and balance the atoms by changing the coefficients in front of them.

    *This may also help you understand this… If you have 1 mol of silver chloride in your reactants and 1 mol of NH3 then you will get a 50% yield because the NH3 must add to the silver twice. This will leave you with 50% of unreacted silver chloride and 0% of the NH3 remaining in a perfect world.

    Understanding how to assign charges arbitrarily for the transition metals is complex and I do not believe you will have to go into that kind of depth – but I have provided a link if you want to research that more.

    Otherwise for these problems just do the following:
    1. Check for net charges on each side of the reaction equation
    2. Make sure that the net charge on the right side matches the net charge on the left side
    3. To determine what the charge should be on each atom you will have to look at the electronconfiguration assigned by using the periodic table and then decided if you are adding or removing an electron in the reaction. Adding an electron will make the atom more negative and removing an electron will make the atom more positive.
    4. Once you have determined the net charges on each side go back and balance the coefficients of the atoms accordingly - remember that these coefficients correspond to the number of bonds needed to make the atom either more positive or more negative.. so if you need two bonds to NH3 to get a positive charge on the silver then you will write 2NH3 on the side of the equation where the NH3 is stand alone and NH3 subscript 2 on the side of the equation where NH3 is bound to another atom twice... and so on...

    For more information on assigning the electronic configuration of transition metals see this: http://chemed.chem.purdue.edu/genche...s.php#electron
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    Universal Mind John Galt's Avatar
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    Quote Originally Posted by chemist
    Looking at silver on the periodic table you will see that 2 NH3(s) on the silver atom will give it a charge of + 1.

    Now, that you have the charges balanced
    Can you explain how a charge of +1 represents a balanced charge?
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    Quote Originally Posted by John Galt
    Quote Originally Posted by chemist
    Looking at silver on the periodic table you will see that 2 NH3(s) on the silver atom will give it a charge of + 1.

    Now, that you have the charges balanced
    Can you explain how a charge of +1 represents a balanced charge?
    Sure, overall you have a neutral net charge on each side of the arrow because silver must be +1 to balance the Cl- therefore now each side of the arrow
    is balanced.. with a net charge of zero for each side.
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    I can see I have been away from chemistry for too long. I understand a balanced charge to mean that the resulting atom or molecule carries no net charge, either positive, or negative. In this case the complex ion carries a plus one charge. How is that balanced? What am I not grasping?
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    Quote Originally Posted by John Galt
    I can see I have been away from chemistry for too long. I understand a balanced charge to mean that the resulting atom or molecule carries no net charge, either positive, or negative. In this case the complex ion carries a plus one charge. How is that balanced? What am I not grasping?
    Hello,

    I’m not exactly sure what you’re not grasping. In this sense the term “balanced charge” refers to the overall “net” charge of all reactants as compared to the overall “net” charge of all of the products.
    If you add up the net charge for the left side of the equation you will see that the charge is zero i.e. neutral.. the law of conservation of energy dictates that we must also have a overall net charge of zero i.e. neutral for the products..
    So because the halogen has a charge of -1 it is necessary to bring the silver up to a charge of +1 in order to provide the overall net charge of zero for the products.

    Once the book keeping of the charges of each atom and each molecule is complete you have a net charge of zero for the products because (-1) + (+1) = 0
    i.e. the charges have been balanced - meaning that the net charge on the right side of the reaction arrow now equal the net charge on the left.
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    Well I now see the origin of my confusion. Thank you for sticking with me.
    You seemed to be saying that the complex ion had a balanced, i.e. neutral charge, which was obviously wrong. Now that I see you were referring to the equation as whole the confusion disappears.
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  11. #10  
    icu
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    Quote Originally Posted by chemist
    Looking at silver on the periodic table you will see that 2 NH3(s) on the silver atom will give it a charge of + 1.
    intresting, one thing i am confused about is how does 2 NH3(s) on the sliver atom gives a charge of +1?
    because the charge on NH3 is zero no matter how many you have right?

    thanks in advance.
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    Universal Mind John Galt's Avatar
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    The Ag is an ion, not an atom. It gave up one of its electrons to the chlorine, which is why the chlorine has a net negative unitary charge. (-1)
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    his page explains the terms complex ion and ligand, and looks at the bonding between the ligands and the central metal ion. It discusses various sorts of ligand (including some quite complicated ones), and describes what is meant by co-ordination number.

    Complex metal ions containing simple ligands

    What is a complex metal ion?

    A complex ion has a metal ion at its centre with a number of other molecules or ions surrounding it. These can be considered to be attached to the central ion by co-ordinate (dative covalent) bonds. (In some cases, the bonding is actually more complicated than that.)
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    Quote Originally Posted by icu
    Quote Originally Posted by chemist
    Looking at silver on the periodic table you will see that 2 NH3(s) on the silver atom will give it a charge of + 1.
    intresting, one thing i am confused about is how does 2 NH3(s) on the sliver atom gives a charge of +1?
    because the charge on NH3 is zero no matter how many you have right?

    thanks in advance.
    Hello,
    The reason that the NH3 remains neutral is because it is not covalently bound to the silver. It is a ligand coordinated to the silver therefore you will see no change in the NH3 for these purposes but you will see the change in the charge of the silver because coordination of ligands to metals will affect the charge…
    So because you have 2 NH3s ligands on the silver you will see the silver having a charge of +1 in this case because the NH3s are neutral ligands and the oxidation state of the silver going in.. If you change the charge of the ligands or the oxidation state of the silver you will have a different outcome for the charge.

    I hope this helps. : )
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  15. #14  
    icu
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    Does the two ligands coordinate to the sliver valance shell?

    thanks in advance.
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    Hello,

    yes that is correct.

    See this link for more info: http://chemed.chem.purdue.edu/genche...12/complex.php

    hope this helps. : )
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  17. #16  
    icu
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    Quote Originally Posted by chemist
    Hello,

    yes that is correct.

    See this link for more info: http://chemed.chem.purdue.edu/genche...12/complex.php

    hope this helps. : )
    I tired reading that but is just beyond my understanding. :P
    but i think it gives a +1 charge because the 2 neutral ligands gives a neutral charge therefore remains the same, am i right? :-D

    thanks in advance.
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  18. #17  
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    Quote Originally Posted by icu
    Quote Originally Posted by chemist
    Hello,

    yes that is correct.

    See this link for more info: http://chemed.chem.purdue.edu/genche...12/complex.php

    hope this helps. : )
    I tired reading that but is just beyond my understanding. :P
    but i think it gives a +1 charge because the 2 neutral ligands gives a neutral charge therefore remains the same, am i right? :-D

    thanks in advance.
    I understand.. unfortunately it is a little more complex than that.. the charge on the metal center is derived from the following...

    1. The original oxidation state of the metal that you are using
    2. the charge of the ligands that will be coordinated to the metal (in this case neutral)
    3. The type of bonding/coordination that is taking place...

    so just remember that you must first determine the oxidation state of the metal center without the ligands that are being added and then determine the charge of the ligands.. and in this case they are neutral as you have said so you get the silver at a +1 charge.

    So the charge on the silver does not remain the same - it in fact changes as you add each ligand.. whereas the charge of each individual NH3 ligand remains the same (neutral) because they are NOT covalently bound to the silver...

    hope this helps.. : )
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