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    • #7 - Ionic Bonding

    Remember the octet rule that atoms strive to be in low energy? and that the best way is by bonding with another element? Well keep that in mind as you try to form your very first chemical bonds.

    The first thing to do is to remember how many electrons each atom has in it�s outer shell. This can be easily figured out by just looking at the periodic table

    Notice each group. The vertically arranged elements have the same amount of electrons in their outer shell. Here�s a table to help you:

    Atoms in columns Numbers of electrons in outer shell
    H, Li, K, Rb, Cs, Fr
    1
    He, Be, Mg, Ca, Sr, Ba, Ra
    2
    B, Al, Ga, In, Ti
    3
    C, Si, Ge, Sn, Pb
    4
    N, P, As, Sb, Bi,
    5
    O, S, Se, Te, Po
    6
    F, Cl, Br, I, At
    7
    Ne, Ar, Kr, Xe, Rn
    8

    In ionic bonding, with the variations in number of electrons, only certain numbers of a certain 2 elements can combine where every atom is following the octet rule. It�s your job to determine how many.

    For example, find the chemical formula when sodium(Na) and chlorine(Cl) are mixed.

    Well...

    Sodium has one outer electron

    Chlorine has seven outer electrons

    All chlorine needs to achieve 8(which is good) is to get one extra electron from Na.
    Ironically, Na only has one electron to give away to have 0(also good) in it�s outer shell.

    They then suddenly bond
    and after cleaning up become this:

    NaCl

    This is a chemical formula.

    Here�s another, harder example: bond aluminum(Al) and oxygen(O).

    Hmmm...

    Aluminum has 3 outer electrons

    oxygen has 6 outer electrons

    Oxygen needs 2 electrons to get to 8,
    of course it can take the two from aluminum,
    but it will have one left (which is not good for the aluminum)

    But, what if we use a second oxygen that also needs two electrons to get to 8?

    This also causes a problem because there�s only one electron going around,
    so lets add another aluminum with 3 more electrons.

    Oh wait, there�s 2 more unused electrons left, why don�t we add another oxygen who needs exactly 2 to take!

    Now lets add up the number of atoms used:

    2 aluminum(Al) and 3 oxygen(O) atoms used

    The number of times used is put in subscript right after the symbol

    Al2O3

    This is a chemical equation!
    (remember, they always form a bond)

    - Here�s something about this you should think of:

    • each oxygen needed 2 electrons to get to eight
    • since there were 3 oxygen atoms used, they needed 6 electrons total (2 x 3=6)
    • aluminum had 3 electrons to give away so it can have zero in it�s outer shell
    • and there were 2 total aluminum atoms used, hence 6 electrons were given away
      (3 x 2=6)
    • so... (# electrons Oxygen took) = (# electrons Aluminum gave)
    • I know, very obvious.

    - Here�s another cool thing to think about, and to make your ionic forming easier:

    • since aluminum is bonding with oxygen, which needs 2 electrons, there will be 2 aluminums used
    • also, since oxygen is bonding with oxygen, which can give 3 electrons, there will be 3 oxygen�s used
    FREAKISH HUH?

    this can work with other compounds too:

    Calcium and Chlorine
    Calcium can give 2 electrons
    Chlorine needs 1 electron

    CaCl2

    it makes sense because with calcium having 2 electrons, you can share those two electrons with two chlorines (each only needing one)!

    Hang In There!

    I know bonding may seem difficult at first, but the only way to make it easier is to practice, practice, practice! Ask your teacher for extra problems. In fact, here are some now:

    1. Combine Calcium(Ca) and Oxygen(O)
    2. Combine Lithium(Li) and Phosphorus(P)
    3. Combine Sodium(Na) and Sulfur(S)
    4. Combine Aluminum(Al) and Fluorine(F)
    5. Combine Potassium(K) and Oxygen(O)

    Making ionic bonds will get easier with the next lesson.

    Answers:

    1. CaO
    2. Li3P
    3. Na2S
    4. AlF3
    5. K2O
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