Dr. Walt Volland, revised July 8, 2010


What is the easiest way to determine the charge on the cation formed by a metal? Why do calcium and magnesium form a +2 cation instead of +3 ion? Why does chlorine, Cl, form a -1 anion and not a -2 anion?


The group number for a metal generally equals the positive charge on the cation.  Metals like Li, Na and K in group 1A typically form ions with a +1 charge.

Calcium and magnesiun have two valence or outer electrons. The energy needed to remove these electrons is usually available in chemical reactions with nonmetals. The removal of a third electron requires more energy than is available in chemical reactions. This means we never see +3 ions for these meatals.

Chlorine is in group 7A. Chlorine has seven valence or outer electrons with a subshell population of 3s23p5 . There is space for one more electron in the 3p subshell. The placement of this electron completes the "s" and "p" set of subshells for chlorine. there is a release of energy when this additional electron enters the subshell. There is no -2 ion because this requires adding an electron to the 4s subshell on a negative ion, Cl1-. There is a repulsion between the Cl1- and another electron. This means energy would be needed to force the electron and the Cl1- ion together.


Predict, write and name the formula units for the compounds formed by the ion pairs listed below?

Answer: -----------------------------



Fe3+ with Cl1----------------------------------

Ca2+ with PO43-------------------------------

NH4+ with SO42------------------------------

FeCl3 iron (III) chloride--------------------

Ca3(PO4)2 calcium phosphate----------

(NH4 )2SO4 ammonium sulfate

Fe2+ with Cl1----------------------------------

Ca2+ with HCO31-----------------------------

NH4+ with CO32-----------------------------

FeCl2 iron (II) chloride--------------------

Ca(HCO3)2 calcium hydrogen carbonate

(NH4 )2CO3 ammonium carbonate

Zn2+ with Cl1---------------------------------

Ca2+ with NO31------------------------------

Al3+ with SO42-------------------------------

ZnCl2 zinc chloride--------------------

Ca(NO3)2 calcium nitrate---------------

Al 2(SO4 )3 aluminum sulfate

Cu2+ with F1----------------------------------

Ca2+ with OH1--------------------------------

K+ with SO42----------------------------------

CuCl2 copper (II) fluoride-----------------

Ca(OH)2 calcium hydroxide------------

K2SO4 potassium sulfate----------------



Draw the electron dot structures for the following atoms and ions. How do you know the number of additional electron dots needed to convert an atom like sulfur (S) to an anion like sulfide, S2-? The charge on the ion tells the number of "extra" electrons that must be added to the neutral atom. The charge on sulfide is -2. This means the sulfur atom needs two more dots to complete the octet. The formation of cations requires the removal of electrons from the neutral atom to form the positive ion.


fluoride ion F1-----------------------------------------30%-------

hydroxide ion, OH1---------------------

potassium ion, K+-------------------------------------

bromide ion, Br1-------------- barium atom, Ba oxygen atom, O
nitrate ion, NO31- ------Ne-neon atom    H1-, hydride ion



Explain why all hydrogen containing compounds are not acids like HCl(aq).

What happens in a solution of a strong acid like HCl(aq) that makes the mixture acidic?

What happens when water and ethanol, CH3CH2OH, are mixed?

Answer: When water and HCl are mixed the HCl molecule breaks up or dissociates to release H+ and Cl1- ions. The bond between the hydrogen and chloride is weaker than the attraction between water and the H+ and Cl1- ions. The release of the H+ ions is what makes the mixture acidic.

When water H2O and alcohol mix the molecules of alcohol remain intact. Most the most part the molecules do not break apart to form ions. The mixture is a uniform distribution of H2O molecules and CH3CH2OH molecules. There are no H+ ions released. The solution is not acidic.



What happens when NaOH(s) is dissolved in water? What ions are formed in the solution? Tell whether the solution is acidic or basic.

Answer:: The solid sodium hydroxide dissolves in water. The water molecules are "polar". They have a positive pole or end associated with the hydrogens and a negative end or pole associated with the oxygen end


Many water molecules have their positive end attracted to an hydroxide ion. This attraction is so great that the water molcules are able to pull the hydroxide ion out of the solid. This kind of process is repeated bewteen diferent water molecules and the sodium ion. A different group of water molecules pull a sodium ion out of the crystal. The process is repeated billions and billions of times until either the solid has completely dissolved or there are no more unassociated water molecules. In general terms people say sodium hydroxide dissolves to release sodium ions and hydroxide ions. The solution is basic.



What is the octet rule? Tell how the octet rule relates to the subshells in an atom. Why do you suppose hydrogen does not follow the octet rule? Do the atoms in row three, Na through Cl, always follow the octet rule? Does sulfur follow the octet rule when it forms the sulfide anion, S2-?

Answer: Atoms gain and lose electrons to form a rare gas electron shell population. This means an atom gains or loses electrons to complete nsnp set of subshells. Hydrogen cannot follow the octet rule because it has valence electrons in the n = 1 level which has a capacity for only 2 electrons. Generally the elements in row two follow the octet rule. The elements in row three such as sulfur in SF6 can violate the octet rule because the d subshell can be used to accommodate more than an eight electrons. Yes, sulfur follows the octet rule when it forms the sulfide anion.



Why is the charge on a chloride ion a minus one when the chlorine atom gains an electron to form the ion?

Answer: Chlorine is in group 7A. The chlorine atom has 7 valence electrons and has room for one electron in the "valence shell". The negative charge is -1 because the neutral atom has gained one additional electron to form the anion.

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