Two atoms are walking down the street. Says one atom to the other, "Hey! I think I lost an electron!" The other says, "Are you sure??" "Yes, I'm positive!"

 Ions are charged particles.  These result when an atom gains or loses electrons.  REMEMBER: If the number of e - is not equal to the number of p +, then the particle will have a charge …  AND DOUBLE REMEMBER: Atoms “LOSE” electrons, they do not “LOOSE” them.

Cation is pronounced “cat – ion”, not “cay-shun.” Anion is pronounced “an-ion,” not “annie-on.” When writing ions, use the symbol for the element, and indicate the charge as a superscript to the right. Example: Potassium forms a +1 ion. K +1

 Cations have a positive charge.  These have lost electrons.  This is what metals do.  They generally have a +1, +2, +3 charge, but there are also higher charges among the transition metals.

Cations These have more protons than electrons since they have lost electrons. K +1 Has lost one electron – potassium ion. Ca +2 Has lost two electrons – calcium ion

 Anions have a negative charge.  These have gained electrons.  This is what non-metals do.  They can have a -1, -2, or -3 charge

 These have more electrons than protons since they have gained electrons. F -1 Has gained one electron - Fluoride ion O -2 Has gained two electrons - Oxide ion

Group 1A: Elements lose 1 electron to form +1 ions H +1 Li +1 Na +1 K +1 Rb +1

Group 2A: Lose 2 electrons to form +2 ions Be +2 Mg +2 Ca +2 Sr +2 Ba +2

Group 3A: Elements lose 3 electrons to form +3 ions Elements lose 3 electrons to form +3 ions B +3 Al +3 Ga +3

Group 4A: Do these lose 4 electrons or gain 4 electrons? Do these lose 4 electrons or gain 4 electrons? Neither! Group 4A elements rarely form ions (they tend to share e - instead)

Group 5A: These gain 3 electrons to form -3 ions These gain 3 electrons to form -3 ions N -3 P -3 As -3 Nitride Phosphide Arsenide

Group 6A: These gain 2 electrons to form -2 ions These gain 2 electrons to form -2 ions O -2 S -2 Se -2 Oxide Sulfide Selenide

Group 7A: These gain 1 electron to form -1 ions These gain 1 electron to form -1 ions F -1 Cl -1 Br -1 Fluoride Chloride Bromide I -1 Iodide

Group 8A: Stable noble gases do not form ions or share electrons! Stable noble gases do not form ions or share electrons!

Group B elements: Many transition metal elements Many transition metal elements have more than one possible ionic charge. have more than one possible ionic charge. Iron (II) = Fe +2 Iron (III) = Fe +3 Use Roman numerals to show charges

Some of the post-transition elements also Some of the post-transition elements also have more than one possible ionic charge. have more than one possible ionic charge. Tin (II) = Sn +2 Lead (II) = Pb +2 Tin (IV) = Sn +4 Lead (IV) = Pb +4

 Some ions are made of only one particle of an element.  These are monoatomic ions. (mono = “one”)  Examples: Na +1 and Cl -1  Other ions are made of more than one particle bonded together.  These are polyatomic ions. (poly = “many”)  Examples: OH -1 and PO 4 3-

CATION ANION

 These form when ions are bound together by their opposite charges.  The ionic bond forms from the chemical attraction between cations and anions.  As they say, “opposites attract!”

Indicates the relative number of atoms or polyatomic ions in a chemical compound. Examples:NaCl CaCO 3 CaBr 2 Li 2 O A formula unit is the lowest whole number ratio of ions in an ionic compound. Example: NaCl is the lowest ratio. You wouldn’t write this formula as Na 6 Cl 6.

 Compounds composed of 2 elements.  Compounds are neutral.  Elements combine in ratios to make the charges cancel out.  If the ions in the ionic compound have equal and opposite charges, the formula unit contains one of each ion. ◦ Na +1 and Cl -1 combine to form NaCl. ◦ Mg +2 and S -2 combine to form MgS.

 If the charges on the ions are NOT equal, use the crossover rule to determine the chemical formula for the compound. Ex: Al 3+ + O 2-  Crossover the charge on the aluminum ion and it becomes the subscript for the oxygen, then, crossover the charge on the oxide ion and it becomes the subscript for the aluminum ion. 24

The crossover rule still applies. Here is an example: Sn 4+ + SO 4 2- (Polyatomic ion) Use Crossover Rule : Sn 4+ (SO 4 ) Sn 2 4+ (SO 4 ) 4 2- If there is more than one polyatomic ion, place its formula in parenthesis. (Do not include the charges in your final formula.) Then, reduce the subscripts to smallest whole number. Sn 2 (SO 4 ) 4 = Sn(SO 4 ) 2 = tin(IV)sulfate