Ions, Valences and Oxidation Numbers

Formation of ions from atoms X X + sodium ion 11Na+ 2, 8 one electron transferred X 17Cl- 2, 8, 8 X - chloride ion sodium atom X chlorine atom 11Na 2, 8, 1 17Cl 2, 8, 7

Rule of Octet An atom is most stable when it’s outer e- shell is filled (except for H which is 2, that number is 8) Valence e- are the # of e- in the outer shell. In the main groups, the valence # is the last digit of the group. Oxidation # can refer to a couple of things: a. The charge of a monoatomic ion b. In a molecule or polyatomic ion the oxidation # is the value of a “pseudo-charge”

A polyatomic ion (list on pg 268): A monoatomic ion: Na has only 1 valence e-, when it becomes an ion its oxidation number is +1 because it loses that ion. Oxidation value of these tend to be constant and are formed according to the rule of octet. A polyatomic ion (list on pg 268): Is an ion like NO3- or PO4-3; they don’t split up very easily/are involved in chemical reactions as a unit. Compounds have oxidation values of 0 because the individual ion charges have cancelled out.

Formation of positive ion from its atom X + sodium ion 11Na+ 2, 8 sodium atom X 11Na 2, 8, 1

Formation of positive ion from its atom X + X sodium atom loses one electron to form sodium ion with 1+ charge 11Na+ 2, 8 by losing an electron from its outer energy shell 11Na 2, 8, 1

Formation of negative ion from its atom X 17Cl- 2, 8, 8 X - chloride ion chlorine atom 17Cl 2, 8, 7

Formation of negative ion from its atom X X - chlorine atom gains one electron to form chloride ion with 1- charge by gaining an electron in its outer energy shell 17Cl 2, 8, 7 17Cl- 2, 8, 8

Lewis Dot Structures Lewis Dot structures are used to symbolize the location of electrons in the outermost energy level. These are useful in determining how an atom will bond. Each electron is represented with a dot around the symbol of the element. Each element can have a maximum of 8 electrons around it.

Practice examples