Objectives To describe the formation of ions from their parent atoms To learn to name ions To predict which ion a given element forms by using the periodic table To describe how ions combine to form neutral compounds

+ What is the total of all the ‘+’ and ‘-’ ? - 4+ 4- - + The total charge is zero. This is a neutral atom. All atoms start out neutral. - -

+ What is the total if the atom loses an electron? - 4+ 3- - 1+ The total charge is 1+. This is a positive ion. Losing electrons makes the atom more positive. - -

+ What is the total if the atom gains an electron? - - 4+ 5- - 1- The total charge is 1-. This is a negative ion. Gaining electrons makes the atom more negative. - -

A. Ions Atoms can form ions by gaining or losing electrons. Metals tend to lose one or more electrons to form positive ions called cations. Cations are generally named by using the name of the parent atom.

A. Ions Nonmetals tend to gain one or more electrons to form negative ions called anions. Anions are named by using the root of the atom name followed by the suffix –ide.

A. Ions Ion Charges and the Periodic Table The ion that a particular atom will form can be predicted from the periodic table. The most predictable are: Elements in Group 1 (alkali metals) form 1+ ions Elements in Group 2 (alkaline earth metals) form 2+ ions Aluminum family metals form 3+ ions Group 7 (halogens) form 1- ions Group 6 (oxygen family) form 2- ions

A. Ions Ion Charges and the Periodic Table

B. Compounds That Contain Ions Ions combine to form ionic compounds. Properties of ionic compounds High melting points Conduct electricity if ions can move: If melted If dissolved in water

B. Compounds That Contain Ions Ionic compounds are electrically neutral. The charges on the anions and cations in the compound must sum to zero. Would these charge combinations work? +2 -1 +1 +1 -2 +2 -1 -1 -1 +3 +3 -2 -2 -2 = +1 NO – not neutral = 0 YES = -1 NO – not neutral = 0 YES

B. Compounds That Contain Ions Formulas for Ionic compounds Write the cation element symbol followed by the anion element symbol. (positive attitude goes first!) The number of cations and anions must be correct for their charges to sum to zero.

Predict the ion formed by each element. Sodium Magnesium Fluorine Bromine Oxygen Calcium Aluminum Lithium Chlorine Na+ Mg2+ F- Br - O2- Ca2+ Al3+ Li+ Cl-

Make the correct formulas from the ions below. K+ and Cl- Ba2+ and I- Ga3+ and Br- Sr2+ and O2- Li+ and S2- Al3+ and N3- Cr3+ and O2- KCl (1+ 1-) BaI2 (2+ 1-1-) GaBr3 (3+ 1-1-1-) SrO Li2S AlN Cr2O3

Make the correct formula for each pair of elements. Magnesium and chlorine Bromine and aluminum Calcium and nitrogen Mg2+ Cl- Cl-  MgCl2 Positive goes first Br - Br - Br - Al3+  AlBr3 Ca2+ Ca2+ Ca2+ N3- N3-  Ca3N2