1. Chemical Compounds and Ionic review

2. Formulas Chemical formula- the kind and number of atoms in the smallest unit of the substance If the molecules of the element each have more than 1 atom, a number is used as a subscript Molecular formula- shows the kinds and numbers of atoms present in a molecule of a compound Remember that a subscript written after the symbol indicates the number of atoms of each element, if there is one only element the 1 subscript is omitted Formula units- they represent ionic compounds; the lowest whole number ratio of ions in the compound

3. The law of Definite and Multiple Proportions Law of definite proportions- the masses of elements in a compound will always stay in the same proportions in a sample Atoms combine in whole number ratios To solve- take compound A and reduce, then reduce compound B; compare masses of element x to element y by dividing masses Law of multiple proportions- whenever 2 elements form more than 1 compound, the different masses of 1 element that combine with the same mass of the other element are in the ratio of small whole numbers

4. Ions Monatomic ions- ions consisting of 1 atom Remember that metallic elements lose electrons (cations) Group # tells you their charge. Aluminum is the only group 3 ion (Al 3+ ) Nonmetallic elements gain electrons (anions) Subtract the group number from 8 to give charge 3 nonmetals in group 5A form anions Groups 4A and 8A do not usually form ions Many of the transitions metals have more than one common ionic charge Stock name is preferred Roman numeral in () tells ionic charge

5. exceptions Transition metal exceptions- Silver (Ag + ) Cadium and zinc (Cd 2+ and Zn 2+ )

6. Polyatomic ions Tightly bound groups of atoms that behave as a unit and carry a charge Names of most of the polyatomic ions end in –ite or –ate 3 exceptions- ammonium (NH 4+ ), cynide (CN - ), hydroxide (OH - ) -ite ending tells that there is 1 LESS oxygen then the –ate When the polyatomic ion begins with a hydrogen; it carries a + charge, the polyatomic ion carries a – charge. When the ion forms the net charge is 1 less then the ion charge