Names and Formulas of Compounds

ion An atom or bonded group of atoms that have lost or gained electrons to become charged Lose electrons= + charge Gain electrons= - charge The number of electrons lost/gained determines the charge on the ion

Monatomic ion A one atom ion

Oxidation number The charge on a monatomic ion

Valence electrons The outermost electrons that are involved in chemical bonding Group number will tell how many valence electrons, disregarding any ones in the ten’s place Ex: Group 1 has 1 valence e - Group 13 has three valence e - Group 18 has 8 valence e -

Octet Rule All atoms- except for hydrogen and helium- need 8 electrons in their outmost energy level to be stable –Hydrogen and helium need 2 electrons to be stable Atoms bond with each other to become stable Bonds can be ionic or covalent

Formation of ions Elements in groups 1-13 form positive ions –Most of the transition metals can form ions with multiple charges –Example: copper can form +1 and +2 ions Elements in group 14 can be +4 or -4 Elements in groups tend to form negative ions

Ionic Bond Forms when electrons are transferred form atom to another, creating ions Ions of opposite charge are attracted to each other and an ionic compound is formed The sum of the charges of the ions in an ionic compound must equal ZERO –For a compound formed from Cu 2+ and F -, two fluorine ions are needed to balance the copper ion charge –Ex: (2+) + (1-) + (1-) = 0

Ionic compound Compound formed by the electrostatic attraction between ions of opposite charge Ex: Na + and Cl -

Formula unit Simplest ratio of the ions in an ionic compound CuO not Cu 2 O 2

Binary compounds Made up of two ELEMENTS, not atoms

Cation and anion Cation- positive ion, usually a metal –Written first in the name and the formula –Is the element name –Roman numeral in parentheses gives the charge for elements that have more than one possible charge Anion- negative ion, a nonmetal or metalloid –Written last in the name and formula –Drop element ending and add suffix –ide –Ex: oxygen=oxide, chlorine=chloride

Writing formulas for binary ionic compounds Determine the charge on the cation Determine the charge on the anion Criss cross the numbers, NOT the + and - Write the formula: – Cation symbol first with subscripts to show how many are in the formula –Anion symbol last with subscripts to show how many are in the formula –Simplify if needed to get smallest whole number ratio

Practice Write formulas for: The compound formed from magnesium and fluorine compound formed from aluminum and oxygen

Writing formulas from names The name will tell you which elements are involved Follow the same rules already given EX: magnesium sulfide EX: sodium hydride

Practice Write formulas for each of the following ionic compounds: 1.Sodium fluoride 2.Aluminum chloride 3.Barium sulfide

Ions with multiple charges Some elements can form ions with different charges Example: copper can have +1 or +2 charge This affects the chemical formula and the properties of the compound formed Must indicate which charge is present for that ion

Ions with multiple charges Stock system –Uses parentheses and Roman numerals to indicate charge –EX: copper (I) has a 1+ charge

Writing formulas with Stock system The Stock system tells you the CHARGE of the cation inside parentheses, NOT the number of ions EX: copper (I) bromide Cu 1+ Br 1- CuBr

Polyatomic ions Ions that contain more than one element

Writing formulas with polyatomic ions The same general rules apply as with binary compounds Determine ion charges Determine how many of each ion are needed to equal zero Write cation symbol and anion symbol Place subscripts for each ion in the formula –If only one polyatomic ion is needed, no subscript –If more than one polyatomic ion is needed, place the entire polyatomic ion symbol in parentheses, then write subscript outside the parenthesis

Practice Write formulas for : 1. Potassium hydroxide 2. Calcium nitrate 3. Ammonium chlorate

Multiple charges and polyatomic ions Formulas for compounds with a cation with multiple charges and a polyatomic ion are written just like any other compound formula Determine charges on ions Write cation and anion symbols with charges Criss cross numbers Place polyatomic ion in parentheses if you have more than one in the compound’s formula

Practice Write the formula for each of the following compounds: 1.Copper (II) sulfate 2.Manganese (III) nitrate 3.Iron (II) phosphate 4.Iron (III) dichromate

Naming ionic compounds Binary compounds: –Name cation first with the element name –Name anion last. Drop the element name ending and add the suffix -ide Non-binary compounds: –Name cation first, element or polyatomic ion name –Name anion last, polyatomic ion keeps its name, monatomic ion ends in -ide

Practice Name the following compounds: 1.CaS 2.Na 3 N 3.Mg(NO 2 ) 2 4.(NH 4 ) 2 SO 4

Naming with the Stock system Names of cations with more than one charge MUST indicate which charge is on the ion by placing a Roman numeral in parentheses after the cation This Roman numeral indicates CHARGE not number of ions Example: CoCl 2 is cobalt (II) chloride

Practice Name the following using the Stock system: –Cu 2 S –CuS –Fe(NO 3 ) 2 –Fe(NO 3 ) 3