I. Formulas a)Chemical Formula: represents the type and number of element(s) in a chemical compound. The type of element is represented by its chemical symbol. The type of element is represented by its chemical symbol. The number of atoms of the element in the compound is represented by its subscript.The number of atoms of the element in the compound is represented by its subscript. Li 3 PO 4 Lithium = Li Phosphorus = P Oxygen = O 3 atoms 1 atoms 4 atoms NOTE: Subscripts are the numbers found to the lower right of a given chemical symbol. If a subscript is not present assume that it is a number one.

Types of Formulas 1.Molecular Formulas Represents the type and number of elements in a covalent compound.Represents the type and number of elements in a covalent compound. The subscripts do not need to be reduced in a molecular formula.The subscripts do not need to be reduced in a molecular formula. Ex: C 2 H 4 Ethene C 6 H 12 O 6 Glucose C 6 H 12 O 6 Glucose

2. Empirical Formulas Represents the lowest whole number ratio of atoms in a compound. Represents the lowest whole number ratio of atoms in a compound. For ionic compounds, the formula is always empirical. This is due to the fact that one must reduce the subscripts in an ionic compound to the lowest whole number ratio. For ionic compounds, the formula is always empirical. This is due to the fact that one must reduce the subscripts in an ionic compound to the lowest whole number ratio. Ex: Calcium Sulfide Ca S Ca +2 S -2 Ca 2 S 2 Crisscross Method Disregard the signs. Ca S Reduce

For covalent compounds (molecules), reducing its molecular formula to an empirical formula only shows the ratio of elements within the compound. For covalent compounds (molecules), reducing its molecular formula to an empirical formula only shows the ratio of elements within the compound. Ex: C 6 H 12 O 6 Molecular Formula C 1 H 2 O 1 Empirical Formula Ratio: C:H:O = 1:2:1

H2OH2OH2OH2O Molecular and Empirical Formula

3. Structural Formulas Structural formulas indicate the type, number, and arrangement of atoms within a compound. Structural formulas indicate the type, number, and arrangement of atoms within a compound. O H H O = C = O [Na] + [Cl] -

Glucose

II. Formula Writing a) Ionic compounds: Given the name of the compound: 1. Determine if the compound is binary or ternary. 2. If the compound is binary, write out the symbols for the two elements present: metal then non-metal. * Elements with lower electronegativity values are usually listed first in a chemical formula. 3. Find and write out the oxidation number for the metal and non-metal. 4. Perform the crisscross method to determine the subscripts. * Eliminate the signs from the subscripts and if necessary reduce the subscripts to the lower whole number.

5.If the compound is ternary, refers to Reference Table E. 6.Write out the symbol for the metal and the polyatomic ion. 7.Place parenthesis around the polyatomic ion. 8.Write in the oxidation number for the metal and the ionic charge of the polyatomic ion. 9. Perform the crisscross method to determine the subscripts. * Eliminate the signs from the subscripts and if necessary reduce the subscripts to the lower whole number.

Naming Ionic Compounds with a Transition Metals Elements that can have more than one possible charge MUST have a Roman Numeral to indicate the charge on the individual ion. Example #1 : Copper (II) SulfateCuSO 4 Copper’s oxidation number is +2. Sulfate’s charge is -2. Sulfate’s charge is -2. The Roman Numeral “ II ” indicates the oxidation number of the transition metal. Example #2: Iron (III) OxideFe 2 O 3 Iron’s oxidation number is +3. Oxygen’s oxidation number is -2. Oxygen’s oxidation number is -2. The Roman Numeral “III” indicates the oxidation number of the transition metal.

Examples of Older Names of Cations formed from Transition Metals

Complete the names of the following binary compounds with variable metal ions: FeBr 2 iron (_____) bromide CuClcopper (_____) chloride SnO 2 ___(_____ ) ______________ Fe 2 O 3 ________________________ Hg 2 S________________________

Complete the formulas of the following ternary compounds with variable metal ions: 1. copper(II) nitrate 2.Iron (III) hydroxide 3. Tin(IV) hydroxide

b) Covalent Compounds (molecular substances) Prefix System (binary compounds) 1. 1.Less electronegative non-metal comes first. 2. Add prefixes to indicate # of atoms. Omit mono- prefix on the FIRST element. Mono- is OPTIONAL on the SECOND element. 3. Change the ending of the second element to -ide.

Greek Numerical Prefixes 1 mono 2 di 3 tri 4 tetra 5 penta 6 hexa 7 hepta 8 octa 9 nona 10 deca

Given the names of the following molecules, determine their formulas. Dinitrogen monoxide Potassium sulfide Dichlorine heptoxide Iodine monochloride

Given the formulas of the following molecules, determine their names. BaI 2 P4S3P4S3P4S3P4S3 I2O5I2O5I2O5I2O5 CS 2 B 2 Cl 4