Chemical Formulas and Chemical Compounds Chapter 7

Molecular and Ionic Compounds Molecular Compound (Covalent) Composition metal-nonmetal nonmetal-nonmetal Smallest unit formula unit molecule Smallest particles ions atoms

Significance of Chemical Formulas Subscripts—refer only to the atom (or atoms in parentheses) that come BEFORE it Al2(SO4)3 NOTE: multiply subscripts outside parentheses with the subscripts inside them to get the total number of each atom

Naming Monatomic Ions Monatomic: made up of only ONE atom All group A (main group) monatomic CATIONS: simply name the name of the element and add “ion” to it All monatomic anions: change ENDING to “-ide” (NOTE: most elements lose a significant amount of their name. Ex. sulfur  sulfide; phosphorus phosphide; oxygen  oxide)

Naming Monatomic Ions Cont… Stock System: uses roman numerals to indicate the positive charge an ion has Copper (II) means Cu+2 USE THIS SYSTEM ONLY WHEN NAMING TRANSITION METAL IONS Exceptions: Tin (Sn) and Lead (Pb) also get the roman numeral

Naming Monatomic Ions Cont… Name Stock System Fe2+ ferrous iron(II) Fe3+ ferric iron(III) Ag1+ silver Silver(I) Pb2+ plumbous lead(II) Pb4+ plumbic lead(IV)

Polyatomic Ions Some Transition Metal naming rules: “ic” ions have a greater (+) charge than “ous” ions Ex. ferric (Fe3+) and ferrous (Fe2+) Polyatomic ions—made up of two or more atoms (charge applies to the entire species) for anions: hypo-anion-ite < anion-ite < anion-ate < per-anion-ate in terms of O’s in the ion (all will have the same NEGATIVE charge) Ex. ClO- ClO2- ClO3- ClO4- NOTE: not all “ate” ions will have “ite” ions

Writing formulas for Ionic Compounds If you are given the name of an ionic compound, you need to follow these rules in order to write its formula: 1. Write out the formula (with charge) of the cation (first name) 2. Write out the formula (with charge) of the anion (second name) 3. The positive charges must cancel out the negative charges (criss-cross the charges) 4. The formula must show the LOWEST whole-number ratio of cations to anions. ** You CANNOT change the formula of POLYATOMIC IONS

Rules for Ionic Formulas All Ionic Compounds are Neutral This means the total Charge must be ZERO CATIONS + ANIONS = ZERO All Ionic Compounds start with the cation (Positive Ion) first. All Ionic Compounds are in their lowest whole number ratio.

Example… Na2O Na+1 O-2 Identify the symbol for each element Find the charge for each based on group Criss – Cross the number without the charge Check to make sure all rules have been followed Sodium and Oxygen Na O Na+1 O-2 Na2O

Example

More Examples Calcium and Chlorine Aluminum and Sulfur Gallium and Phosphate

Nomenclature for Ionic Compounds To name an ionic compound: * Identify the compound as ionic (m-nm or polyatomic ion present) * Identify the cation (first ion). Ignore how many are present. *Identify the anion (second ion). Ignore how many are present. * You MUST be able to recognize polyatomic ions by sight. * Name is: cation anion If the cation is a TRANSITION METAL you will need a roman numeral

The name must identify which ion it is, because transition metals have multiple Oxidation Numbers (Charges) Name is: cation ( ) anion *Work backwards to figure out the charge.