IONIC COMPOUNDS Ionic Compounds: Form when metals and nonmetals combine by transferring electrons Metal atoms lose electrons to form positive ions Nonmetal atoms gain electrons to form negative ions Electrons are transferred from metal to nonmetal, and the resulting charged particles (ions) form an IONIC BOND Ionic Charges Determined by the number of electrons in the outermost “shell” – VALENCE Eg. Aluminum: Al has 13 protons, 13 electrons (2 in first shell, 8 in second, 3 in third) Al will lose the 3 electrons in the outermost shell and therefore has a valence of 3 Formulas for Ionic Compounds: Eg. Calcium iodide Write the symbols for elements: Ca I Write the ionic charges: Ca 2+ I 1 Select the number of ions to balance the charge CaI2 Criss-Cross Rule Calcium Iodide 2+ 1- Ca I Nickel and Oxygen Write chemical symbols: Ni O Determine valence or ionic charges Ni2+ O 2 Use criss cross rule: 2+ 2- Ni O Write formula: Ni2O2 Reduce formula: NiO POLYATOMIC COMPOUNDS Pure substances involving combinations of metals and polyatomic ions POLYATOMIC IONS are groups of atoms that tend to stay together and carry an overall ionic charge Eg. Nitrate NO3 Eg. Sulfate SO42- Formulas for polyatomic compounds: Eg. What is the formula for the ionic compound formed by sodium and a hydroxide ion? WRITE THE SYMBOLS FOR THE IONS: Na OH WRITE THE CHARGES ABOVE EACH: 1+ 1Na OH CRISS CROSS CHARGES AND SYMBOLS WRITE THE FORMULA: NaOH Naming polyatomic compounds: Combination of the metal and the name of the polyatomic ion Eg. NaOH sodium hydroxide Determine the formula and name the compound formed by combining calcium and carbonate ion. 2+ Ca 2- CO3 - CaCO3 Calcium carbonate MOLECULAR COMPOUNDS Most of the compounds you encounter everyday do not contain ions. Instead they contain molecules which share electrons to form stable arrangements. This sharing of electrons is called a covalent bond. Many nonmetals form covalent bonds. Diatomic Molecules Certain elements such as oxygen exist as covelently bonded molecules. The table on p. 202 of your text lists the elements that form diatomic molecules. Copy the information into your notes. Prefixes in Molecular Compounds Prefix mon(o)ditritetrapent(a)- Number 1 2 3 4 5 Example CO CS2 SO3 CF4 PBr5 Formulas for molecular compounds: • E.g. What is the formula for a compound formed between carbon and sulfur? • Write the symbols and their combining capacities. Write the one with the larger combining capacity first: 4 2 C S • Criss cross combining capacities to produce subscripts: C2S4 • Reduce the subscripts if possible: CS2 Naming Molecular Compounds: Molecular compounds containing hydrogen are named as if they were ionic compounds. eg. H2S hydrogen sulfide Others have common names such as water (H2O), ammonia (NH3), or methane (CH4). In general, prefixes are used to count the number of atoms when the same two elements form different combinations. IF there is only one atom of the first element, the prefix “mono” is not used. eg. CO Carbon monoxide eg. CO2 Carbon dioxide