Covalent molecules share electrons.  there is generally no order to the formation of covalent molecules  these molecules clump together as solids, liquids or gases 4.2 – Names and Formulae of Compounds Ionic compounds are made up of +ve and -ve ions.  the ions are well-ordered at the atomic level  -ve – +ve ________________  -ve – -ve and +ve – +ve ____________  Ionic compounds form from the inside-out as solid crystals. NaCl H2OH2O

Cross Rule for Writing Formulae of Ionic Compounds Examples where you can reduce:

The Chemical Name of an Ionic Compound Al 2 O 3 non-metal ion 2 nd metal ion named 1 st subscripts indicate lowest* whole # ratio of ions in compound (*reduce subscripts by GCF, if necessary)

The Chemical Name of an Ionic Compound The name of an ionic compound: cation + anion-ide  Ex. Name the ionic compound that forms between magnesium and oxygen  the cation is:  the anion is:  the name of the ionic compound is: Ex. Name the following ionic compounds: a)Ca 3 N 2 _______________________________ b)SrS_______________________________ c)LiCl_______________________________

The Chemical Formula of an Ionic Compound Writing formulas for ionic compounds.  In an ionic compound, the totals of the +ve and –ve ion charges must equal zero so that the compound is _________________  Ex. Using the cross rule, write the chemical formula for: a)magnesium phosphide a)calcium oxide a)zirconium sulphide

Formula of an Ionic Compound with a Multivalent Metal Recall: On the PT, the most common form of the ion of a multivalent metal is listed first.  In the name of the compound, a roman numeral is used following the cation to indicate which ion was used. Ex. a)Write the chemical formula for manganese (III) sulphide b) Use the reverse cross rule to name the ionic compounds:  SnCl 4  CrF 2  CrF 3  Au 3 N  AuN

FYI… Another Naming System for Ionic Compounds with Multivalent Metals Instead of using roman numerals to specify the combining capacity of a multivalent metal that has 2 combining capacities, a suffix system may be used.  the ion with the lesser charge ends with –ous  the ion with the greater charge ends with –ic ElementCatio n Systematic NameOld Style Name CopperCu 1+ Cu 2+ IronFe 2+ Fe 3+ LeadPb 2+ Pb 4+ TinSn 2+ Sn 4+

FYI… Another Naming System for Ionic Compounds with Multivalent Metals Ex. Name the ionic compounds using the “old” naming system: 1.SnCl 4 2.CuF 3.FeN 4.PbO

Polyatomic Ions …consist of ≥ 2 types of atoms joined together by covalent bonds.  the whole group carries a +ve or –ve electric charge, therefore forms ionic bonds  Ex. What is the formula for sodium sulphate?  Ex. What is the name of the compound KClO?

Polyatomic Ions Ex. Write the chemical formulae for the following compounds: a)calcium nitrate b)aluminum hydroxide c)barium sulphite d)lithium chromate e)ammonium nitrite

Names and Formulae of Covalent Compounds Covalent compounds, also called molecules, rely on the chemical formula to reveal the components of the molecule.  Covalent compounds are made up of two or more non-metals.  **Note:  In an ionic compound, subscripts show smallest whole- number ratio of ions in the compound.  In a covalent compound, subscripts show the actual number of atoms in the molecule.  Ex. Write the chemical formula for the following covalent molecules: a)glucose b)water c)hydrogen peroxide

Naming Binary Covalent Compounds Binary covalent compounds (2 non-metal atoms joined by ≥ 1 covalent bond) use a system of prefixes in naming (different rules apply if the compound starts with H)  Prefixes are used before* the name of the element to indicate the number of atoms in the molecule  *if there is only 1 atom of the 1 st element, do not use the prefix “mono-”  CO is carbon monoxide (not “monocarbon monoxide”)  CO 2 is carbon dioxide  Write the “most metallic” (furthest left) element 1 st  Add -ide to end of the second element’s name

Writing Formulae for Binary Covalent Compounds Ex. Write the chemical formula for: a) trinitrogen tetrachloride b) tetraphosphorous decaoxide c) diphosphorus pentasulphide d) nitrogen monoxide e) carbon tetraiodide f) nitrogen trifluoride g) dinitrogen tetroxide h) silicon disulphide

Naming Binary Covalent Compounds Ex. Name the following covalent compounds: a) Si 3 P 6 a) CCl 4 b) CS 2 c) PBr 3 d) P 2 O 3 e) N 2 O

Comparing Ionic and Covalent Compounds To determine whether a compound is ionic or covalent… 1.Examine the formula ionic compounds start with a metal / the ammonium ion covalent compounds start with a non-metal 2.If the compound is covalent… and binary (and does not start with hydrogen), use the prefix system if there are more than 2 different elements (or it starts with H), there is probably a simpler name for the covalent molecule 3.If the compound is ionic… check to see if the metal is multivalent (add a roman numeral if it is) the metal ion is named first if it ends with a single non-metal, naming will just end in –ide if it ends in a polyatomic ion, look up its name / formula

Polar Molecules …are molecules in which electrons are attracted more strongly by one type of atom than another. because of unequal sharing of electrons, polar molecules have a slightly +ve end and a slightly –ve end Ex. in a covalently bonded molecule of HF, the F atom attracts e -s more strongly than the H atom does  there is a slightly +ve charge near the ________ end and a slightly –ve charge near the ________ end of the HF molecule Do Practice Problems on p