Molecules and Ions Image courtesy of www.lab-initio.com

Molecules Two or more atoms of the same or different elements, covalently bonded together. Molecules are discrete structures, and their formulas represent each atom present in the molecule. Pentane, C5H12

Covalent Network Substances Covalent network substances have covalently bonded atoms, but do not have discrete formulas. Why Not?? Graphene – carbon allotrope

Ions Cation: A positive ion Mg2+, NH4+ Anion: A negative ion Cl−, SO42− Ionic Bonding: Force of attraction between oppositely charged ions. Ionic compounds form crystals, so their formulas are written empirically (lowest whole number ratio of ions).

Predicting Ionic Charges Group 1: Lose 1 electron to form 1+ ions H+ Li+ Na+ K+ Rb+ Cs+

Predicting Ionic Charges Group 2: Loses 2 electrons to form 2+ ions Be2+ Mg2+ Ca2+ Sr2+ Ba2+

Predicting Ionic Charges Group 13: Loses 3 electrons to form 3+ ions B3+ Al3+ Ga3+

Predicting Ionic Charges Loses 4 electrons or gains 4 electrons Group 14: Caution! C22- and C4- are both called carbide

Predicting Ionic Charges Nitride Gains 3 electrons to form 3- ions Group 15: Phosphide P3- As3- Arsenide

Predicting Ionic Charges Oxide Group 16: Gains 2 electrons to form 2- ions S2- Sulfide Se2- Selenide

Predicting Ionic Charges Group 17: Gains 1 electron to form 1- ions F1- Fluoride Cl1- Chloride Br1- Bromide I1- Iodide

Predicting Ionic Charges Group 18: Stable Noble gases do not form ions!

Predicting Ionic Charges Groups 3 - 12: Many transition metals have more than one possible oxidation state. Iron(II) = Fe2+ Iron(III) = Fe3+

Predicting Ionic Charges Groups 3 - 12: Some transition metals have only one possible oxidation state. Zinc = Zn2+ Silver = Ag+

Writing Ionic Compound Formulas Example: Barium nitrate 1. Write the formulas for the cation and anion, including CHARGES! 2. Check to see if charges are balanced. 3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. Ba2+ ( ) NO3- 2 Not balanced

Writing Ionic Compound Formulas Example: Ammonium sulfate 1. Write the formulas for the cation and anion, including CHARGES! 2. Check to see if charges are balanced. 3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. ( ) NH4+ SO42- 2 Not balanced

Writing Ionic Compound Formulas Example: Iron(III) chloride 1. Write the formulas for the cation and anion, including CHARGES! 2. Check to see if charges are balanced. 3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. Fe3+ Cl- 3 Not balanced

Writing Ionic Compound Formulas Example: Aluminum sulfide 1. Write the formulas for the cation and anion, including CHARGES! 2. Check to see if charges are balanced. 3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. Al3+ S2- 2 3 Not balanced

Writing Ionic Compound Formulas Example: Magnesium carbonate 1. Write the formulas for the cation and anion, including CHARGES! 2. Check to see if charges are balanced. Mg2+ CO32- They are balanced

Writing Ionic Compound Formulas Example: Zinc hydroxide 1. Write the formulas for the cation and anion, including CHARGES! 2. Check to see if charges are balanced. 3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. ( ) Zn2+ OH- 2 Not balanced

Writing Ionic Compound Formulas Example: Aluminum phosphate 1. Write the formulas for the cation and anion, including CHARGES! 2. Check to see if charges are balanced. Al3+ PO43- They ARE balanced

Naming Ionic Compounds Cation first, then anion Monatomic cation = name of the element Ca2+ = calcium ion Monatomic anion = root + -ide Cl− = chloride CaCl2 = calcium chloride

Naming Ionic Compounds Metals with multiple oxidation states some metal forms more than one cation use Roman numeral in name PbCl2 Pb2+ is cation PbCl2 = lead(II) chloride

Binary Molecular Compounds Compounds between two nonmetals First element in the formula is named first. Keeps its element name Gets a prefix if there is a subscript on it Second element is named second Use the root of the element name plus the -ide suffix Always use a prefix on the second element

List of Prefixes 1 = mon(o) 2 = di 3 = tri 4 = tetra 5 = penta 6 = hexa 7 = hepta 8 = octa 9 = nona 10 = deka List of Prefixes

Naming Binary Compounds diphosphorus pentoxide CO2 = carbon dioxide CO = carbon monoxide N2O = dinitrogen monoxide

Practice – Write the Formula Compound Name Compound Formula Carbon dioxide Carbon monoxide Diphosphorus pentoxide Dinitrogen monoxide Silicon dioxide Carbon tetrabromide Sulfur dioxide Phosphorus pentabromide Iodine trichloride Nitrogen triiodide Dinitrogen trioxide Check next slide for answers

Answers – Write the Formula Compound Name Compound Formula Carbon dioxide CO2 Carbon monoxide CO Diphosphorus pentoxide P2O5 Dinitrogen monoxide N2O Silicon dioxide SiO2 Carbon tetrabromide CBr4 Sulfur dioxide SO2 Phosphorus pentabromide PBr5 Iodine trichloride ICl3 Nitrogen triiodide NI3 Dinitrogen trioxide N2O3

Practice – Name the Compounds Compound Formula Compound Name N2O4 SO3 NO NO2 As2O5 PCl3 CCl4 H2O SeF6 Check next slide for answers

Answers – Name the Compounds Compound Formula Compound Name N2O4 dinitrogen tetroxide SO3 sulfur trioxide NO nitrogen monoxide NO2 nitrogen dioxide As2O5 diarsenic pentoxide PCl3 phosphorus trichloride CCl4 carbon tetrachloride H2O dinitrogen monoxide SeF6 selenium hexafluoride