Chapter 3 Molecules Compounds and Chemical Equations Chemical Bonds o The Properties of the compound are totally different from the constituent elements o Compounds are made of atoms held together o Chemical Bonds o The bonding attraction comes from attractions between protons and electrons are forces of attraction between atoms Bonding Types o Two general types of bonding between atoms found in compounds ionic and covalent o Ionic Bonds resulting in oppositely charged ions that attract each other result when electrons have been transferred between atoms Generally found when metal atoms bond to nonmetal atoms Bonds form due to force of attraction between oppositely charged ions o Covalent Bonds Result when two atoms share some of their electrons Generally found when nonmetal atoms bond together Bonds form between atoms by sharing electrons Resulting collection of atoms is called a molecule Representing Compounds Chemical Formula and Molecular Models o Chemical Formula indicates the elements present in the compound and the relative number of atoms or ions of each o There are different types of chemical formula Empirical Formula in compound Molecular Formula in a molecule of a compound gives the relative number of atoms of each element gives the actual number of atoms of each element Ex Hydrogen Peroxide Empirical Formula HO Structural Formula atoms connection in molecular Molecular Models Ball and Stick and space filling using lines represent the covalent bonds shows Classification of Elements and Compound o Elements may be either atomic or molecular o Compounds may be either molecular o Atomic Element or ionic with single atom as its basic unit He Fe exists in nature o Molecular Compounds Exist in nature as molecules when two or atoms are o Molecular Elements bonded together nonmetals bonds Basic unit of I C is the formula unit the smallest electrically neutral collection of ions Compounds that Contain Ions Composed of two or more covalently bonded o Ionic Compounds Composed of cations and anions bounded together by ionic o Compound must have no total charge therefore we must balance the numbers of cations and anions in a compound to get 0 charge o If Na is combined with S2 you will need two Na ions for every S2 ion to balance the charges therefore the formula must be Na2S Naming Monatomic Nonmetal Anion o Determine the charge from position on the Periodic o To name anion change ending on the element to Table ide Polyatomic Ions o Polyatomic ions are single ions that contain more than one atom o Often identified by parentheses around ion in formula o Name and charge of polyatomic ion do not change o Name any ionic compound by naming cation first then anion Common Polyatomic Ions o Elements in the same column form similar polyatomic ions o If the polyatomic ion starts with H add hydrogen prefix before the name and Patterns for Polyatomic Ions add 1 to the charge Writing Formula for Ionic compounds containing polyatomic ion Iron III Phosphate o Write the Symbol for the cation and its charge o Write the symbol for the anion and its charge o Charge without sign become subscript for other ion ratio o Reduces subscripts to smallest whole number o Check the total charge of the cations cancels the total charge of anions Hydrates formula unit o Hydrates are ionic compounds containing a specific number of waters for each o Water of hydration often driven off by heating o In formula attached waters follow o In name attached waters indicated by Prefix hydrate after name of ionic compound Naming Binary Molecular o 1 Name the Element o 2 Name the Second Element with an ide o 3 Add a prefix to each name to indicate the subscript o Write the first element with prefix then the second element with prefix Drop prefix mono from first element Subscript Prefixes o 1 mono Not used on first nonmetal o 2 di o 3 tri o 4 tetra o 5 penta o 6 hexa o 7 hepta o 8 octa o 9 nona o 10 deca Acids o Contain H 1 cation and anion In aqueous solution o Binary acids have H 1 cation and nonmetal anion o Oxyacids have H cation and polyatomic anion Naming Binary Acids o 1 Identify the anion o 2 Name the anion with an ic suffix o 3 Add a hydro prefix to the anion name o 4 Add the word acid to the end Naming Oxyacids o If polyatomic ion name ends in ate then change ending to ic suffix o If polyatomic ion name ends in ite then change ending to ous suffix o Write word acid at end of all names Writing Formula for Acids o When name ends in acid formulas starts with H o Write formulas as if ionic even though it is molecular o Hydro prefix means it is binary acid no prefix means it is an oxyacid o For oxyacid if ending is ic polyatomic ion ends in ate if ending is ous polyatomic ion ends in ous Binary Acids o 1 Write the symbol for the Cation and its charge o 2 Write the symbol for the anion and its charge o 3 Charge without sign becomes subscript for other ion o 4 Add aq to indicate dissolved o 5 Check that the total charge of the cations cancels the total charge of the o The mass of an indivudal molecule or formula unit Also known as molecular mass of molecular weight o Sum of the masses of the atoms in a single molecule or formula unit anions Formula Mass Whole sum of the parts Percent Composition o Percentage of each element in a compound By mass o Can be determined from The formula of the compound The experimental mass analysis of the compound o The percentages may not always total to 100 due to rounding Mass Percent as a Conversion Factor o The mass percent tells you the mass of a constituent element in 100g of the compound The fact that CCl2F2 is 58 64 Cl by mass means that 100g of CCl2F2 contains 58 64g CL o This can be used as a conversion factor 100g CCl2F2 58 64g Cl Finding an Empirical Formula o 1 Convert the percentages to grams Assume you start with 100g of the compound Skip if already in grams o 2 Convert grams to moles Use molar mass of each element o 3 Write a pseudo formula using moles as subscripts o 4 Divide all by smallest number of moles If result is within 1 of whole number round to whole number o 5 Multiply all mole ratios by number to make all whole numbers If ratio unknown 5 multiply all by 2 if ratio 33 or 67 multiply all by 3 if ratio 25 75 multiply all by 4 Skip if already whole numbers Molecular Formulas o The molecular formula is a multiple of the empirical formula o To determine the molecular formula you need to know the empirical formula and the molar mass of the compound Combustion Analysis o