CHEM 1211K 1st Edition Lecture 6 Outline of Last Lecture I Chapter 2 Atoms and Elements Continued Chapter 3 Molecules Compound and Chemical Equations II 3 4 An Atomic Level View of Elements and Compounds 1 Atomic elements exist in single atoms as basic units 2 Molecular elements exist as molecules two or more atoms as basic units Two atoms diatomic molecule more than two polyatomic molecule 3 Molecular compounds two or more covalently bonded nonmetals 4 Ionic compounds cation metals and anion nonmetals bound by ionic bonds III 1 3 2 Chemical Bonds Compounds are made of atoms held together by bonds Chemical bonds are forces of attraction between atoms Two general types of bonding between atoms found in compounds ionic and covalent Ionic bonds result when electrons have been transferred between atoms resulting in oppositely charged ions that attract each other electrostatic forces Generally found when metal atoms bond to nonmetal atoms NaCl Covalent bonds result when two atoms share some of their electrons Generally found when nonmetal atoms bond together H 2O CO IV 3 3 Representing Compounds Compounds are generally represented with a chemical formula All chemical formulas tell what elements are in the compound Use the letter symbol of the element The number of atoms of each element is written to the right of the element as a subscript if only one atom the 1 subscript is not written CO2 Na2 S N2O5 Polyatomic ions are placed in parentheses if more than one Example Sulfate ion SO42 is a polyatomic ion Types of chemical formulas 1 Empirical formula These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute The relative number of atoms of each element in a compound it does not describe how many atoms the order of attachment or the shape the formulas for ionic compounds are empirical 2 Molecular formula A molecular formula gives the actual number of atoms of each element in a molecule of a compound it does not describe the order of attachment or the shape 3 Structural formula A structural formula uses lines to represent covalent bonds and shows how atoms in a molecule are connected or bonded to each other it does not directly describe the 3 dimensional shape but an experienced chemist can make a good guess at it each line describes the number of electrons shared by the bonded atoms single line two shared electrons a single covalent bond double line four shared electrons a double covalent bond triple line six shared electrons a triple covalent bond V 3 5 Ionic Compounds Formulas and Names 1 Write the symbol for the metal cation and its charge 2 Write the symbol for the nonmetal anion and its charge 3 Charge without sign becomes subscript for other ion 4 Reduce subscripts to smallest whole number ratio 5 Check that the sum of the charges of the cations cancels the sum of the anions 6 Write systematic name by simply naming the ions a if cation is i metal with invariant charge metal name ii metal with variable charge metal name charge iii polyatomic ion name of polyatomic ion b if anion is i nonmetal stem of nonmetal name ide ii polyatomic ion name of polyatomic ion VI 3 6 Molecular Compounds Formulas and Names Molecular compounds form between two or more NONMETALS 1 Write name of first element in formula i element furthest left and down on the Periodic Table ii use the full name of the element iii Writes name the second element in the formula with an ide suffix just like for the anions however remember these compounds do not contain ions 2 Use a prefix in front of each name to indicate the number of atoms i Never use the prefix mono on the first element Current Lecture