2/1/2011 1 Topics: Bonds Nomenclature (formula to name and back again) Mass/Formula/Mole Relationships (Includes mass %) Empirical & Molecular Formula/Data Relationships Writing/Balancing Chemical Equations Chapter Chapter 3 Molecules, Compounds, & Chemical Equations Chemical Bonds & Types • Two general types of bonding between atoms found in compounds are ionic and covalent • Ionic bonds result when electrons have been transferred between atoms, resulting in oppositely charged ions that attract each other (e.g., metal & non-metal ions) • Covalent bonds result when two atoms share some of their electrons (e.g., when nonmetal atoms bond together) 2 Tro: Chemistry: A Molecular Approach, 2/e • Chemical bonds are forces of attraction between atoms • The bonding attraction comes from attractions between protons and electrons
2/1/2011 2 Elements and Compounds • Elements combine together to make an almost limitless number of compounds • The properties of the compound are totally different from the constituent elements Example: Water Hydrogen Oxygen bp 100 °C -253 °C -183 °C state (RT) liquid gas gas flammability used to explosive needed for extinguish combustion flame 3 Tro: Chemistry: A Molecular Approach, 2/e Formulas Describe Compounds • A compound is a distinct substance that is composed of atoms of two or more elements • Describe the compound by describing the number and type of each atom in the simplest unit of the compound. (The simplest unit may be a molecule or ions.) • Each element is represented by its letter symbol • The number of atoms of each element is written to the right of the element as a subscript head2right if there is only one atom, the 1 subscript is not written • Polyatomic ions are placed in parentheses if there is more than one Ion the simplest unit of the compound 4 Tro: Chemistry: A Molecular Approach, 2/e
2/1/2011 3 Representing Compounds with Chemical Formula and Models • Compounds are generally represented with a chemical formula or model ; each type is slightly different • All chemical formulas and models tell what elements are in the compound 5 Tro: Chemistry: A Molecular Approach, 2/e Types of Formulas: Empirical Formula • An empirical formula gives the relative number of atoms of each element in a compound • The formulas for ionic compounds are empirical The empirical formula for the ionic compound fluorspar is CaCl 2 . This means that there is 1 Ca 2+ ion for every 2 Cl − ions in the compound. The empirical formula for the molecular compound oxalic acid is CHO 2 . This means that there is 1 C atom and 1 H atom for every 2 O atoms in the molecule. The actual molecular formula is C 2 H 2 O 4. 6 Tro: Chemistry: A Molecular Approach, 2/e
2/1/2011 4 Types of Formulas: Molecular Formula • A molecular formula gives the actual number of atoms of each element in a molecule of a compound.