Molecules, Compounds, and Nomenclature: Study Notes

Chapter 3: Molecules, Compounds, and Nomenclature

Chapter Outline

• Compounds: Chemical Formulas and Molecular Models

• Chemical Bonds

• Formulas and Names

• Formula Mass and the Mole Concept for Compounds

• Composition of Compounds

• Determining a Chemical Formula from Experimental Data

Chemical Bonds

Types of Chemical Bonds

Chemical bonds are the forces that hold atoms together in compounds. The two main types are ionic bonds and covalent bonds.

• Ionic bond: Formed when electrons are transferred from one atom (typically a metal) to another (typically a nonmetal), resulting in oppositely charged ions that attract each other.

• Covalent bond: Formed when two nonmetal atoms share one or more pairs of electrons.

Example: Sodium chloride (NaCl) forms via ionic bonding between sodium (Na) and chlorine (Cl). Water (H2O) forms via covalent bonding between hydrogen and oxygen.

Representing Compounds: Chemical Formulas and Molecular Models

Chemical Formulas

Chemical formulas provide information about the elements present in a compound and their ratios.

• Molecular formula: Shows the actual number of atoms of each element in a molecule (e.g., H2O).

• Empirical formula: Shows the simplest whole-number ratio of atoms in a compound.

• Structural formula: Illustrates how atoms are connected using lines for chemical bonds.

• For ions: The charge is shown as a superscript (e.g., Na+, Cl-).

• Subscripts: Indicate the number of atoms of each element. The number 1 is always omitted.

Example: In H2O, the subscript '2' indicates two hydrogen atoms; oxygen has no subscript, meaning one atom.

Molecular Models

Molecular models help visualize the structure and geometry of molecules. Common types include:

• Structural formula: Shows connectivity of atoms (e.g., H–O–H for water).

• Ball-and-stick model: Represents atoms as balls and bonds as sticks, showing angles and connectivity.

• Space-filling model: Shows the relative sizes of atoms and how they fill space in a molecule.

Compound	Molecular Formula	Structural Formula	Ball-and-Stick Model	Space-Filling Model
Methane	CH4	Shows tetrahedral geometry	Atoms as balls, bonds as sticks	Atoms as spheres touching each other
Ethene	C2H4	Double bond between carbons	Planar structure	Atoms fill space
Glucose	C6H12O6	Ring structure with hydroxyl groups	Complex 3D arrangement	Shows molecular volume
Water	H2O	Bent structure	Angle between H–O–H	Atoms overlap

Additional info: The models are essential for understanding molecular geometry, polarity, and reactivity.