Molecules, Compounds, and Nomenclature: Study Notes for General Chemistry

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 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 of chemical bonds are ionic bonds and covalent bonds.

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

• Covalent bond: A chemical bond formed by the sharing of electrons between two nonmetal atoms.

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 are symbolic representations of the elements in a compound and the ratios in which they combine.

• Elemental symbol: Represents each element present in the compound (e.g., H for hydrogen, O for oxygen).

• Subscript: Indicates the number of atoms of each element in the compound. If only one atom is present, the subscript is omitted.

• Charge (for ions): Shown as a superscript (e.g., Na+).

Example: In H2O, the subscript '2' indicates two hydrogen atoms for every one oxygen atom.

Types of Chemical Formulas

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

• Molecular formula: Shows the actual number of atoms of each element in a molecule.

• Structural formula: Shows how atoms are connected using lines to represent chemical bonds.

Example: The empirical formula for glucose is CH2O, while its molecular formula is C6H12O6.

Molecular Models

Molecular models help visualize the three-dimensional arrangement of atoms in a molecule.

• Ball-and-stick model: Atoms are represented by balls and bonds by sticks.

• Space-filling model: Atoms are shown as spheres that fill the space between them, representing the actual size of atoms.

Molecular Formula	Structural Formula	Ball-and-Stick Model	Space-Filling Model
CH4	H | C—H | H	[Ball-and-stick image]	[Space-filling image]
C2H2	H—C≡C—H	[Ball-and-stick image]	[Space-filling image]
C2H6O2	HO—CH2—CH2—OH	[Ball-and-stick image]	[Space-filling image]
H2O	H—O—H	[Ball-and-stick image]	[Space-filling image]

Additional info: Images referenced above are typically used in textbooks to illustrate molecular geometry and bonding, but are described here for clarity.