Bonding, Molecular Structure, and Shapes: General Chemistry Chapters 7-8 Study Guide

Chemical Bonds and Molecular Compounds

Types of Chemical Bonds

Chemical bonds are the forces that hold atoms together in compounds. Understanding the differences between ionic and covalent bonds is fundamental in chemistry.

• Ionic Bonds: Formed by the transfer of electrons between metals and nonmetals, resulting in oppositely charged ions that attract each other.

• Covalent Bonds: Formed by the sharing of electrons between nonmetal atoms.

• Example: NaCl (ionic), H2O (covalent)

Molecules vs. Compounds

Molecules are groups of atoms bonded together, while compounds are substances composed of two or more different elements chemically combined in fixed proportions.

• Molecule: May consist of a single element (e.g., O2).

• Compound: Must contain different elements (e.g., H2O).

Molecular and Empirical Formulas

Formulas represent the composition of molecules and compounds.

• Molecular Formula: Shows the exact number of atoms in a molecule. Example: $C_6H_{12}O_6$ (glucose)

• Empirical Formula: Shows the simplest whole-number ratio of atoms. Example: $CH_2O$ (for glucose)

Ionic Compounds and Properties

Structure of Ionic Compounds

Ionic compounds consist of a lattice of positive and negative ions arranged in a crystal structure.

• Formula Unit: The simplest ratio of ions in an ionic compound.

• Example: NaCl consists of Na+ and Cl- ions.

Properties of Ionic Compounds

• High melting and boiling points

• Conduct electricity when dissolved in water (electrolytes)

• Often soluble in water due to water's partial charges

Naming and Writing Formulas for Compounds

Binary Ionic Compounds

• Type I: Metals that form only one type of cation (Groups 1A, 2A, 3A)

• Type II: Metals that form more than one type of cation (transition metals)

Naming Rules

• Type I: Name the cation, then the anion with -ide suffix. Example: NaCl = sodium chloride

• Type II: Indicate the charge of the cation with Roman numerals. Example: FeCl2 = iron(II) chloride

• Polyatomic ions: Use parentheses if more than one is present. Example: Ca(NO3)2

Naming Covalent Compounds

• Use prefixes to indicate the number of each atom:

  Prefix	Number
  mono-	1
  di-	2
  tri-	3
  tetra-	4
  penta-	5
  hexa-	6
  hepta-	7
  octa-	8
  nona-	9
  deca-	10

• Drop the vowel of the prefix if needed for pronunciation.

• Example: CO2 = carbon dioxide

Acids and Bases

Naming Acids

• If the anion ends in -ide: hydro- prefix and -ic suffix. Example: HCl = hydrochloric acid

• If the anion ends in -ate: -ic acid. Example: HNO3 = nitric acid

• If the anion ends in -ite: -ous acid. Example: HNO2 = nitrous acid

Covalent Bonding and Electronegativity

Bond Polarity

• Nonpolar Covalent Bond: Electrons are shared equally.

• Polar Covalent Bond: Electrons are shared unequally, creating partial charges.

• Electronegativity: The ability of an atom to attract electrons in a bond.

  • Increases across a period, decreases down a group.

  • Fluorine is the most electronegative element.

Lewis Structures and Formal Charge

Drawing Lewis Structures

• Count total valence electrons.

• Arrange atoms and distribute electrons to satisfy the octet rule.

• Use single, double, or triple bonds as needed.

Formal Charge

• Formal charge = (valence electrons) - (nonbonding electrons) - 1/2(bonding electrons)

• Structures with formal charges closest to zero are preferred.

Resonance Structures

• Some molecules have multiple valid Lewis structures; the true structure is a hybrid.

• Example: Ozone (O3)

Molecular Geometry and VSEPR Theory

Bond Angles and Shapes

• Bond Angle: The angle between two adjacent bonds.

• Electron domains (EDs) determine molecular shape.

• Common shapes and angles:

  Shape	Bond Angle
  Linear	180°
  Trigonal planar	120°
  Tetrahedral	109.5°
  Trigonal pyramidal	107°
  Bent	104.5°

VSEPR Theory

• Valence Shell Electron Pair Repulsion (VSEPR) Theory predicts molecular shapes based on repulsion between electron domains.

• Example: H2O is bent due to two lone pairs on oxygen.

Polarity of Molecules

• Determined by the symmetry of the molecule and the distribution of polar bonds.

• Example: CO2 is linear and nonpolar; H2O is bent and polar.

Summary Table: Common Molecular Shapes

Shape	Electron Domains	Bond Angle	Example
Linear	2	180°	CO2
Trigonal planar	3	120°	BF3
Tetrahedral	4	109.5°	CH4
Trigonal pyramidal	4 (1 lone pair)	107°	NH3
Bent	4 (2 lone pairs)	104.5°	H2O

Additional info:

• These notes cover key concepts from General Chemistry chapters on bonding, molecular structure, and shapes, including naming conventions, Lewis structures, formal charge, resonance, and VSEPR theory.

• Students should be able to apply these principles to predict molecular geometry, polarity, and chemical properties.