notes-04_Lecture-2025spring
Chapter 4: Basic Chemical Bonding
Elements and Compounds
Elements combine to form numerous compounds similar to how letters form words.
Key Point: The properties of compounds differ from those of the constituent elements.
Chemical Bonds
Compounds are made up of atoms connected through chemical bonds.
Definition: Chemical bonds represent the attraction forces between atoms, originating from the interactions between protons and electrons.
Why Do Atoms Bond?
Atoms bond to lower their energy state, forming stable interactions:
Nucleus–to–nucleus repulsion
Electron–to–electron repulsion
Nucleus–to–electron attraction
A chemical bond forms when the potential energy of bonded atoms is lower than that of separate atoms.
Energy decreases when bonds form, foundational concept in quantum mechanics.
Bond Types
Ionic Bonds: Result from the transfer of electrons, usually between metals and nonmetals.
Covalent Bonds: Formed when two atoms share electrons, typically between nonmetals.
Page 2: Representing Compounds with Chemical Formulas
Chemical Formulas
Chemical formulas convey information about the elements in a compound using symbols.
Not all formulas accurately represent the structure of the compound.
Types of Formula
Empirical Formula
Represents the relative number of each atom in a compound, does not provide info on the structure or order.
Example: Calcium Fluoride (CaF2).
Molecular Formula
Gives the actual number of atoms in a compound.
Example: Oxalic Acid (C2H2O4).
Structural Formula
Illustrates how atoms are connected using lines for bonds.
Single bond: 2 electrons, double bond: 4 electrons, triple bond: 6 electrons.
Molecular Models
Ball-and-stick models: Visual representation of atoms and their bonds.
Space-filling models: Show electron clouds of atoms.
Classifying Elements & Compounds
Atomic Elements: Single atoms.
Molecular Elements: Multi-atom molecules (e.g., diatomics)
Molecular Compounds: Made of nonmetals.
Ionic Compounds: Composed of cations and anions.
Page 3: Molecular View of Elements and Compounds
Elements
Atomic Elements: Most consist of single atoms not chemically bound together.
Molecular Elements: Made of multi-atom molecules bound by covalent bonds (e.g., diatomics: H2, O2).
Compounds
Comprised of ions in a 3D arrangement (ionic compounds) or molecules with covalent bonds (molecular compounds).
Differences Between Ionic and Molecular Compounds
Example of propane as a molecular compound versus sodium chloride as an ionic compound.
Classification Exercise
Classify elements and compounds as atomic, molecular, ionic, or molecular compounds.
Examples: Aluminum (Al) = Atomic Element, Aluminum Chloride (AlCl3) = Ionic Compound.
Page 4: Ionic Compounds
Formation of Ionic Compounds
Ionic compounds consist of metals and nonmetals exhibiting ionic bonds; metals form cations and nonmetals form anions.
Compounds must overall balance charge.
Examples of Ionic Compounds
Sodium and Sulfur: Na2S is needed to balance charges.
Aluminum and Oxide: Al2O3 results from balancing Al3+ and O2− ions.
Naming Ionic Compounds
Involves determining cation and anion names, includes special rules for metals with invariant or variable charges.
Page 5: Naming Ionic Compounds
Rules for Naming
Systematic naming involves naming the cation first followed by the anion, noting charges for variable cations.
Binary Ionic Compounds: Metal cation + nonmetal anion.
Cation is named first; anion's name modified to -ide.
Metals with Variable Charges
Named using Roman numerals to indicate charge based on the oxidation state.
Page 6: Polyatomic Ions
Characteristics of Polyatomic Ions
Composed of multiple atoms that act as one ion.
Identified through their names and charges without changing them.
Naming Ionic Compounds with Polyatomic Ions
Example: Na2SO4 involves identifying sodium (Na+) and sulfate (SO4^2−).
Page 7: Writing Names of Binary Molecular Compounds
Rules for Molecular Compounds
Name the first nonmetal using the full element name.
Name the second nonmetal with an -ide suffix and use prefixes to indicate quantities.
Page 8: Acids
General Features of Acids
Produce H+ in solution and are characterized by sharp taste.
Binary Acids: Contain H+ and a nonmetal anion.
Oxyacids: Contain H+ and polyatomic oxyanions.
Naming Acids
Binary Acids: Prefix “hydro-” + anion name with -ic + “acid”.
Oxyacids: Names change based on the ending of the polyatomic ion (-ate to -ic, -ite to -ous).
Page 9: Organic Compounds
Alkanes
Only consist of carbon (C) and hydrogen (H).
Formula: CnH(2n+2).
Naming follows the format of prefix + -ane.
Bonding Theories
Fundamental to understanding chemical bonding, determining stability, shapes, and properties of compounds.
Page 10: Lewis Bonding Theory
Valence Electrons
Key in chemical bonding, primarily concerned with the transfer or sharing of electrons.
Drawing Lewis Structures
Represent valence electrons and predict molecular properties like stability and shape.
Page 11: Energetics of Ionic Bond Formation
Formation Processes
Involve ionization energy and electron affinity; generally an exothermic process.
Crystal Lattice: Arrangement of ions providing extra stability and energy release upon formation.
Page 12: Trends in Lattice Energy
Factors Influencing Lattice Energy
Ion size and charge play crucial roles in the strength of ionic bonds; larger charge indicates stronger attraction and lattice energy.
Page 13-20: Covalent Bonding
Characteristics of Covalent Bonds
Form through sharing of electrons and demonstrate directional properties, resulting in distinct molecular shapes.
Bond Types and Stability
Different bonds (single, double, triple) have varying strengths and lengths, with trends observed across the periodic table and between similar atoms.
Molecular compounds typically exhibit lower melting points compared to ionic compounds.
Resonance and Formal Charge
Understanding resonance in structures allows predictions of molecular behavior and stability, guiding the conception of Lewis structures and their modifications (e.g., radicals, incomplete octets).
Bond Energies and Lengths
Bond energies correlate with bond types and strength. Bond lengths decrease with greater shared electrons.
Properties of Metals
Metal bonding characterized by electron delocalization provides conductive, malleable properties.
Summary of Key Concepts
Chemical Bonds: Atoms bond via ionic or covalent means.
Naming Conventions: Systematic approaches to naming ionic and molecular compounds.
Bonding Theories: Lewis theory and resonance concepts are crucial for predicting molecular behavior and stability.