CHYS-161 Unit 05 Chemical Compounds

Unit 5 Overview

  • Topic: Chemical Compounds

    • Focus Areas:

      • Chemical Bonding and Formulas

      • Covalent Bonding and Nomenclature

      • Ionic Bonding and Nomenclature

      • Overview of Acids and Nomenclature

Learning Objectives

Molecular and Ionic Compounds

  • Define ionic and molecular (covalent) compounds.

  • Predict types of compounds formed from elements based on periodic table locations.

Concepts of Chemical Bonding

  • Bonds connect atoms within a molecule or compound.

  • Bonds determine the 3-D shape of molecules.

Types of Bonding (Intramolecular Forces)

  1. Metallic Bonds

  2. Covalent Bonds

  3. Ionic Bonds

Chemical Nomenclature

  • Types of Compounds:

    • Molecular (Covalent)

      • Binary (2 element) compounds

    • Ionic

      • Binary (2 element)

      • Compounds containing polyatomic ions

      • Acids

  • Rules for Naming Compounds:

    • Identified by formula (chemical symbols)

    • Name written in English with correct spelling.

Types of Chemical Bonds

  • Covalent Bond: Electrons are shared.

  • Ionic Bond: Electrons are transferred, forming ions.

    • Metals lose electrons to form cations.

    • Nonmetals gain electrons to form anions.

    • Electrostatic forces hold ions together.

Metallic Bonding

  • Structure:

    • Crystalline lattice of metal cations in a sea of valence electrons (single metal).

  • Definition: Names or formulas of metals.

Learning Objectives - Covalent Bonding

  • Describe the formation of covalent bonds.

  • Define electronegativity and assess polarity of covalent bonds.

  • Derive names for common inorganic compounds systematically.

Covalent Bonding Definition

  • Covalent Bond: Electrons shared between two nonmetal atoms.

    • Nonmetals share electrons to fill valence orbitals.

    • Example: Hydrogen (H) molecules (H-H = H2).

Types of Covalent Bonds

  1. Non-polar (pure) Covalent Bond

    • Electrons shared equally (e.g., diatomic molecules).

  2. Polar Covalent Bond

    • Electrons shared unequally between elements of different electronegativities (e.g., H-F).

Electronegativity

  • Key to understanding how electrons are shared.

  • Electronegativity increases across the periodic table.

Electronegativity and Bond Type

  • Pure Covalent:

    • Electronegativity difference < 0.4

  • Polar Covalent:

    • Electronegativity difference between 0.4 - 1.8

  • Ionic:

    • Electronegativity difference > 1.8

Chemical Formulas

  • Definition: Consist of chemical symbols and subscripts indicating atom counts in compounds.

  • Molecular Formula: Represents a molecule or compound.

Subscripts and Coefficients

  • Subscript: Number to the right of an element symbol indicates atom quantity.

  • Coefficient: Number in front of the chemical formula indicates molecular quantity.

Diatomic Molecules

  • Common diatomic molecules: H2, N2, O2, F2, Cl2, Br2, I2.

  • Sulfur: Most common form is S8.

Naming Covalent (Molecular) Compounds

  • Significant variation in atom ratios (e.g., NO, NO2, N2O, N2O3).

  • Naming convention:

    1. Name less electronegative element first.

    2. Use Greek prefixes for atom quantity.

Naming Covalent (Molecular) Compounds Details

  1. Name the first element (using prefixes if subscript 2+).

  2. Name the second element with suffix -ide.

    • Drop "a" or "o" from prefixes if the element begins with a vowel.

Naming Examples of Covalent Compounds

  1. Carbon dioxide: CO2

  2. Phosphorus trichloride: PCl3

  3. Diphosphorus pentoxide: P2O5

Learning Objectives - Ionic Bonding

  • Explain formation of cations, anions, and ionic compounds.

  • Predict charges of common elements and write their electron configurations.

  • Determine ionic compound formulas and names systematically.

Ionic Bonding Definition

  • Valence electrons are transferred from metals to nonmetals (or polyatomic ions).

    • Held by electrostatic forces between cations and anions.

    • Example: NaCl.

Ionic Bonding Structure

  • Stabilized by organized structures:

    • Na+ and Cl- ions arranged in a 3D lattice structure.

    • Each Na+ surrounded by 6 Cl- and vice versa.

Predicting Ion Charge

  • Main-group metals lose electrons to match preceding noble gas configuration.

    • Group 1: Forms cation with 1+ charge.

    • Group 2: Forms cation with 2+ charge.

  • Nonmetals gain electrons to match next noble gas.

    • Group 17 gains 1 electron (1– charge).

    • Group 16 gains 2 electrons (2– charge).

Predicting Ion Charge from Periodic Table

Exhibit Charge Predictions

  • Group 1: H+, Li+, Na+, K+

  • Group 2: Be2+, Mg2+, Ca2+, Ba2+

  • Group 17: F–, Cl–, Br–

  • Group 16: O2–, S2–

Polyatomic Ions

  • Monatomic ions: Cl–, Na+, Ca2+.

  • Polyatomic ions (charged molecules): NO3–, SO42–, NH4+.

Ion Charges to Learn (Chem21)

  • Predict from position on Periodic Table.

  • Memorize charges of specific ions.

  • Other charges can be predicted from formulas or established resources.

Naming Oxyanions

  • Two oxyanions from a nonmetal:

    • -ate for larger, -ite for smaller.

  • More than two oxyanions: use per- (largest) or hypo- (smallest).

Formulas of Ionic Compounds

  • Ionic compounds must be electrically neutral.

  • Positive and negative charges must balance in the formulas.

    • Example: Na gives Na+, Cl accepts electron makes Cl– to form NaCl.

    • Example: Ca2+ gives two electrons, two Cl– together form CaCl2.

    • Example: Mg2+ and O2– form MgO; Al3+ and O2– form Al2O3.

Predicting Formulas of Ionic Compounds

  • Criss-Cross Method:

    • Na+ and Cl– form NaCl.

    • Mg2+ and NO3– form Mg(NO3)2.

    • K+ and PO43– form K3PO4.

Predicting Examples of Ionic Compounds

  1. Mg and Cl: MgCl2

  2. Al and S: Al2S3

  3. Pb and N: Pb3N4

Naming Ionic Compounds

  1. Cation Naming:

    • Fixed charge: Use element name.

      • E.g., Na+ as Sodium ion.

    • Variable charge: Use name followed by charge in Roman numerals (e.g., Iron(II)).

    • Polyatomic ions use polyatomic ion names (e.g., NH4+ as Ammonium).

Naming Anions

  1. Anion Naming:

    • Monoatomic ions: Use name, replace ending with -ide (Cl– to Chloride).

    • Polyatomic ions: Use name of the polyatomic ion (SO42– to Sulfate).

Naming Ionic Compounds Examples

  1. Na+ and O2-: Na2O (Sodium oxide)

  2. Zn2+ and Cl–: ZnCl2 (Zinc chloride)

  3. Ca2+ and NO3–: Ca(NO3)2 (Calcium nitrate)

  4. Cu2+ and N3–: Cu3N2 (Copper(II) nitride)

Naming Acids

  • Compounds beginning with H: Acids.

  • Increase concentration of H+ ions in water.

  • Naming depends on anion suffix:

    • -ide becomes hydro-______-ic acid.

    • -ate becomes ______-ic acid.

    • -ite becomes ______-ous acid.

Naming Acid Examples

  • HI: Hydroiodic acid (I-).

  • HNO3: Nitric acid (NO3-).

  • H2SO3: Sulfurous acid (SO32-).