Chapter 6: Ionic and Molecular Compounds – Study Guide

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Chapter 6: Ionic and Molecular Compounds

6.1 Ions: Transfer of Electrons

This section introduces the formation of ions through the transfer of electrons, the octet rule, and the distinction between ionic and covalent bonds. Atoms seek stable electron configurations, often achieved by gaining or losing electrons.

Ionic Bonds: Formed when electrons are transferred from metals to nonmetals, resulting in positive (cations) and negative (anions) ions.
Covalent Bonds: Formed when electrons are shared between nonmetals, creating molecules.
Octet Rule: Atoms tend to gain, lose, or share electrons to achieve eight electrons in their valence shell.
Cations: Metals lose electrons (e.g., Na → Na+, Mg → Mg2+).
Anions: Nonmetals gain electrons (e.g., Cl → Cl-).
Charge Determination: The charge of an ion is determined by the difference between the number of protons and electrons.
Periodic Table Trends: The group number helps predict the charge of ions formed by elements.

Comparison of ionic and covalent bond formation Formation of sodium ion (Na+) Formation of magnesium ion (Mg2+) Formation of chloride ion (Cl-) Periodic table of common ion charges

Example: Sodium (Na) loses one electron to become Na+, while chlorine (Cl) gains one electron to become Cl-.

6.2 Ionic Compounds

Ionic compounds are formed from the electrostatic attraction between cations and anions. Their chemical formulas reflect the lowest whole-number ratio of ions needed to balance charges.

Common Examples: NaCl (table salt), NaHCO3 (baking soda), Mg(OH)2 (Milk of Magnesia), CaCO3 (calcium carbonate).
Properties: High melting points due to strong ionic attractions.
Formula Writing: The total positive charge must equal the total negative charge.
Subscripts: Indicate the number of each ion required for charge neutrality.

Formation of NaCl, sodium chloride Formation of MgCl2, magnesium chloride Formation of Na2S, sodium sulfide

Example: In MgCl2, two Cl- ions are needed to balance the +2 charge of Mg2+.

6.3 Naming and Writing Ionic Formulas

Ionic compounds are named using systematic rules. The metal ion is named first, followed by the nonmetal ion with the suffix "-ide." Transition metals require Roman numerals to indicate their charge.

Binary Ionic Compounds: Name = Metal + Nonmetal (with "-ide").
Transition Metals: Use Roman numerals to indicate charge (e.g., iron(II), iron(III)).
Charge Balance: Subscripts are determined by the need to balance charges.
Formula Writing: Write element symbols and add subscripts to balance charge.

Table of common ionic compounds and their names Table of transition metal ions and their names Charge calculation for CuCl2 Table of systematic names for ionic compounds List of ionic compound names

Example: FeCl2 is named iron(II) chloride, while Fe2O3 is iron(III) oxide.

6.4 Polyatomic Ions

Polyatomic ions are groups of covalently bonded atoms with an overall charge. They are commonly found in ionic compounds and follow specific naming conventions.

Common Polyatomic Ions: Most end in "-ate" or "-ite" (e.g., phosphate, phosphite).
Charge and Formula: The charge and formula must be memorized for common polyatomic ions.
Examples: CO32- (carbonate), HCO3- (hydrogen carbonate), ClO4- (perchlorate).
Usage: Polyatomic ions are used in both naming and writing formulas for compounds.

Table of phosphate and phosphite ions Table of carbonate and hydrogen carbonate ions Table of chlorine-based polyatomic ions Table of polyatomic ions in medical use

Example: The formula for hydrogen carbonate (bicarbonate) is HCO3-.

6.5 Molecular Compounds: Sharing Electrons

Molecular compounds are formed by the sharing of electrons between nonmetals, resulting in covalent bonds. Their naming uses prefixes to indicate the number of atoms.

Covalent Bonds: Atoms share electrons to form molecules (e.g., H2O, CO2).
Naming: The first element is named by its element name; the second uses the root plus "-ide." Prefixes indicate the number of atoms (mono-, di-, tri-, etc.).
Formula Writing: Prefixes are used to write formulas from names.
Examples: NCl3 (nitrogen trichloride), SiBr4 (silicon tetrabromide).

Table of numerical prefixes for molecular compounds Table of molecular compounds and their commercial uses Flowchart for naming chemical compounds

Example: Carbon dioxide (CO2) is named using the prefix "di-" for two oxygen atoms.

Practice and Application

Practice problems and tables reinforce the concepts of naming and writing formulas for ionic and molecular compounds, as well as identifying polyatomic ions and their uses.

Practice Naming: Magnesium chloride, sodium sulfide, copper(I) oxide, zinc phosphide, gold(III) nitride, cobalt(III) fluoride.
Polyatomic Ion Formulas: Hydrogen carbonate (HCO3-), ammonium (NH4+), phosphite (PO33-), chlorate (ClO3-).
Polyatomic Ion Names: SO42- (sulfate), CO32- (carbonate), HSO3- (hydrogen sulfite), NO3- (nitrate).
Commercial Uses: AlPO4 (antacid), Zn3(PO4)2 (dental cement), N2O (inhaled anesthetic), Mg(OH)2 (laxative).
Formula Writing: Tin(II) carbonate (SnCO3), lithium phosphide (Li3P), silicon tetrachloride (SiCl4), manganese(III) oxide (Mn2O3), tetraphosphorus triselenide (P4Se3), calcium bromide (CaBr2).

Practice: polyatomic ion formulas Practice: polyatomic ion names Practice: commercial uses of compounds Practice: formula writing for compounds

Key Equations and Concepts

Ionic Charge Calculation:
Charge Balance in Ionic Compounds:

Additional info: The notes include tables and flowcharts for systematic naming, charge determination, and commercial/medical uses of compounds, providing a comprehensive overview for exam preparation.