Chapter2 - Molecules

Chapter 2: Atoms, Molecules, and Ions

Page 1: Fundamental Chemical Laws

  • Conservation of Mass

    • Total mass of reactants equals total mass of products.

  • Definite Proportion

    • A given compound always has the same proportion of elements by mass.

  • Multiple Proportions

    • When two elements form a series of compounds, the ratios of the masses of the second element that combine with 1 g of the first can be reduced to small whole numbers.

Page 2: Dalton’s Atomic Theory

  • Simplified Theory

    1. Elements consist of atoms.

    2. Atoms of the same element are identical; different elements have different atoms.

    3. Compounds form with consistent ratios of atoms.

    4. Chemical reactions involve rearrangement of atoms, not changes to the atoms themselves.

Page 3: Fundamental and Dalton’s Laws

  • Example of Sulfur and Oxygen

    • Sulfur can react with oxygen to form sulfur dioxide (SO2) and sulfur trioxide (SO3).

    • In SO2: 32.06 g of sulfur and 32.00 g of oxygen.

    • In SO3: 32.06 g of sulfur and 48.00 g of oxygen.

    • Ratio of weights of oxygen to sulfur: 48.00 g O : 32.06 g S reduces to 3:2.

  • Law of Multiple Proportions

    • Ratios are whole numbers, illustrating the law.

Page 4: Chemical Statements and Dalton's Theory

  • Chemical Reactions

    • Example: H2 + Cl2 → 2HCl demonstrates atom rearrangement.

  • Atoms as Basic Units

    • 3.01 × 10^23 atoms in 20.04 g of calcium.

  • Element Identity

    • Lead does not change to chromium in reactions, supporting atom identity.

Page 5: Atomic Structure

  • Structure Overview

    • Dense nucleus contains protons (positive) and neutrons (neutral).

    • Electrons (negative) are in a cloud around the nucleus.

  • Proton Count

    • Number of protons equals number of electrons in a neutral atom.

    • Number of protons determines the element's identity.

  • Periodic Table

    • Elements are ordered by the number of protons; pay attention to groupings.

Page 6: Molecules and Ions

  • Molecules

    • Collections of atoms covalently bonded (sharing electrons).

  • Ions

    • Atoms or molecules that have gained or lost electrons.

    • Cation: Positively charged ion.

    • Anion: Negatively charged ion.

  • Ionic Bonds

    • Interaction between cations and anions.

  • Element Properties

    • Elements in the same group have similar properties.

    • Metals tend to form cations; nonmetals tend to form anions.

Page 7: The Periodic Table

  • Metals

    • Most elements, tend to lose electrons, malleable, ductile, good conductors.

  • Nonmetals

    • Lack metallic properties, tend to gain electrons.

  • Groups/Families

    • Columns with chemically similar elements.

  • Rows/Periods

    • Elements in rows share the same energy levels.

Page 8: Covalent Substances

  • Example of Sulfur

    • Combines with two oxygen atoms to form molecules (not compounds).

    • Sulfur (16 protons) forms SO2 and SO3.

Page 9: Common Ions

  • Common Cations and Anions

    • Lists of common ions including Type I and Type II cations and monatomic anions.

Page 10: Oxidation States

  • Oxidation States by Element Position

    • Predicting oxidation states for elements like Cs, Br, Al, N, K, and S.

Page 11: Naming Compounds

  • Naming Conventions

    • Depends on whether the compound is binary, Type I, Type II, Type III, or contains polyatomic ions.

Page 12: Naming Compounds: Type 1

  • Binary Ionic Compounds

    1. Cation named first, anion second.

    2. Monatomic cation takes the element's name.

    3. Monatomic anion takes root + -ide.

  • Examples

    • NaCl: Sodium chloride.

    • Li3N: Lithium nitride.

    • MgO: Magnesium oxide.

Page 13: Naming Compounds: Type 2

  • Binary Ionic Compounds (Transition Metals)

    1. Same rules as Type 1.

    2. Charge specified by Roman numeral for monoatomic cations.

  • Examples

    • CuCl: Copper (I) chloride.

    • HgO: Mercury (II) oxide.

    • Fe2O3: Iron (III) oxide.

Page 14: Naming Compounds: Type 3

  • Binary Nonmetal Compounds

    1. First element named first.

    2. Second element named as an anion.

    3. Prefixes denote number of atoms.

  • Examples

    • NO: Nitrogen oxide.

    • N2O: Dinitrogen oxide.

    • NO2: Nitrogen dioxide.

Page 15: Naming Compounds: Polyatomic Ions

  • Memorization

    • Polyatomic cations and anions have specific names that need to be memorized.

Page 16: Naming Compounds: Acids

  • Binary Acids

    • Anion ending in -ide: add hydro- and change -ide to -ic.

  • Oxoacids

    • Anion ending in -ate: change -ate to -ic.

    • Anion ending in -ite: change -ite to -ous.

Page 17: Practice Makes Perfect

  • Review and Exercises

    • Review all questions and complete exercises 20, 21, 24, 25, 28-36, 39-46, 53-56, 59-70, 75-92.

    • Additional exercises, ChemWork, and challenge problems are also included.