Office hours today: 1:00–2:00 PM in this class room; bring your calculator.
Alex homework due Sunday for modules 2A and 2B.
Mini exam scheduled for Friday, Sept 12, in this room, at 11:30–12:20 (exam duration is 25 minutes).
For accommodations, students approved for extended time must schedule the exam with the testing center by this week (tonight). The instructor will not administer accommodated exams here.
The practice mini exam is not graded; it is for preparation and will be posted in the Canvas mini exam folder.
Exam format: 10 questions, 25 minutes; time is short to allow for seating and setup.
If you have questions about the mini exam, raise your hand during class or ask on Monday for clarification; more details will be provided then.
All topics for the mini exam come from today’s class onward; content will be posted in Canvas under the Mini exam preparation folder (practice worksheets, videos, study guide).
The instructor plans to upload additional practice worksheets and a detailed study guide with examples and slide pictures to help you study specific topics.
Review focus: material from Unit 1 up to today; topics include SigVic, unit conversions, accuracy vs precision, matter and its classifications, physical vs chemical changes, atoms/ions/isotopes, cations, anions, polyatomic ions, memorization list of polyatomic ions (to be provided in study guide), average atomic mass and percent abundance, ionic vs covalent compounds, writing formulas, predicting ion charges, naming ionic and covalent compounds, and naming conventions for covalent compounds.
The mini exam content will be posted in Canvas; you do not need to complete the optional extra worksheets unless you want extra practice.
Key Concepts and Topics Covered (Review)
SigVic concepts (as referenced in lecture):
Unit conversions
Accuracy vs precision
Substances: pure substances vs mixtures; physical changes vs chemical changes
Atoms, ions, and isotopes; definitions of isotopes; ion types (cation, anion) and polyatomic ions
Memorized polyatomic ions to be provided in the study guide
Average atomic mass and percent abundance
Ionic vs covalent compounds; writing ionic formulas; predicting ion charges; naming ionic and covalent compounds
Ionic vs Covalent compounds: quick distinctions
Ionic compounds: metal + nonmetal or polyatomic ions; may form lattice structures
Covalent (molecular) compounds: one or more nonmetals; exist as discrete molecules; typically do not form lattice structures
Writing formulas for ionic compounds (examples)
Example: Cr2+ with iodide (I−) → formula: ext{CrI}_2
The cation is Cr^{2+} (transition metal → charge shown in name) and the anion is I^−; charges balance via exchange to give CrI_2
Example: Ammonium phosphate with ammonium NH4^+ and phosphate PO4^{3−}
To balance -3, two ammonium ions would give +2, not enough; but the transcript example shows balancing as ammonium phosphate with charge balance, explicitly: ext{(NH}4)3 ext{PO}_4
Note: Phosphate carries −3, ammonium carries +1; balance by using 3 NH4^+ ions with one PO4^{3−} ion
NaCl, CaCl_2 as simple ionic compounds; breakdown into ions shows the charges and counts
NaCl: 1 Na^+ and 1 Cl^−
CaCl_2: Ca^{2+} and 2 Cl^−
Polyatomic ion naming and usage
Ammonium phosphate example shows the use of polyatomic ions in forming ionic compounds: ext{(NH}4)3 ext{PO}_4
For ammonium sulfate (polyatomic ion sulfate SO4^{2−}): ext{(NH}4)2 ext{SO}4
Transition metals in ionic compounds
When a transition metal is involved, include its charge in the name: e.g., iron(III) nitrate, nickel(II) chloride, chromium(III) oxide
Example: NiCl_2 is nickel(II) chloride because nickel is in the +2 oxidation state in that compound
Example: Fe(NO3)3 is iron(III) nitrate; iron forms Fe^{3+} in this compound
Naming covalent (molecular) compounds with prefixes
Use prefixes: mono-, di-, tri-, tetra-, penta-, hexa-, etc.
Do not use mono- for the first element; the second element ends with -ide and all elements are nonmetals
Examples from lecture:
CO_2 → carbon dioxide
N2O4 → dinitrogen tetroxide
S2Cl2 → disulfur dichloride
Cl2O7 → dichlorine heptoxide
The seven diatomic elements (as presented): H2, N2, O2, F2, Cl2, Br2, I_2 (note: standard list excludes iron; the transcript lists