lewis structures

Introduction

  • Question was raised about the testing center schedule and operations.
  • Instructor emphasized the importance of students being prepared for the upcoming exams, particularly in the first week.

Testing Center Overview

  • Current Testing Center Availability:
    • Week zero testing schedule is displayed.
    • Students must check the schedule for available times.

Bubble Sheet Requirement

  • Students need to print and bring their Gradescope bubble sheets when attending the testing center.
    • The same bubble sheet is used for all exams.
    • If taking multiple exams, ensure to print one bubble sheet for each exam attempted.
    • Limited copies available from the instructor; students should print their own to avoid shortage.

Exams Availability

  • Only Unit 1 and Unit 2 exams are available this week (Week Zero).
  • Students may attempt the units multiple times:
    • One version of the exam is available on Monday and Tuesday.
    • Another version is available on Wednesday and Thursday.

Unit 3 Exam Information

  • The Unit 3 exam is to be taken during discussion sessions.
  • Students are reminded to bring their Gradescope bubble sheet, as the TA will provide an exam booklet.
  • Submission requirements:
    • Turn in the exam booklet, completed bubble sheet, and scratch paper before leaving.

Exam Format and Policies

  • Exams will be in paper format from this point onwards.
  • Strict adherence to policy:
    • No writing in the exam booklet itself is allowed, in an effort to preserve exam materials.
    • Ensure all materials are collected at the end of the exam.

Upcoming Midterm

  • The first midterm exam will occur next week, covering Units 1 through 3.
  • Students are reminded to bring their Gradescope bubble sheet for the midterm.
  • Structure of the midterm exam:
    • 20 questions total breakdown is as follows:
    • 10 questions from Unit 3
    • 6 questions from Unit 2
    • 4 questions from Unit 1
  • The total exam duration is 50 minutes.
  • Additional support will be provided for Unit 3 before the midterm.

Exam Logistics

  • Testing center will focus on Unit 4 retakes during the midterm week.
  • Coverage of Units 1 through 3 will provide foundation for forthcoming units.

Preparation and Retakes

  • Students encouraged to take advantage of retakes for mastery units 1 and 2 this week to solidify understanding.
  • The instructor will provide a summary announcement recapping all points discussed in the lecture regarding exams and preparation.

Start of Week 5 Content

Electron Configuration Activity

  • Activity involves electron configuration of elements as it relates to examinations.
  • Electronic configuration will establish foundation for further studies in Unit 4.

Example: Calcium

  • For calcium (Ca), with atomic number 20:
    • Ground state electron configuration is (1s^2 2s^2 2p^6 3s^2 3p^6 4s^2).
    • This indicates it has 2 valence electrons represented in the 4s orbital.

Br- Ion Example

  • For bromide ion (Br-), atomic number 35:
    • Addition of an electron (due to the -1 charge).
    • Ground state electron configuration is (1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6), matching the noble gas configuration of krypton.

Copper Example

  • Ground state electron configuration of copper (Cu), atomic number 29:
    • Normal expectation would be (1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{9}), however due to energetics it is:
    • (1s^2 2s^2 2p^6 3s^2 3p^6 4s^{1} 3d^{10}) where the stability of a full d orbital is preferred.

Trends in Ionic Size

General Rules

  • The size of ions can be influenced by:
    • Principal quantum number (n) - larger n indicates a larger size.
    • Charge - more negative ions are larger due to electron-electron repulsion.

Comparison of Ions

  1. Decreasing Ion Size:
    • Order: Strontium (Sr) > Calcium (Ca) > Magnesium (Mg) based on principal quantum numbers (n=5, 4, and 3 respectively).
  2. Electrons and Nucleus:
    • Ions with the same electron configuration but varying nuclear charge will have different sizes depending on proton count.
    • Example: S2- > Cl- > K+ due to nuclear charge:
      • S (16 protons) is larger than Cl (17 protons) and K (19 protons) in their corresponding ion forms.

Summary and Transition to New Material

Overview of Chemical Bonding

  • Introduction of chemical bonds to explain how atoms connect to create molecules.
  • Types of Chemical Bonds:
    • Ionic Bonds:
    • Electrostatic attraction between cations and anions.
    • Example: Sodium Chloride (NaCl).
    • Covalent Bonds:
    • Sharing of electrons between atoms (common in biomolecules and organic compounds).
    • Example: Proteins making up viral capsids.
    • Metallic Bonds:
    • Electrons are delocalized within a metal structured allowing for conductivity.

Future Topics

  • In-depth exploration of Lewis Structures, BSEPR theory for molecular shape, and polarity.
  • Transition into Unit 4 will utilize concepts from quantum mechanics in practical chemical bonding applications, minimizing complex mathematical derivations.