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: S^2- > 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.