Chapter 1 & 2 Lecture Notes: Scientific Explanations and Models of Matter
Course Logistics and Administrative Announcements
Homework Policy and Weekly Schedule:
Beginning next week, a strict schedule will be enforced.
Homework assignments open immediately following lecture.
Homework is due at prior to the start of the next lecture.
Due to ongoing course adds/drops during the first week, Homework 1 (the CATLIS survey) and Homework 2 (the first bisocratic activity) remain open for full credit even if not completed prior to class.
D2L Course Site:
Students are required to check the D2L course site regularly for essential course resources.
Campus Building Access and Friday Football Game Protocol:
On Fridays with home football games (including the season opener), campus buildings will be locked by campus security starting at for safety.
Students must carry their physical MSU ID card at all times to gain building access for afternoon classes or Friday lectures.
Recitation Operations:
Recitations officially begin next week.
Monday Recitations: Students enrolled in Monday sections will receive an email containing instructions for completing an asynchronous recitation activity.
Tuesday–Friday Recitations: Students in these sections must attend their scheduled recitation meetings in person.
Review of Experimental Design: Coffee and Milk Activity
Objective:
Critically evaluate student-submitted experimental procedures to ensure sufficient detail, clarity, and reproducibility so that independent researchers can perform the experiment and obtain identical results.
Student Sample Procedure Evaluation:
Materials List: Two cups of brewed coffee, one glass of cold milk, one thermometer, and one spoon/scoop.
Procedural Steps:
Prepare two cups of coffee from the exact same brew.
Obtain cold milk of choice.
Using a thermometer, measure the initial temperature of the first coffee cup to establish a control; record the value on paper.
Pour milk into the second coffee cup.
Stir the mixture gently with a spoon.
Measure the temperature of the resulting mixture; record the value.
Compare and analyze the initial control temperature against the mixture temperature.
Necessary Improvements for Replicability:
Record the starting temperature of both the brewed coffee and the cold milk prior to mixing.
Measure and specify exact quantitative volumes (e.g., volume of coffee, volume of added milk in or tablespoons).
Record detailed qualitative observations (e.g., alterations in taste, color, or opacity).
Incorporate systematic multi-step additions (e.g., adding milk in multiple sequential increments rather than a single pour) to collect multiple data points and reveal mathematical trends.
Molecular Representations and Collision Mechanisms
Visualizing Thermal Phenomena:
Macroscopic observations (coffee cooling down) must be represented at the sub-microscopic/molecular level to show the underlying physical mechanism.
Critique of Molecular Drawings:
Common Deficiencies: Unlabeled components, lack of distinct symbols or color coding to differentiate distinct particle species.
Best Practices: Use visually distinct representation symbols (e.g., solid circles versus open circles, distinct shape keys) to differentiate coffee molecules from milk molecules and label every component explicitly.
Mechanism of Energy Transfer:
Coffee cooling is governed by sub-microscopic molecular collisions.
Energy transfers directly upon collision from high-energy coffee molecules to lower-energy milk molecules.
Particle drawings must display physical collisions between coffee and milk molecules to visually represent the transfer mechanism of thermal energy.
The Claim, Evidence, and Reasoning (CER) Framework
Scientific Explanations:
Any robust scientific explanation requires three fundamental components: a Claim, Evidence, and Reasoning.
Claim:
Definition: The target statement, answer, or conclusion that addresses the original question or phenomenon.
Example: Adding cold milk to hot coffee causes the hot coffee to cool down.
Evidence:
Definition: Scientific data, observations, empirical measurements, or established scientific principles that support the validity of the claim.
Examples across phenomena:
Atomic Existence: High-resolution microscopic techniques, specifically Atomic Force Microscopy (AFM) and Scanning Tunneling Microscopy (STM), which generate computer renderings visualizing individual atoms. (Note: The Rutherford Gold Foil Experiment provided evidence specifically for the atomic nucleus, rather than atomic existence itself).
Gravitational Attraction: Universal empirical observation that dropped objects invariably accelerate toward the Earth's center (always moving downward, never upward).
Universal Ancestry: The universality of the genetic code across all known living organisms.
Coffee Cooling: Quantitative initial and final temperature readings showing a numerical temperature decrease post-mixing.
Reasoning:
Definition: The logical bridge connecting the evidence to the claim. It explicitly articulates the underlying physical cause or atomic/molecular mechanism explaining how and why the observed phenomenon occurs.
Function: Explains the physical or chemical causality behind the measured evidence.
Scientific Models and Predictive Power
Definition and Scope of Models:
A scientific model is an explanatory tool—visual, physical, conceptual, graphical, or mathematical—used to clarify phenomena, construct testable explanations, and make quantitative predictions.
Types of Models: Particle drawings, mathematical equations, graphs, diagrams, physical scale models, and mental constructs.
Graphical Models and Predictive Utility:
Example: Plotting Temperature () on the y-axis against the Volume of Milk added (in tablespoons) on the x-axis.
Construction: Plot baseline temperature at \,tablespoons, followed by discrete measurements after each incremental addition (, , , and \,tablespoons).
Predictive Power: Interpolating data points along the plotted curve allows one to accurately predict the resulting temperature for unmeasured volumes (e.g., \,tablespoons) without running an additional physical experiment.
Historical Models of the Atom
Evolution of Atomic Theories:
Scientific models evolve over time as new empirical evidence emerges. Different atomic models are selected based on their specific utility for explaining particular phenomena:
Dalton's Model: Solid, indivisible sphere.
Thomson's Model: Plum pudding model featuring embedded charges.
Rutherford's Model: Nuclear atom with centralized positive charge.
Bohr's Model: Planetary orbits with quantized energy levels.
Schrödinger's Model: Quantum mechanical model featuring electron probability clouds/orbitals.
Kinetic Energy, Temperature, and Thermal Transfer
Thermodynamic Definitions:
Temperature: A direct measure of the average kinetic energy () of the constituent particles within a system.
Kinetic Energy and Velocity: The kinetic energy of a moving particle is directly proportional to its mass and the square of its velocity:
Molecular Mechanism of Heat Exchange:
High temperature implies a high average kinetic energy, meaning particles move at higher average velocities.
Low temperature implies a low average kinetic energy, meaning particles move at lower average velocities.
Hot coffee molecules possess higher average kinetic energy and move faster than cold milk molecules.
When cold milk is mixed into hot coffee, fast-moving coffee molecules collide with slower-moving milk molecules.
Thermal energy transfers unidirectionally from hot molecules to cold molecules during kinetic collisions.
Upon collision, high-velocity coffee molecules lose kinetic energy (slowing down, causing coffee temperature to drop), while low-velocity milk molecules gain kinetic energy (speeding up, causing milk temperature to rise) until thermal equilibrium is established.
Scientific Theories versus Scientific Laws
Scientific Theory:
Definition: A comprehensive, deeply tested, dynamic explanation of observed natural phenomena based on extensive experimental data and observations.
Characteristics: Explains how and why phenomena happen; makes testable predictions; is falsifiable (capable of being proven false if contradicting empirical evidence arises); subject to revision as novel evidence is discovered.
Example: The Big Bang Theory, Theory of Evolution.
Scientific Law:
Definition: A concise verbal or mathematical statement that describes an observed pattern or universal regularity in nature under specific conditions.
Characteristics: States what happens without offering an explanation of the underlying cause or mechanism.
Example: Universal Law of Gravitation (states that the gravitational force of attraction between two masses is directly proportional to the product of their masses and inversely proportional to the square of the distance separating them):
Classroom Discussions and Knowledge Check Questions
Categorization Discussion:
Fact: An atom of hydrogen contains exactly one proton.
Scientific Law: The force of attraction between two masses is proportional to the product of their masses and inversely proportional to the square of the distance between them.
Scientific Theory: The Big Bang Theory.
Hypothesis: If reagent X is added to a reaction mixture, the overall rate of reaction will increase.
Scientific Question: What will happen to the temperature of hot coffee if cold milk is added to it?
The Atomic Hypothesis (Richard Feynman):
Core Concept: All things are made of atoms—little particles that move around in perpetual motion, attracting each other when they are a little distance apart, but repelling upon being squeezed into one another.
Composition of Matter Inquiry:
Question: Which of the following contains atoms: cells, air, gold, heat?
Analysis: Cells, air, and gold consist of matter and are composed of atoms. Heat is a form of energy transfer, not matter, and therefore does not consist of atoms.