CEM 141: Introduction to Chemistry and Atomic Theory

Chemistry

Study of matter and its interactions.

Scientific Model

Predicts outcomes under untested conditions.

Claim

Prediction supported by evidence.

Evidence

Data supporting a scientific claim.

Reasoning

Connection between claim and evidence.

Scientific Theory

Best explanation based on existing evidence.

Scientific Law

Describes phenomena; tells what happens.

Hypothesis

Testable prediction based on observations.

Atom

Smallest unit of an element.

Molecule

Collection of two or more atoms.

Element

Substance made of identical atoms.

Brownian Motion

Random motion of particles in fluid.

Kinetic Energy

Energy of motion in atoms.

Atomic Theory

Concept of indivisible particles called atoms.

Proton

Positive particle defining element identity.

Nanometer

Unit measuring atomic scale; 0.1 x 10^-9 m.

Indestructible

Property of atoms; cannot be created or destroyed.

Replicable Experiments

Experiments that can be repeated with same results.

Philosophical Ideas

Concepts based on reasoning, not experimental evidence.

Macroscopic Sample

Visible collection of atoms or molecules.

Energy Transfer

Movement of energy during collisions.

Denatured Protein

Altered protein structure affecting size comparison.

Dalton's Atomic Theory

Early theory stating atoms are indivisible.

Subatomic Particles

Particles smaller than atoms: protons, neutrons, electrons.

Isotopes

Atoms of the same element with different neutron counts.

Chemical Reactions

Rearrangements of atoms; matter is conserved.

Electron Discovery

First subatomic particle discovered, negatively charged.

Thomson's Experiment

Showed all atoms contain electrons via cathode ray.

Cathode Ray Tube

Device demonstrating electron behavior in low pressure.

Plum Pudding Model

Atom model with evenly distributed positive and negative charges.

Rutherford's Experiment

Demonstrated existence of a dense, positive nucleus.

Alpha Particles

Helium nucleus; used in Rutherford's scattering experiment.

Electron Cloud

Region around nucleus where electrons are likely found.

Forces in Atoms

Interactions include gravitational, electromagnetic, strong, and weak forces.

Gravitational Force

Attraction between objects with mass; increases with mass.

Electromagnetic Force

Attraction/repulsion between charged objects.

Strong Force

Short-range force holding protons and neutrons together.

Weak Force

Short-range interaction affecting elementary particles.

Nucleus

Dense center of an atom containing protons and neutrons.

Neutrons

Neutral particles residing in the nucleus, slightly heavier.

Charge Manipulation

Charged particles can be influenced by magnetic fields.

Mass Number

Total number of protons and neutrons in an atom.

Opposite Charges

Attract each other; like charges repel.

Atom Structure

Atoms consist of a nucleus and electron cloud.

Newton's law of universal gravitation

Describes force between two masses inversely proportional to distance squared.

Inverse-square law

Force decreases with the square of distance increase.

Gravitational forces

Attractive forces between two masses mediated by fields.

Gravitational fields

Regions around masses where gravitational forces act.

Electromagnetic force

Stronger than gravity; can be attractive or repulsive.

Electrostatic force

Forces between charged particles, governed by Coulomb's law.

Coulomb's law

Electrostatic force proportional to product of charges.

SI unit of energy

Joule, equivalent to kg m² s⁻².

First law of thermodynamics

Energy cannot be created or destroyed, only transformed.

Kinetic energy

Energy associated with an object's motion, KE = ½mv².

Potential energy

Energy related to an object's position in a field.

Energy conservation

Energy can be transferred or transformed, not lost.

System

Part of the universe under study.

Surroundings

Everything outside the system in thermal contact.

Energy types

Includes chemical, nuclear, heat, kinetic, electrical, thermal.

Kinetic and potential energy

Two main groups of energy related at molecular level.

Gravitational force

Attractive force acting between masses.

Electromagnetic force

Force acting at a distance through electric and magnetic fields.

Change in energy

Caused by changes in force acting on a system.

Field

Region where forces act on objects with mass or charge.

Energy transformation

Change of energy from one form to another.

Attractive force

Force that pulls objects towards each other.

Atomic interactions

Forces between charged particles in atoms.

Coulomb's law

Describes electrostatic interaction between charged particles.

Molecules

Formed when atoms stick together.

Freezing

Transition from liquid to solid state.

Condensation

Transition from gas to liquid state.

Helium

Noble gas with low reactivity and specific melting/boiling points.

Melting point of Helium

0.95 K (-272.2 °C) at which it becomes solid.

Boiling point of Helium

4.5 K (-268.5 °C) at which it becomes gas.

Instantaneous dipole

Temporary charge separation in atoms due to electron cloud distortion.

London dispersion force (LDF)

Weak attraction between neutral atoms due to dipoles.

Electrostatic force

Force between charged particles; increases as distance decreases.

Potential energy (PE)

Energy stored due to position; decreases as atoms approach.

Kinetic energy (KE)

Energy of motion; inversely related to potential energy.

Electrostatic attraction

Force pulling charged particles together.

Electrostatic repulsion

Force pushing charged particles apart.

Energy conservation

Total energy remains constant in atomic interactions.

Thermal energy

Energy related to temperature; affects atomic motion.

Temperature

Measure of thermal energy in a system.

Collision

Event where kinetic energy transfers between atoms.

Potential minimum

Lowest potential energy state for interacting atoms.

Energy input

Adding energy to break atomic interactions.

Energy output

Removing energy to maintain atomic interactions.

Thermal energy

Sum of kinetic energies of all atoms.

Temperature (T)

Directly related to average kinetic energy.

Energy transfer in heating

Occurs via collisions with container walls.

Energy absorption

Necessary for breaking attractive interactions between atoms.

Helium (He) electrons

He has 2 electrons.

Xenon (Xe) electrons

Xe has 54 electrons.

Electron cloud distortion

Larger atoms have floppier electron clouds.

London dispersion force (LDF)

Intermolecular force increasing with atom size.

Factors increasing LDF strength

Size of atom and surface area.

Intermolecular forces

Range of interactions between particles.

Melting point of He

He has a melting point of 1K.

Melting point of Xe

Xe has a melting point of 161K.