Lecture 5 –The Atom Great Idea: “All matter is made of atoms, which have a positively-charged nucleus surrounded by negatively-charged electrons.”

Electricity and magnetism are two aspects of the same force. All magnets have both north and south poles Static electricity is manifest as a force between charged objects Electricity produces magnetic effects. Moving magnets produce electricity.

The Electrical Field The force felt by a charge located at a particular point Differs from the magnetic dipole field

Magnetic Effects from Electricity

North and South poles flip during rotary motion. The Electric Motor North and South poles flip during rotary motion.

Review – Maxwell’s Equations for Electricity & Magnetism Coulomb’s law of static electricity All magnets have both North and South poles Electricity produces magnetic fields Moving magnets produce electricity:

Maxwell’s Laws, 1855 These equations lead to prediction of waves: 1. Waves travel 186,000 miles per second 2. Light is a consequence of electricity and magnetism switching back and forth

Review – Maxwell’s Equations for Electricity & Magnetism Maxwell’s prediction of many kinds of electromagnetic radiation

Energy Transfer by Waves Carry energy Matter doesn’t move Properties of Waves Wavelength Frequency Velocity Amplitude

The Relationship Among Wavelength, Frequency, and Velocity velocity of a wave = wavelength x frequency

Properties of Electromagnetic Waves Wavelength (e.g. crest to crest) – Any value Frequency (number per second) – Any value Speed = 300,000 kilometers per second = 186,000 miles per second Amplitude (height of the wave)

Electromagnetic Spectrum Diagram of EM spectrum (w/ color)

Properties of Electromagnetic Waves Relationship between short & long waves Short waves = high frequency = high energy Long waves = low frequency = low energy Matter interacts with light in 3 ways: Transparent – light passes through Absorbing – matter soaks up energy Scattering – light bounces off

Some Matter is Transparent to Light Light waves pass through transparent materials

Some Matter Absorbs Light Light waves are absorbed: Materials soak up energy

Some Matter Scatters Light Light waves hit and bounce off in many directions

Scattering (Reflection)

Scattering (Refraction)

Electromagnetic Spectrum Diagram of EM spectrum (w/ color)

Radio waves Produced when electrons accelerate Amplitude increases with amplifier power Most everyday objects are transparent to radio waves Walls, ceiling, windows, doors Metals absorb radio waves That’s why antennas are made of metal What scatters radio waves? Ionosphere, especially at night

Radio Telescope

Amplitude Modulation (AM) Carrier waves Modulated signal by altering amplitude Analogous to turning a flashlight off and on

Frequency Modulation (FM) Carrier waves Modulated signal by altering frequency Analogous to switching a flashlight from yellow to blue

Electromagnetic Spectrum Diagram of EM spectrum (w/ color)

Microwaves 3 major uses in our society Cooking (Ovens)

Microwaves 3 major uses in our society Cell phones (point-to-point communications)

Microwaves 3 major uses in our society Radar (stealth technology)

Electromagnetic Spectrum Diagram of EM spectrum (w/ color)

Infrared Radiation (Heat)

Infrared Radiation (Heat)

Electromagnetic Spectrum Diagram of EM spectrum (w/ color)

Visible Light

Visible Light

Electromagnetic Spectrum Diagram of EM spectrum (w/ color)

Higher Energy Spectra (Potential Cell Damage) High energy = short wavelengths Ultraviolet radiation Sunblock

Higher Energy Spectra (Potential Cell Damage) High energy = short wavelengths X-Rays Medicine

Material Properties [NEXT WEEK] Atoms alone Structure Periodic Table Chemical Bonding Types of bonds Chemical Reactions Material Properties [NEXT WEEK] States of matter Mechanical & Electrical Properties

The atom GREAT IDEA: All matter is made of atoms which have a positively-charged nucleus surrounded by negatively-charged electrons. KEY WORDS: Atom Proton Neutron Electron Atomic Number Nucleus Ion Periodic Table of Elements

Are Atoms Real?

Evidence for Atoms 1. Behavior of gas 2. Ratios of elements

Evidence for Atoms 1. Behavior of gas 2. Ratios of elements 3. Radioactivity 4. Brownian Motion – Einstein

Evidence for Atoms 5. Avogadro's number (6.0221415 x 1023) 6. X-ray diffraction 7. Atomic microscopy

Is there something smaller? Electron (J. J. Thompson)

Is there something smaller? Electron (J. J. Thompson) Negatively charged Easily stripped off atoms Mass is negligible

Is there something smaller? Rutherford Scintillation Experiments

Is there something smaller? Rutherford Scintillation Experiments Atomic “bullets” hit gold foil A few bounce backwards Reveals tiny but massive atomic nucleus

Niels Bohr’s Model of the Atom

Niels Bohr’s Model of the Atom Electrons occur in fixed energy levels (shells)

Electron energy levels are analogous to standing waves Bohr Model of the Atom Electron energy levels are analogous to standing waves

Changes levels = Quantum leaps Photon = single light wave emitted Bohr Model of the Atom Changes levels = Quantum leaps Photon = single light wave emitted

Properties of Electromagnetic Waves Matter and light interact in three ways: Matter can be transparent to light. Matter can absorb light. Matter can scatter light.

Quantum Mechanics At the scale of atoms, everything comes in “quanta” (bundles). You can’t measure a property without changing the object being measured. Every measurement requires: A sample, A source of energy, A detector.

Absorption of Light

Is There Any Order to the Different Kinds of Atoms? Dimitri Mendeleev ca. 1867

Periodic Table of the Elements

Periodic Table of the Elements

Chemical Bonding Key Idea: Atoms link together by the rearrangement of their electrons 1. “Magic” numbers of electrons (i.e. 2, 10, 18 and 36) form very stable atoms. 2. Electrons may be transferred or shared to form stable bond 3. Ionic, metallic and covalent bonds

Periodic Table of the Elements

Ionic Bonding

Periodic Table of the Elements

Metallic Bonding

Periodic Table of the Elements

Covalent Bonding Hydrogen

Periodic Table of the Elements

Covalent Bonding WATER