Looking back at Earth from orbit of Saturn(Voyager)

A blue water planet with 30% reflectivity (clouds, ice, snow)

About as many stars in the observableuniverse as the number of grainsof dry sand on allthe beaches of world.

Carl Sagan

~100 billion galaxies, each with ~100 billion stars, so N ~1022

Compare: number of H2O molecules in 1 ml of water, or about N = 3 x1022

Russian Chemist Dmitri Mendeleev

Early periodic table

The Periodic Table of Chemical Elements

A different way to view the periodic table

Net reaction: 4 protons (H) fuse to make a helium (He) nucleus, releasing energy: ~0.7% mass converted to

energy by ∆E = mc2

What keeps the sun shining??

The Crab Nebula:remnant from supernova explosion, observed in 1054 A.D.

Left behind: a pulsar, spinning neutron star.

SN explosions, the only way to make the elements beyond iron (Fe).

Relative atomicabundances in thegalaxy, normalized to Hydrogen (H =1.00).

Universe is still ~98%(H, He), as forged in the first minutes of theBig Bang.

Notice the Fe ‘hill’ of higher abundance (most stable nucleus)

Why might acarbon-based life, with H2O solvent be expected elsewhere?

The mass of atoms is in the nucleus, the size of an atom is the size of the electron ‘cloud’ (Heisenberg Uncertainty Principle)

The structure of atoms with ~all mass in the nucleus (protonsand neutrons), surrounded by a cloud of electrons

Rutherford’s experiment

showed that the massof atoms wasconcentrated in a very small nucleus.

Bohr with Heisenberg (discussing the ‘critical mass’ for fission?)

Niels Bohr (early model of H atom)

Albert Einstein(photo-electric effect)

Naming atoms

Proton number defines the element

Isotopes have different numbersof neutrons for thesame number ofprotons (same element)

Electromagnetic radiation travels at the speed of light (c)

Photons have no mass Energy is proportional to frequency of the radiation

(Wavelength) times (frequency) = speed of propagation = c

The electromagnetic spectrum by wavelength

Electromagnetic energy is directly proportional to the frequency, and inversely proportional to wavelength

Photon Emission

System drops from a higher energy level to a lower one by spontaneously emitting a photon.

Emission

“Continuous” spectrum “Quantized” spectrum

Any E ispossible

Only certain E are ‘allowed’transitions

E E

White light can be spread into a rainbow of differentwavelengths (colors) by a prism or grating (Newton)

Emission spectrum of atomic H

Light Bulb:Continuous spectrum

Hydrogen Lamp:Discrete lines only

Quantized, not continuous

The spectrum of molecular hydrogen H2: a very complex pattern of emission lines unique to this species (‘fingerprint’)

Spectral lines correspond to electron jumps between discrete (’quantized’) energy levels of atoms, ions, and molecules