Everything You Need To Know About Atoms (for this course)

Tiny Bits Before we talk about what atoms are made of and what they can do, you must know: Before we talk about what atoms are made of and what they can do, you must know: They are VERY light, They are VERY light, They are VERY small, They are VERY small, There are VAST numbers of them. There are VAST numbers of them.

Bromide Atoms

Hydrogen on Graphene

Crystal Lattice

Photograph of a Single Molecule of Pentacene, used in solar cells 14 Carbon and 22 Hydrogen atoms

Biggest Tiny Parts Neutrons: N, heaviest, no electrical charge Neutrons: N, heaviest, no electrical charge Protons: P +, slightly less heavy, positive electrical charge Protons: P +, slightly less heavy, positive electrical charge Electrons: e -, much lighter than neutrons or protons, negative electric charge Electrons: e -, much lighter than neutrons or protons, negative electric charge All three have a quantum mechanical quality called spin 1 / 2 All three have a quantum mechanical quality called spin 1 / 2

Smaller Tiny Parts Neutrinos: Neutrinos: Three kinds: electron e, muon , tau  Three kinds: electron e, muon , tau  Weakly interactive Weakly interactive VERY low mass, no charge VERY low mass, no charge Travel at the speed of light Travel at the speed of light (We’ll use these a little later) (We’ll use these a little later)

Atoms Atoms have protons and electrons and, with one exception, neutrons Atoms have protons and electrons and, with one exception, neutrons The simplest atom is hydrogen The simplest atom is hydrogen 75% of the universe is hydrogen 75% of the universe is hydrogen

Flavors (Isotopes) of Hydrogen: Deuterium (D) Tritium (T)

Helium Two electrons, two protons, two neutrons Two electrons, two protons, two neutrons 24% of the Universe 24% of the Universe (There is a flavor with only one neutron) (There is a flavor with only one neutron)

As of June 2011, 114 different elements… But hydrogen (H) and helium (He) are all we need for the most part But hydrogen (H) and helium (He) are all we need for the most part

straP yniT tseggiB Antimatter! Antimatter! Negative protons, positive electrons Negative protons, positive electrons Antineutrons more difficult to explain (antiquarks, CPT symmetry—not really necessary for our study) Antineutrons more difficult to explain (antiquarks, CPT symmetry—not really necessary for our study) When matter meets antimatter: annihilation! When matter meets antimatter: annihilation! (We’ll meet this later also) (We’ll meet this later also)

PET Scan Positron emission tomography

It Takes Energy To: Remove an electron from an atom: Remove an electron from an atom: Jam a proton and neutron together to make deuterium (D) Jam a proton and neutron together to make deuterium (D) Jam an N and a D together to make a tritium (T) Jam an N and a D together to make a tritium (T) Jam two Ts together to get He Jam two Ts together to get He

E=mc 2 Except for reactions that involve only electrons, nuclear processes are governed by that famous equation Except for reactions that involve only electrons, nuclear processes are governed by that famous equation It says that matter can be converted to lots of energy, and that energy can be transformed into matter It says that matter can be converted to lots of energy, and that energy can be transformed into matter Making He out of H takes a lot of energy, but once it’s accomplished, you get more energy back Making He out of H takes a lot of energy, but once it’s accomplished, you get more energy back

Fusion That last process is a form of fusion That last process is a form of fusion Not to be confused with fission (taught in another course) Not to be confused with fission (taught in another course) The reaction can be notated this way: The reaction can be notated this way: T + T -> 4 He + 2N I will use this shorthand later on ( and remind you of what it means ) I will use this shorthand later on ( and remind you of what it means )

Other Examples A reaction can emit energy in the form of a photon A reaction can emit energy in the form of a photon D + D -> 4 He +  A reaction can generate a neutrino A reaction can generate a neutrino P + + P + -> D + e + + e Don’t memorize these! They are just examples !

And that’s all you need to know about atoms!