Everything You Need To Everything You Need To Know About AtomsKnow About Atoms

(for this course)(for this course)

Tiny BitsTiny Bits

Before we talk about what atoms are Before we talk about what atoms are made of and what they can do, you made of and what they can do, you must know: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 AtomsBromide Atoms

Hydrogen on GrapheneHydrogen on Graphene

Crystal LatticeCrystal Lattice

Photograph of a Single Photograph of a Single Molecule of Pentacene, used in Molecule of Pentacene, used in

solar cellssolar cells

14 Carbon and 22 Hydrogen atoms

Biggest Tiny PartsBiggest Tiny Parts

Neutrons: N, heaviest, no electrical Neutrons: N, heaviest, no electrical chargecharge

Protons: PProtons: P++,, slightly less heavy, positive slightly less heavy, positive electrical chargeelectrical charge

Electrons: eElectrons: e--, much lighter than neutrons , much lighter than neutrons or protons, negative electric chargeor protons, negative electric charge

All three have a quantum mechanical All three have a quantum mechanical quality called spin quality called spin 11//22

Smaller Tiny PartsSmaller Tiny Parts

Neutrinos: Neutrinos: Three kinds: electron Three kinds: electron ee, muon , muon , tau , tau

Weakly interactiveWeakly interactive VERY low mass, no chargeVERY low mass, no charge Travel at the speed of lightTravel at the speed of light (We’ll use these a little later)(We’ll use these a little later)

AtomsAtoms

Atoms have protons Atoms have protons and electrons and, and electrons and, with one exception, with one exception, neutronsneutrons

The simplest atom The simplest atom is hydrogenis hydrogen

75% of the universe 75% of the universe is hydrogenis hydrogen

Flavors (Flavors (IsotopesIsotopes) of Hydrogen:) of Hydrogen:Deuterium (D)--------Tritium (T)Deuterium (D)--------Tritium (T)

HeliumHelium

Two electrons, two Two electrons, two protons, two protons, two neutronsneutrons

24% of the 24% of the UniverseUniverse

(There is a flavor (There is a flavor with only one with only one neutron)neutron)

As of June 2011, 114 different As of June 2011, 114 different elements…elements…

But hydrogen (H) and helium (He) are all But hydrogen (H) and helium (He) are all we need for the most partwe need for the most part

straP yniT tseggiBstraP yniT tseggiB

Antimatter!Antimatter! Negative protons, positive electronsNegative protons, positive electrons Antineutrons more difficult to explain Antineutrons more difficult to explain

(antiquarks, CPT symmetry—not really necessary (antiquarks, CPT symmetry—not really necessary for our study)for our study)

When matter meets antimatter: When matter meets antimatter: annihilation!annihilation!

(We’ll meet this later also)(We’ll meet this later also)

PET ScanPET Scan

Positron emission Positron emission tomographytomography

It Takes Energy To:It Takes Energy To:

Remove an electron from an atom:Remove an electron from an atom: Jam a proton and neutron together to Jam a proton and neutron together to

make deuterium (D)make deuterium (D) Jam an N and a D together to make a Jam an N and a D together to make a

tritium (T)tritium (T) Jam two Ts together to get HeJam two Ts together to get He

E=mcE=mc22

Except for reactions that involve only Except for reactions that involve only electrons, nuclear processes are governed electrons, nuclear processes are governed by that famous equationby that famous equation

It says that matter can be converted to It says that matter can be converted to lotslots of energy, and that energy can be of energy, and that energy can be transformed into mattertransformed into matter

Making He out of H takes a lot of energy, Making He out of H takes a lot of energy, but once it’s accomplished, you get more but once it’s accomplished, you get more energy backenergy back

FusionFusion

That last process is a form of That last process is a form of fusionfusion Not to be confused with fission (taught Not to be confused with fission (taught

in another course)in another course) The reaction can be notated this way:The reaction can be notated this way:

T + T -> T + T -> 44He + 2NHe + 2N I will use this shorthand later on (I will use this shorthand later on (and and

remind you of what it meansremind you of what it means))

Other ExamplesOther Examples

A reaction can emit energy in the A reaction can emit energy in the form of a photonform of a photon

D + D -> D + D -> 44He + He + A reaction can generate a neutrinoA reaction can generate a neutrino

PP++ + P + P++ -> D + e -> D + e++ + + ee

Don’t memorize these! They are just examplesDon’t memorize these! They are just examples!!

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