THE ATOM!THE ATOM!BUILDING BLOCKS OF MATTERBUILDING BLOCKS OF MATTER

Rutherford!Rutherford!

►The gold foil experimentThe gold foil experiment►Shot alpha particles (helium nuclei) at Shot alpha particles (helium nuclei) at

gold foilgold foil

4Mass numberMass number

chargecharge

2+

0.3% of the time the alpha particle bounced back

2.7% of the time the alpha particle was deflected

97% of the time the alpha particle went straight through

Lead box containing alpha Lead box containing alpha particle sourceparticle source

Gold foilGold foil

Scintillation Scintillation screenscreen

Turn foil so you are looking at the edge. Then magnify!

Cross section of gold foil (Magnified x1012)

Alp

ha p

artic

le

Alp

ha p

artic

le

sou

rce

sou

rce

Rutherford’s ResultsRutherford’s Results►Most of the atom is?Most of the atom is?

Empty spaceEmpty space

► In the center of the atom is?In the center of the atom is? NucleusNucleus

►With a charge of ?With a charge of ? Positive (due to Positive (due to PROTONSPROTONS, the second , the second

particle)particle)

The Third ParticleThe Third Particle►Rutherford’s co-Rutherford’s co-worker James worker James Chadwick discovered Chadwick discovered the NEUTRON!the NEUTRON!

►The NEUTRON has a The NEUTRON has a ________charge.________charge.NEUTRALNEUTRAL

If its mostly empty space then how are things solid?

1Protons and 1Neutron1Protons and 1Neutron

Relative Mass: Animal analogyRelative Mass: Animal analogy

1 amu(atomic mass unit)

2 amu(atomic mass unit)

p+n0

Properties of Subatomic Properties of Subatomic ParticlesParticles

ParticleParticle SymbolSymbol LocationLocation ChargeCharge Mass Mass (amu)(amu)

ElectronElectron ee-- Electron Electron CloudCloud

NegativNegativee

11

18401840

ProtonProton pp++ NucleusNucleus PositivePositive 11

NeutronNeutron nn00 NucleusNucleus NeutralNeutral 11

Atomic NumberAtomic Number

Atomic Number Atomic Number ==

# of Protons =# of Protons =

# of Electrons # of Electrons ==

PracticePracticeWrite down the symbol, NAME, atomic number, Write down the symbol, NAME, atomic number,

protons,protons,and electrons for the following.and electrons for the following.

1.1. WW2.2. AuAu3.3. UU4.4. FrFr5.5. DyDy6.6. 34 p34 p++

7.7. 100 e100 e--

8.8. Atomic number 11Atomic number 119.9. 50 p50 p++

10.10. 47 e47 e--