What do the following have in common?

What do the following have in common?

Scientific Modeling

• Makes scientific concepts easier to understand or visualize by referencing common knowledge

• Can you think of any scientific models?

Scientific Models

Scientific Models

Models of the Atom

History of the Atom

Jigsaw Activity

• Number off 1-5 (4 groups of 5, 1 group of 6)

• Each group will be responsible for a section of the atomic theory from Hebden p.139-144

• As a group, you must fully understand your section because each member will be teaching it to the rest of the class individually

Jigsaw Activity

• Group A: each member will teach the rest of the class about “Early Models of the Atom”

• Group B: each member will teach the rest of the class about “Dalton’s Atomic Theory”

• Group C: each member will teach the rest of the class about “The Thomson Model”

• Group D: each member will teach the rest of the class about “The Rutherford Model”

• Group E: each member will teach the rest of the class about “The Bohr Model"

Jigsaw Activity

• 10 min to read & make notes on the section you’re responsible for

• Then, all the 1s, 2s, etc. will form groups and teach new group members about their section (like piecing together a jigsaw puzzle)

• Each member presents 2 min on their topic starting with group A

Early Models of the Atom

• 5th century BC - Leucippus & Democritus– Atoms are tiny, uncuttable particles – Properties are direct results of differences in size

& shape of atoms

Early Models of the Atom

• 4th century BC – Aristotle– Matter had no properties on its own– Properties came from different combinations– 4 elements: water, air, fire, earth

Dalton’s Atomic Theory

Law of Definite Proportions• E.g. 2/18 of the mass of H2O is always from H and

16/18 is from OLaw of Multiple Proportions • Compounds are made of atoms in whole number

ratios • E.g. H & O can make OH-, H2O, H3O+, H2O2

Law of Conservation of Mass• Mass of reactants = mass of products

Thomson’s Model of the Atom

• Discovered + and - particles in atoms • Proposed “plum pudding” model: negatively

charged raisins spread around positively charged bread

Rutherford Model of the Atom

Gold Foil Experiment• Fired alpha (He2+) particles at thin gold foil• Thomson model predicts minimal deflection of

alpha particles b/c + charge spread out• Rutherford found small fraction of particles w/

significant deflection• Concluded + charges must be concentrated in

a small area w/in atoms

Rutherford Model of the Atom

Bohr’s “Planetary” Model

• Electrons orbit around nucleus at specific energy levels

• Been disproven but many key ideas still apply to the modern model of the atom

Heisenberg’s “Cloud” Model

• Heisenberg’s Uncertainty Principle: σxσp ≥ ħ/2• The more precisely you know the position of

an electron, the less precisely you know the momentum and vice versa

• Can’t know both at the same time so the position of electrons can only be in terms of probability