staar ladder to success rung 2. john dalton dalton’s four postulates 1.elements are composed of...

STAAR Ladder to Success

Rung 2

John Dalton

Dalton’s Four Postulates

1. Elements are composed of small indivisible particles called atoms.

2. Atoms of the same element are identical. Atoms of different elements are different.

3. Atoms of different elements combine together in simple proportions to create a compound.

4. In a chemical reaction, atoms are rearranged, but not changed.

J. J. Thomson (1903)

• Cathode Ray Tube Experiments– beam of negative particles

• Discovered Electrons– negative particles within the

atom

• Plum-pudding Model

Ernest Rutherford (1911)

• Gold Foil Experiment

• Discovered the nucleus– dense, positive charge in the

center of the atom

• Nuclear Model

Niels Bohr (1913)

• Energy Levels– electrons can only exist in

specific energy states

Erwin Schrödinger (1926)

Electron Cloud Model (orbital)• dots represent probability of finding an e-

not actual electrons

EM Spectrum

LOW

ENERGY

HIGH

ENERGY

R O Y G. B I V

red orange yellow green blue indigo violet

Calculations

• Example #1:If a particular green light has a wavelength of 4.9 x 10-7 m, what is its frequency?

• Example #2:The human eye can see light with a frequency about as high as 7.9 x 1014 Hz, which appears violet. Calculate the energy that one photon of violet light carries.

• Example #3:Find the energy of violet light if the wavelength is 4 x 10-7 m.

Isotopes

• Atoms of the same element with different numbers of neutrons.

C126Mass

Atomic #

• Isotope symbol:

“Carbon-12”

Average Atomic Mass

• weighted average of all isotopes• on the Periodic Table• round to whole number

100

(%)(mass(mass)(%) )

Avg.AtomicMass

Avg.AtomicMass

Average Atomic Mass

• EX: Calculate the avg. atomic mass of oxygen if its abundance in nature is 99.76% 16O, 0.04% 17O, and 0.20% 18O.

100

(18)(0.20)(17)(0.04))(16)(99.76 16.00amu

The Orbitals

sp d

f

© 1998 by Harcourt Brace & Company

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Periodic Patterns

Lewis Dot Diagrams

• Dots represent the valence e-.• EX: Sodium • EX: Chlorine