1. Scientific Laws and Theories

2. Law vs. Theory Law Theory Everyday language Science Everyday language
Rules
Science
What happens
Measurable pattern
Everyday language
A judgment, guess, or opinion
Science
Why it happens
An explanation of data

3. Early Laws Law of Conservation of mass:
Mass of reactants = mass of products
Baking Soda Reacts with Vinegar in a closed container
Trial
Baking Soda
Vinegar
Products & Excess #1
5.7 g
8.2 g
13.9 g #2
2.3 g
1.7 g
4.0 g

4. Early Laws Law of Definite Proportions:
The mass ratios of elements in a given compound are always equal.
Reaction of Mg with O2 gas data:
Trials
Trial #1
Trial #2
Trial #3
Mg reacted (g)
12.15
4.86
339
O2 reacted (g) 16
6.4
441

5. Atomic Theories Dalton’s Atomic Theory
Based on Laws of Cons of Mass, Law of Definite Proportions, and other Laws …
1) Each element composed of indivisible particles (atoms)
2) All atoms of same element identical; of different element are different.
3) Atoms can not change, only rearranged into different combinations (compounds) during chemical reaction.

6. Atomic Theories Thomson’s Atomic Theory (Plum Pudding Model)
Based on Experiments with a Cathode Ray Tube
Determined Rays must have charge.
Determined Atom can be broken into charged particles, but overall charge of atom is neutral.

7. Atomic Theories Rutherford’s Atomic Theory (Nuclear Model)
Based on Experiments with Gold Foil
Determined most of the atom is empty space
Tiny Dense nucleus

8. Atomic Theories Bohr’s Atomic Theory (Planetary Model)
Based on Line Spectra of Elements
Believed that different electrons rotate around the nucleus in different energy orbits

9. Atomic Theories Modern Atomic Theory (Quantum Model)
Based on Quantum Mechanics
Electrons move randomly in “orbitals”
They do not revolve around the nucleus like planets revolve around the sun.

10. Atomic Theories Isotopes Mass Spectrometer
Not all atoms of the same element are identical.