1. Atoms, Molecules & Ions
AP Chemistry

2. Notable Scientists & Laws
Robert Boyle, English, first “chemist” to perform quantitative experiments of pressure versus volume. -developed a working definition for elements”. Antione Lavoisier, French, , -published the first modern chemistry textbook -was the first to insist on quantitative experimentation. -verified the Law of Conservation of Mass: Mass is neither created nor destroyed.

3. Joseph Proust, French,
-stated the Law of Definite Proportions (once called
Proust’s law):
A given compound always contains exactly the
same proportion of elements by mass
John Dalton, English,
-stated the Law of Multiple Proportions:
When two elements combine to form a series of
compounds, the ratios of the masses of the second
element that combine with 1 gram of the first
element can always be reduced to small whole
numbers.

4. Mass of Oxygen that combines with 1 gram of Carbon Compound I 1
Mass of Oxygen that combines with 1 gram of Carbon Compound I 1.33 g Compound II 2.66 g Therefore Compound I may be CO while Compound II may be CO2. -compound II has 2x the number of O’s as compound 1 I = 1.33g = 1 II 2.66g 2

5. John Dalton, English, developed his Atomic Theory in 1808 (p46) Joseph Gay-Lussac, French, in 1809, performed experiments [at constant T & P] to measure volumes of gases that react with each other.

6. Amadeo Avogardro, Italian, 1776-1856
-in 1811, proposed his hypothesis regarding Gay-
Lussac’s work (Avogadro’s Hypothesis)
At the same temperature and pressure, equal volumes
of different gases contain the same number of particles.
-was basically ignored, so 50 years of confusion followed

7. Gay-Lussac and Avagadro’s experimental work held the keys to determining absolute formulas for compounds, which Dalton was unable to do.
-it was Dalton’s incorrect assumptions about formulas of
certain compounds that had him incorrectly calculating
atomic masses
-more research was done on the concept of atoms
eventually leading to the:
**MODIFICATIONS TO DALTON' S THEORY**
1. Subatomic particles were discovered.
2. Isotopes were discovered.

8. Characterizing an Atom
The Electron J.J. Thomson, English (during ) -discovered the cathode ray, a negative particle we now call an electron

9. Characterizing an Atom
Thomson, cont. -measured the charge-to-mass ratio e = -1.76x108 C m g where e is charge on electron in Coulombs, (C) and m is its mass in grams. -repeated experiments found all metals, and atoms, contained electrons

10. Thomson, cont. -all atoms were neutral ∴ there must be some (+) charge within the atom and the “plum pudding” model was born.

11. Robert Millikan, American, during oil drop experiment -calculated the mass of an electron by determining the size of the electron charge and using the mass-to-charge ratio discovered by Thomson mass of e- = 9.11 × kg,

12. Ernest Rutherford, England, in pioneer in radioactive studies -tested Thomson’s plum pudding model -if Thomson was correct, the massive α particles would pass through the gold foil with only occasional deflections.

13. Ernest Rutherford, cont
Ernest Rutherford, cont. -was astounded when many particles bounced back or were deflected -determined the plumb pudding model was incorrect -for the (+) a particles to be deflected or reflected, there must be a (+) core he called the nucleus - (+) core contains most of the atom’s mass -nuclear atom was born

14. Modern View of Atomic Structure
Element: matter composed of only one type of atom Atom: smallest particle that retains the chemical properties of that element • nucleus-- protons and neutrons; very dense - proton--positive charge, defines atomic number - neutron--no charge, same size & mass as a proton, alters mass number • electron--negative charge, responsible for bonding, located outside the nucleus.

15. X atomic number  Z mass number  A  element
isotope: atom with the same number of protons but different number of neutrons
-12C, 13C, 14C
-most elements contains mixtures of isotopes
 element