1. Lecture 2: Atoms, isotopes, ions & molecules
Topics Brown, chapter 2
1. Dalton’s Atomic Theory
Four postulates
2. Molecules & formulas
Molecular vs. empirical
3. Discovery of atomic structure
Subatomic particles
Radioactivity
Nuclear atom
4. Sub-atomic particles & the periodic table
Atomic number & mass
Isotopes
5. Atomic weights
Average atomic mass
Mass spectroscopy
6. Periodic table
7. Ions & ionic compounds
Ionic charges
8. Naming chemical compounds
Ionic compounds (salts), molecular compounds, & acids
“Grey” topics will be covered next week. Labor day has made this week bit short for a full chapter.

2. Atoms are the fundamental unit of chemistry.
Atoms combine to form molecules.
Atoms have subatomic particles & a nucleus.
Each element has a distinct number of protons.
The general process of advancing scientific knowledge by making experimental observations and by formulating hypotheses, theories, and laws.
It’s a systematic problems solving process AND it’s hands-on….. Experiments must be done, data generated, conclusions made.
This method is “iterative”; it requires looping back and starting over if needed. [Why do you think they call it REsearch?] Often years, decades or more of experiments are required to prove a theory.
While it’s possible to prove a hypothesis wrong, it’s actually NOT possible to absolutely prove a hypothesis correct as the outcome may have had a cause that the scientist hasn’t considered.

3. Our entire world is built from 100 elements
Chapter 2 focuses on:
The nature of the atom
How elements differ from one another
Why atoms combine & interact
How molecules are formed
Atoms are the fundamental building block of matter.
An element is a particular type of atom & is the smallest part of matter that retains distinct physical & chemical properties.
IBM spelled out in xenon electron clouds on a nickel surface (IBM Labs)
p.36-7

4. History of the atom p.38 Bohr (1913) Schrödinger (1926)
fire earth water air
Electrons orbit the nucleus at specific levels, or orbits.
Quantum theory: electrons occupy ‘ortitals’
Orbitals are wave -functions.
‘A-tomos’
Bohr (1913)
Schrödinger (1926)
Greeks - Democritus (~500 B.C.)
Dalton (1803)
Matter consists of particles called atoms.
Rutherford Thompson Millikan ( )
Pauli (1924)
The history of the atom is a long one, dating back to hypotheses formed by Greeks before the birth of Christ. The Greeks lacked the equipment and experimental insights to prove the existence of the atom.
Proof was finally provided by the English scientist, John Dalton, in Dalton’s proof came from experiments involving burning of metals in oxygen, and the use of accurate scales or balances.
Dalton’s work explained how and why several scientific laws, already accepted at the time, worked.
‘exclusion principle’
No more than 2 electrons may occupy the same orbital.
Atoms consist of subatomic particles: electrons, neutrons protons.
2 electrons in the same orbital have opposite ‘spin’.
p.38

5. Dalton’s Atomic Theory (1803)
Dalton’s experiments led to a proven Atomic Theory that is
best explained by stating its four postulates:
Each element is made up of tiny particles called atoms.
All atoms of a single element are identical to one another. And atoms of different elements differ from one another.
Chemical reactions don’t change atoms. (atoms are not created or destroyed by chemical reactions.)
Compounds (molecules) are formed when atoms combine at constant ratios.
Dalton believed that atoms were the smallest indivisible form of matter.
Dalton’s postulates helped to explain how two known laws worked:
Law of Constant Composition - Molecules are atoms atoms combined at constant (invariant) ratios of whole numbers.
Law of Conservation of Mass - All mass in our universe is conserved; neither created nor destroyed.
Dalton developed the Law of Multiple Proportions - Two atoms (A&B) can be combined to form many different molecules.
Each molecule will have a unique ratio of atoms A & B; ratios will be small whole numbers.
Examples? H2O, H2O2, OH-1
Which of these postulates is/are no longer thought to be true?
Law of Constant Composition
Law of Conservation of Mass
Dalton used his theory to develop another law:
Law of Multiple Proportions
p.38-9

6. Law of Multiple Proportions
Dalton used his theory to develop another law: the Law of Multiple Proportions
Two elements can be combined to form a wide variety of different molecules when combined at different ratios. The ratios are described by small whole numbers.
Let’s play with N (nitrogen) & O (0xygen):
N2O
NO2
N2O2
N2O4
N4O
What are the molecular formulas of the molecules shown above?
Can you think of other examples?
CO & CO2
CH4, C2H8, C3H6
OH-1, H2O, H2O2 – Here you can see how different the molecules are. Water is essential to life while hydrogen peroxide destroys life!
p.38-9