CH 2 NOTES
Section 2.1
Matter: Are rocks, metal, glass and plastic made up of tiny solid
particles or mostly empty space?
What types of matter consist mostly of empty space?
Gas – more empty space between atoms than solids or liquids
Macro to sub-micro (see photo p. 50):
Evidence that air consists of invisible particles of matter.
Rock, metal, glass, and plastic are made up of similar particles!
DEMO: How small is matter?/Evidence of Alpha Particles
(Helium Nuclei with a positive charge)
Direct evidence that matter exists and is made up of smaller,
“unseen” particles.
ATOMS & THEIR STRUCTURE
Early Ideas: Greek Philosophers (2500 years ago) only observed
matter, but did not test their hypotheses with experiments... No
scientific model/method was followed.
Example: Piece of aluminum foil.
 How small can one cut the pieces of foil and still have
aluminum?
 If I continue to cut, will I no longer have aluminum, but
some other substance?
o Based on these simple observations (macro), the
Greeks had no problem hypothesizing about the
smallest particles of matter.
Democritus (460 – 370 B.C.) proposed that the world is made
up of empty space and tiny, invisible particles called atoms.
This introduced the atomic theory of matter.
Development of Modern Atomic Theory
Law of Conservation of Matter (Mass): Lavoisier (1782) observed
that in a sealed container, the mass of the reactants (ingredients) is
equal to the mass of the products in a chemical reaction ().
Law of Definite Proportions: Proust (1799) observed that the
elements that composed the compounds were always in a certain
proportion by mass.
Ex. Water is 11.2% hydrogen and 88.8% oxygen; see figure
2.3
Why is water only 11% hydrogen, if it contains 2 H atoms?
Ex. CO and CO2
C6H12O6 and C12H24O12
When two or more elements form a compound, the ratios of the
masses that combine can always be reduced to small whole
numbers.
Dalton’s Atomic Theory (1803)
1. All matter is made up of atoms.
2. Atoms are indestructible and cannot be divided into smaller
particles.
3. All atoms of one element are exactly alike, but are different
from atoms of other elements.
Combustion:
EXTRA CREDIT: What is phlogiston, and who suggested
it’s existence?
Recycling: See figure 2.4
Do trash compactors reduce waste? Garbage disposals?
Hypothesis, Theory, Law
 Hypothesis: a testable prediction to explain observations
 Theory: explanation based on many observations and
supported by results from many experiments.
 Law: can be observed to be true whether or not it can be
explained.
 See Figure 2.5, p. 59
ATOMIC STRUCTURE
J.J. Thomson discovered some inaccuracies to Dalton’s Theory:
An atom is made up of smaller particles and that atoms of the
same element can be nearly, but not exactly the same.
Cathode-Ray Tube: experiment led to discovery of electrons,
invisible, negatively changed, subatomic particles.
DEMO: Cathode Ray Tube
How does reason tell you that the atom isn’t just made up of
electrons?
Protons: positively charged subatomic particles, with a mass
much greater than the electron.
Thomson discovered that neon consisted of atoms of two different
masses. These are called isotopes: atoms of an element that are
chemically alike, but differ in mass.
Neutrons: neutrally charged subatomic particles with mass
equal to a proton.
Apply this Chemistry: How does fabric softener work?
How are these particles arranged?
Thomson’s chocolate chip cookie dough (Plum Pudding)
v. Nagaoka’s planetary model?
Neither was completely correct!
Rutherford’s Gold Foil Experiment (1909)
 DEMO: See Figure 2.9
 Results led to a new model of the atom:
o The atom has a small, dense, positively charged core,
called a nucleus, BUT the atom was made up of mostly
empty space.
If an atom is so small, then there must be lots of them... how do we
work with such large numbers?
See page 795 for work on Scientific Notation
ATOMIC NUMBER AND MASSES
Atomic Number: the number of protons that determines the
identity of an element.
Mass Number: the sum of the protons and neutrons in the
nucleus of an atom.
Atomic Mass: average of ALL isotopes of the element.
Section 2.2
ELECTRONS IN MOTION (1913)
Niels Bohr: Danish Scientist who suggested that electrons have
enough energy to keep them from being pulled towards the
positive nucleus... Much like a satellite in orbit. However,
electrons only occupy “orbits” of certain amounts of energy.
This “orbit” model of the atom is only an analogy! Electron
motion is very irregular, and an electron may be very close to the
nucleus at times.
n=1
n=2
n=3
WHAT IS UNCERTAINTY?
 It is impossible to measure exactly both the position and the
momentum (mass & speed) of an object (electron)
o Ex. moving fan
ELECTROMAGNETIC SPECTRUM
The entire range of the electromagnetic radiation that includes
many forms of radiant energy that travel in waves having both
electrical and magnetic properties
 Is this considered matter?
Waves:
a. Transfer energy
b. Are produced by something moving back and forth
c. Have frequency (Hz) and wavelength (nm)
d. ALL electromagnetic waves travel at the speed of light:
3.00  108 m/s
What is the relationship between wavelength, frequency and
energy?
Examples: radio waves, microwaves, x-rays, ultraviolet waves,
visible light waves, infrared waves
See Figure 2.19
ELECTRONS AND LIGHT
DEMO: How do electrons emit light? (6 “salt” compounds)
Emission Spectrum: the spectrum of light released from excited
atoms of an element.
1.
2.
3.
4.
Electrons absorb energy
Electrons move to a higher energy level
Electrons “fall back” to a lower energy level
Energy is emitted in the form of light that results in specific
colors of light for each element (R.O.Y.G.B.I.V.)
The higher the level, the greater the amount of energy emitted...
book analogy.
MiniLab 2, p.77: Line Emission Spectra of Elements
 Record observations and answer analysis questions in your
notebook.
 Please complete questions 1 through 3!
Energy Levels: regions of space in which electrons can move about
the nucleus of an atom. Like rungs on a ladder... but not evenly
spaced! Every element is unique ~ this includes the distances
between the levels with each atom. No two are exactly alike.
ELECTRON CLOUD MODEL (Around 1926)
 Because we cannot pinpoint exactly where an electron is on
the “surface” of an atom, we refer to its positions as an
electron cloud. Think of the moving fan!
 This cloud is a spherical region around the nucleus where the
electrons travel.
The chemical behavior of any 2 substances is determined by the #
and arrangement of these electrons around the nucleus!
Each energy level can hold a limited number of electrons:
1st: holds max of 2, closest to the nucleus
2nd: holds max of 8
3rd: holds max of 18
4th : holds max of 32
Rule: calculate the max # of electrons using the equation 2n2,
where n is the energy level
 Try calculating the max for the forth energy level.
* There are many more Energy Levels that we will use in Ch. 4 *
Valence Electrons: electrons in the outermost energy level.
These are the electrons that will interact when in the presence of
another atom! They are pretty important!
 Predict the # of valence electrons in Groups (columns)
1, 2, 13, 14, 15, 16, 17 and 18 on the Periodic Table.
Lewis Dot Diagrams: an illustration of the valence electrons of an
atom that surround the chemical symbol of the element.
 Let’s do some examples on the board!