Download Notes Ch 4.1 and 4.2

Warm-up
On your group white board describe an
atom: structure, components etc
You can use drawings (labels!) or words

Atomic Model Theory and
how it evolved
Video

timeline of discoveries
How scientific theories and
models evolve….
science is a process
 many scientists contribute to it
 the model changes over time
 the model will change in the future as
more research leads to new discoveries

400 BC Democritus
Invented the word!
Atom
“The smallest particle of matter is
indivisible and indestructible and I will
call it “atomos” (atom)
John Dalton 1802
isolated 20 pure substances
 he called them “elements” and gave them
name, symbols and weights
 Made the first periodic table
 The first atomic theory

1st atomic Theory:
1. Matter is made up of atoms: tiny,
indivisible
 2. Atoms of the same element are identical
and different from other elements.
 3. Chemical Rx: atoms can be joined into
compounds, separated or rearranged

Subatomic Particle Discovery
JJ. Thompson’s 1897 - Cathode Ray
experiment
Key Experiments: Cathode Ray
Machine
Cathode: negative electrode Anode:
positive electrode
Observation:
cathode ray beam is attracted to a positive
pole and rejected by a negative pole
Conclusion:
The beam is composed of ____________
charged particles
Thompson called them Electrons
New Atomic Model
Plum Pudding Model
Electrons are embedded in a positively
charged matrix and they are overall neutral
Goldfoil Experiment
1917 Rutherford: “Blasted” ultra thin gold foil
with Alpha particles (nuclei)
Theory: alpha particles should go straight
through the plum pudding.
Goldfoil/Alpha particle Machine
Observation: most go through but a few
get deflected at odd angles???
What’s in the center of an
atom?
There is something hard, impenetrable in an
atom that deflects alpha particles
Solar System Model

Solar System Model – nucleus in the
center, electrons orbiting like “planets”
Atoms are mostly empty
space containing
negative electrons
there is a small, dense
positively charged
nucleus in the center
Quantum Mechanical/Bohr’s
Model

Niels Bohr and Max Planck 1920’s
What’s a quantum?
Theory:
Electrons occupy distinct energy levels.
They can move up or down levels by
releasing or absorbing energy units called
quantums
Warm-up
Sketch Thompson’s experimental set up
and explain how he concluded that the
Cathode Ray was negatively charged
 Sketch Rutherford’s experimental set up
and explain how he determined that an
atom is mostly empty space but has a
small hard nucleus

Current Atomic Model
Nucleus
Electron Orbital
Clouds
Current Atomic Model Summary
Nucleus: small, dense, contains defined numbers of
 protons: p+ ,positive charge, mass: 1 amu
 neutrons: no , neutral charge, mass: 1 amu
Number of p+ and no in the nucleus can only be
changed in a nuclear reaction
Space surrounding nucleus: contains
 Electrons: e-, negative charge, “no mass”
 are in constant, extremely fast motion
 Occupy special shaped orbital clouds
 Can be easily removed (electricity), added
(ions) or rearranged (chemical Rx)
Size and Mass of Atoms
Size : measured in Ångstrǿm:
1Å=1.0 x10-11m
Mass: measured in atomic mass units:
1 amu = 1/12th of the mass of a Carbon-12
atom = 1.64 x 10-24 grams
 Some electrons do orbit in spherical
motion, others in dumbbell shaped clouds
Practice
What is the mass in amu of 45
Protons?
45 amu
2. What is the mass in gram of 45
Protons?
45 x 1.64 x 10-24 g = 73.8 x 10-24 g
7.38 x 10-23 g
1.
Practice
3. What is the mass of an element with 5
protons and 7 neutrons?
12 amu
4. What is the size of an element with a
width of 45 Ångstrøm in meters?
45 x 1.0 x 10-11 m= 45 x 10-11m =
4.5 x 10 -10 m
5. Calculate mass and charge of
an element with
A. 8 protons, 8 neutrons and 10 electrons?
16 amu, 2B. 15 protons, 17 neutrons, 18 electrons
32 amu, 3C. 12 protons, 13 neutrons, 10 electrons
25 amu, 2+
D. 6 protons, 8 neutrons, 6 electrons
14 amu, 0
Warmup
1. What is the mass in amu’s of an element
with 33 protons and 37 neutrons?
2. Name the element.
3. What is the mass in grams of an element
weighing 23.5 amu’s?
4. What size in meters does an element
with 1078 Angstrom have?
Journal
1. Name the element of the three isotopes
shown below
2. Write the two short hands
3. Indicate the # p+, no, e- for each
A
B
C
Isotope Videos

Carbon Isotopes
Name the following mean elements
1.
2.
3.
4.
5.
6.
7.
8.
9.
Hg
Sn
Mn
Zn
As
Au
Pb
At
Sb
Find the symbol of the following
1.
2.
3.
4.
5.
6.
7.
8.
9.
Manganese
Zinc
Antimony
Mercury
Lead
Arsenic
Tin
Gold
Astatine
Find the AAM of
Element Terminium
83.25% 23.015 amu
6.78%
24.111 amu
9.97%
25.000 amu