Download Development of Atomic Theory

Welcome to PAP Chemistry!
 Tear
the exit ticket paper in half.
 How many protons, neutrons, and
electrons are in the following?
 Turn in to Ms. B
How will 2nd period succeed in
Unit 3?
 Pay
attention in class
 Turn in homework
 Study – PPTs (papchemistry.weebly.com),
videos online
How will 3rd period succeed in
Unit 3?
 Study
(look over notes, flashcards)
 Pay attention in class
 Tutoring
 Videos online (Bozenmann science, Crash
Course Chemistry, Khan Academy, Brain
Pop)
 Take notes
How will 4th period succeed in
Unit 3?
 Study
(reviewing notes, looking at
feedback)
 Take notes
 Do homework
 Tutoring
 Participation
How will 5th period succeed in
Unit 3?
 Pay
attention in class
 Take notes
 Do homework on time
 Turn in work
 Ask questions, go to tutoring
 Don’t interrupt class
 Papchemistry.weebly.com
How will 6th period succeed in
Unit 3?
 Take
notes
 Study (reviewing notes, watch crash
course chemistry, bozemann science
videos)
 Class discussions
 Turn in homework
Unit 3: Atomic Theory
 What
is atomic theory??
The idea that
matter is made
up of atoms,
the smallest
pieces of
matter.
Democritus
460-370 B.C.
 Proposed
world is
empty space
through which
atoms move
 Explained why
changes in matter
were possible 
the atoms were
being rearranged
Lavoisier
18th century
 Proposed
law of
conservation of mass/matter
 Observed
massreactants = massproducts
2.00 g of hydrogen + 16.00 g of oxygen
= 18.00 g of water
Proust
1871-1922
 Proposed
law of
definite proportions
for compounds
 Ex.
Water is always
11% hydrogen
and 89% oxygen
(by mass)
Atomic History Gallery Walk
 Time:
15 minutes
 Stations:
 Dalton
(father of atomic theory)
 J.J. Thomson
 Chadwick
 Rutherford
 Bohr
 Structure of the Atom
Scientist
Years
Theory
Democritus
460-370
B.C.
Proposed idea of atomos
n/a
Lavoisier
18th
century
Law of conservation of matter
n/a
18711922
Law of definite proportions
n/a
Dalton
17661844
Four postulates: 1) elements are made up of
atoms 2) elements are the same if they
have the same atoms 3) elements are
n/a
different if they have different atoms 4)
atoms form compounds in specific ratios
J.J.
Thomson*
Late
1800s
Plum pudding model, discovered electrons
Cathode
ray tube
Rutherford
18711937
Discovered that atoms are mainly empty
space and that mass is concentrated in a
positively charge nucleus
Gold foil
experiment
Chadwick
1932
Discovered the neutron
Various
Niels Bohr
Early
1900s
Bohr model with energy levels occupied by
electrons, energy is quantized
n/a
Proust
Experiment
Thomson’s Experiment
Voltage source
-
+
Thomson’s Experiment
Voltage source
+


By adding an electric field, he found that the moving pieces were negatively
charged
Able to calculate mass to charge ratio
Millikan’s Oil Drop Experiment
-
+
-
+
-Measure the drop and find volume from 4/3πr3
Find mass from M = D x V
-From the mass of the drop and the charge on
the plates, he calculated the charge on an electron
Rutherford Gold Foil Experiment
What he expected
Because he thought the mass was evenly distributed in
the atom
What he got
Model Over Time
Bohr’s Atom
•electron paths
Bohr Analogy
A
turtle sitting on a
ramp can have any
height above the
ground- and so, any
potential energy
A
turtle sitting on a
staircase can take on
only certain discrete
energies
energy is released when the turtle
moves down the steps (emission)
only discrete amounts of energy are
absorbed or released (energy is said to
be quantized)
Modern View
 Atom
is mostly empty space
 Two regions
 Nucleus contains protons and neutrons
 Electron cloud – region where you have a
chance of finding an electron
Atomic Structure:
Atoms contain three subatomic particles…
1. Protons…large, positive charge +1 These are
located in
2. Neutrons…large, no charge 0
NUCLEUS!
3. Electrons…*tiny, negative charge -1
Electrons surround the
nucleus in orbitals
Reading the Squares:
1st letter Capitalized
2nd letter Lowercase
Gold - Au
Iodine - I
Helium - He
ATOMIC
NUMBER
(number of protons)
ATOMIC
SYMBOL
6
C
12.011
Carbon
ATOMIC
MASS (mass
number = protons
plus neutrons)
What about neutrons?
 Nucleus
= mass of atom = protons + neutrons
 Proton mass = 1 amu
 Neutron mass = 1 amu
Boron – Atomic Number is 5.
Protons = 5
Mass = 11
Mass = Protons + Neutrons
How many Neutrons are in a Boron Atom? 6
Mass Number (NOT on the
Periodic Table)
 Mass
number = the sum of the protons and
neutrons
 Number of neutrons in an element can vary
(called isotopes: atoms of the same element
that have different mass numbers)
This means the number of
_protons_ is the same, and the
number of _neutrons_ is different.
How to write isotopes
2 methods
 Method
1: Hyphen-notation method
 The
symbol is written, then hyphen, then
mass #.
 U-235.
table)
Mass # = 235.
Atomic # = 92 (from periodic
Method 2: Subscript Superscript
Mass number →
Atomic number →
A
X
Z
23
Na
11
Isotopes of one element
Isotope Name
#P
#N
# e-
Mass #
Protium
1
0
1
1
Deuterium
1
1
1
2
Tritium
1
2
1
3
Notice the # Protons and # electrons is always the same
since these are all hydrogen.
Exit Ticket
 Answer
the following questions
using the picture to the right
1.
2.
3.
4.
5.
How many protons does carbon have?
How many electrons does carbon have?
What is the atomic mass of carbon?
What is the mass number of carbon shown
above?
How many neutrons does carbon have? Show
how you determined this.