the development of a modern theory of the atom aristotle democritus
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The Development of a Modern Theory of the Atom
Aristotle
Democritus
Ancient PhilosophyAristotle
When: More than 2000 years agoWhere: GreeceWhat: Aristotle believed in 4
elements: Earth, Air, Fire, and Water.
The Development of a Modern Theory of the Atom
Democritus (460-370 B.C)• Matter is composed of small, indivisible
particles called atomos.
Ancient Philosophy AND Politics Aristotle rejected Democritus’ ideas –
did not believe that empty space could exist
Aristotle more influential Ideas not science Aristotle’s ideas unchallenged for two
thousand years!!!
John Dalton
The Development of a Modern Theory of the Atom
Dalton (published 1803-1807)
1. All matter is composed of atoms, tiny, indivisible particles of an element that can not be created or destroyed.
Dalton’s Atomic Theory
The Development of a Modern Theory of the Atom
2. Atoms of one element can NOT be converted into atoms of another element. In reactions, atoms of the original substances recombine to form different substances.
Dalton’s Atomic Theory
The Development of a Modern Theory of the Atom
3. Atoms of an element are identical in mass and other properties and are different from atoms of any other element.
Dalton’s Atomic Theory
The Development of a Modern Theory of the Atom
4. Compounds result from chemical combination of a specific ratio of atoms of different elements.
Dalton’s Atomic Theory
The Development of a Modern Theory of the Atom
The Cathode Ray Tube
•Negatively charged particles are present in all matter (later named electrons)
•Cathode Ray Tube Animation
The Cathode Ray Tube
J. J. Thompson
The Development of a Modern Theory of the Atom
Thomson (published 1897)
charge to mass ratio
1.76 x 10-8 C/g
The electrons in an atom balance out the positive,
making it neutral
This can be compared to plums surrounding the
pudding in plum pudding
J.J. Thompson – 1897; England
Thompson credited with discovering electrons
Thompson knew atoms were neutral, but couldn’t find the positive particle.
The Development of a Modern Theory of the Atom
Millikan (published 1909) – “Oil Drop Experiment”
charge of electron = 1.60 x 10-19Cmass of electron = 9.10 x 10-28 g
• Millikan's Oil Drop Experiment
The Development of a Modern Theory of the Atom
Millikan•Oil Drop Experiment•Determined charge and mass of electron
The Development of a Modern Theory of the Atom
Rutherford (1871-1937)
The Development of a Modern Theory of the Atom
Rutherford (published 1910)
Rutherford’s Gold Foil Experiment
The Development of a Modern Theory of the Atom
Rutherford (published 1910)
1911- Rutherford’s Atomic Theory
1.Discovery of proton
2.Most of atom is empty space
3.There is a dense nucleus in the middle of every atom with protons surrounded by negative electrons which orbit around the nucleus.
James Chadwick
Discovered neutron!!!
ATOM BASICS
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Atomic Theory
Atoms are building blocks of elements
Similar atoms in each element
Different from atoms of other elements
Two or more different atoms bond in
simple ratios to form compounds
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Subatomic Particles
Particle Symbol Charge RelativeMass
Electron e- 1- 0
Proton p+ + 1
Neutron n 0 1
Atomic Structure
Atoms are composed of 2 regions:
NucleusElectron
Cloud
Atomic Structure
–Nucleus: the center of the atom that contains the mass of the atom
–Electron cloud: region that surrounds the nucleus that contains most of the space in the atom
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Atomic Number
Number of protons in an atom
All atoms of an element have the same number of protons
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Atomic Number -Periodic Table
11
Na
Atomic Number
Symbol
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Atomic Number -Periodic Table
11
Na
11 Protons
Sodium
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Learning Check
State the number of protons for atoms of each of the following:
Nitrogen
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Atomic Number -Periodic Table
7
N
7 Protons
Nitrogen
35
Learning Check
State the number of protons for atoms of each of the following:
Sulfur
36
Atomic Number -Periodic Table
16
S
16 Protons
Sulfur
37
Learning Check
State the number of protons for atoms of each of the following:
Barium
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Atomic Number -Periodic Table
56
Ba
56 Protons
Barium
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Mass Number
Counts the number of protons and neutrons in an atom
Mass number= p+ + n0
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Atomic Symbols
Show the mass number and
atomic number
Give the symbol of the
element
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Atomic Symbols
Na
Mass number
Atomic number
11
23
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Learning Check
Cl
Mass number
Atomic number
17
35 How many protons?
What is the element?
How many neutrons?
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Learning Check
Cl
Mass number
Atomic number
17
35
What is the element?
Chlorine
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Learning Check
Cl
Mass number
Atomic number
17
35 How many protons?
p = atomic # = 17
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Learning Check
Cl
Mass number
Atomic number
17
35How many neutrons?
n0 = 35 (mass number– 17 (p+)
n0 = 18
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Number of Electrons
An atom is neutral The net charge is zeroNumber of protons = Number of
electronsAtomic number = Number of
electrons
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Learning Check
O8
16 n0 =
p+ =
e- =
8
8
8
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Learning Check
P15
31 n0 =
p+ =
e- =
15
16
15
49
Learning Check
Zn30
65 n0 =
p+ =
e- =
30
35
30
50
IsotopesAtoms with the same number of
protons, but different numbers of
neutrons.
Atoms of the same element (same
atomic number) with different mass
numbers
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IsotopesIsotopes of chlorine
35Cl 37Cl17 17
chlorine - 35 chlorine - 37
LecturePLUS Timberlake 52
Learning Check
Naturally occurring carbon consists of three isotopes, 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of these carbon atoms.
12C 13C 14C 6 6 6
#p _______ _______ _______
#n _______ _______ _______
#e _______ _______ _______
LecturePLUS Timberlake 53
Solution
12C 13C 14C 6 6 6
#p 6 6 6
#n 6 7 8
#e 6 6 6
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Learning Check
An atom of zinc has a mass number of 65.
A. Number of protons in the zinc atom
B. Number of neutrons in the zinc atom
C. What is the mass number of a zinc isotope
with 37 neutrons? Draw its atomic symbol.
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Learning Check
An atom of zinc has a mass number of 65.
A. Number of protons in the zinc atom
30
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Learning Check
An atom of zinc has a mass number of 65.
B. Number of neutrons in the zinc atom
35
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Learning Check
C. What is the mass number of a zinc isotope
with 37 neutrons? Draw its atomic symbol.
67 Zn30
67
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Learning Check
Write the atomic symbols for atoms with the following:
A. 8 p+, 8 n, 8 e- ___________
B. 17p+, 20n, 17e- ___________
C. 47p+, 60 n, 47 e- ___________
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Solution
16OA. 8 p+, 8 n, 8 e- 8
B. 17p+, 20n, 17e- 37Cl 17
C. 47p+, 60 n, 47 e- 107Ag 47
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Atomic Mass on the Periodic Table
11
Na
22.99
Atomic Number
Symbol
Atomic Mass
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Atomic Mass Atomic mass is the weighted average mass of all the atomic masses of the isotopes of that atom.
BEAN BAGIUM
IONIon – charged particle that forms when an atom gains or loses one or more electrons
IONCation – positively charged particle when an atom loses electrons
protons(+) > electrons(-1)
CATION
Ca+2
protons(+) = 20
electrons(-) = 18
IONAnion – negatively charged particle when an atom gains electrons
electrons(-) > protons(+)
CATION
N-3
protons(+) = 7
electrons(-) = 10