Gold foil experiment

1
Democritus
TheAtom
Dalton
There is an indestructible particle. atomos
There is an indestructible particle. atom
No experimental evidence
Supported by evidence.
Plato
e- discovered

• Law of conservation of matter.

Dismissed idea of the atom.

• Law of definite proportions.

Thomson (Plum Pudding Model)
Gold foil experiment

• Law of multiple proportions.

Bohr

• Places e- in orbits at fixed energy levels.

Rutherford

• Finds dense positive nucleus.

• Still contains a dense positive nucleus.

• Atom is mostly space with e- moving very far from
  the nucleus.

Modern Theory
e- are found based on probability.

• Still contains a dense positive nucleus.

2
Ch. 5 Atomic Theory
1. State the main ideas of Daltons atomic
theory.
3
The Atom

• The smallest unit of an element that retains the
  properties of that element.
• Building blocks for matter.

4
Size of the Atom

• Atoms are Tiny.

10 Copper atoms would be about a nanometer long.
Note 1 nanometer 1 billionth of a meter.
(1 cm of Cu 100 000 000 Cu atoms)

• Iron atoms on Copper atoms
• (Image using
• Scanning Tunneling Microscopy)?

• Highly
• Ordered
• Pyrolytic
• Graphite

5
Daltons Atom

• Atoms of the same element are the same.

Substance A From Minnesota
Substance A From Wisconsin

• Atoms of different elements are different.

Substance A
Substance B
6
Daltons Atom

• Atoms cant be divided, created or destroyed.

Dalton says Im Indestructible!
7
Daltons Atom

• Atoms of different elements combine in simple
  whole-number ratios to form compounds.

Atoms of A
?
Atom of B
Compound A2B
8
Summary for Daltons Atomic Theory

• Atoms are Tiny.
• Atoms of the same element are the same.
• Atoms of different elements are different.
• Atoms cant be divided, created or destroyed.
• Atoms of different elements combine in simple
  whole-number ratios to form compounds.

9
2. Characterize the size of an atom.
10
Size of the Atom

• Atoms are Tiny.

10 Copper atoms would be about a nanometer long.
Note 1 nanometer 1 billionth of a meter.
(1 cm of Cu 100 000 000 Cu atoms)

• Iron atoms on Copper atoms
• (Image using
• Scanning Tunneling Microscopy)?

• Highly
• Ordered
• Pyrolytic
• Graphite

11
2. Characterize the size of an atom.
Atoms are extremely tiny. Individual atoms
cannot be seen even with a microscope.
10 atoms would be about a nanometer (1
billionth of a meter).
Copper has about 100 000 000 atoms for every
centimeter.
12

• Democritus and Dalton both proposed that matter
  consists of atoms.
• How did their approaches to reaching that
  conclusion differ?

13
Early Greeks Two schools of thought
?Matter is made of indestructible particles
called atomos
Democritus (400 BC)
?Dismissed idea of the atom.
Both theories lacked Scientific Evidence so idea
of atom was lost for 2000 years
Plato (428-348 BC)
14
Daltons Theory

• Experimental evidence ? Scientific Laws
• Law of Conservation on Matter
• You cant create or destroy atoms.
• Law of Definite Proportions
• Same compounds are same ratio by mass.
• Law of Multiple Proportions
• Different compounds with the same elements are
  whole number multiples of the atoms.

• Experiments ? Scientific Laws ? Atomic Theory
• (observations) (Patterns) (Explanations)
• John Dalton realized that there must be an atom
  as Democritus first proposed.

15

• Democritus and Dalton both proposed that matter
  consists of atoms.
• How did their approaches to reaching that
  conclusion differ?

Democritus lacked the scientific evidence that
would have helped his argument. Scientific
testing was unknown during his time. His theory
also did not explain chemical behavior.
Dalton used scientific evidence to support his
theory. He found that when elements combined to
make compounds they always combined in simple
whole-number ratios according to their masses.
16
Ch. 5 Atomic Structure
Current Atomic model

• Dense nucleus contains the mass and positive
  charge.

• The electrons are far outside the nucleus. (e-
  cloud)

17
4. What are the charges and relative masses of
the three main subatomic particles?
Subatomic Particle Charge Mass (amu) Location
Proton, p
Neutron, n0
Electron, e-
18
Subatomic particle symbols
Subatomic Particle Symbol
Proton p
Neutron n0
Electron e-
19
4. What are the charges and relative masses of
the three main subatomic particles?
Subatomic Particle Charge Mass (amu) Location
Proton, p 1 1 Nucleus
Neutron, n0 0 1 Nucleus
Electron, e- -1 1 1840 Electron cloud (Very far outside the nucleus)
Note atomic mass unit (amu) 1 amu 1/12 the
mass of a carbon-12 isotope.
20
5. Describe the basic structure of the atom.
Atoms consist of a nucleus containing the protons
and neutrons.
Electrons are found in various locations at
relatively large distances away from the nucleus.
The nucleus is difficult to get at because it is
surrounded by the outer electrons so when
elements react with other elements it usually
results in changes to the electrons only.
21
The Atomic Scale

• Most of the mass of the atom is in the nucleus
  (protons and neutrons)
• Electrons are found outside of the nucleus
• (the electron cloud)
• Most of the volume of the atom is empty space

q is a particle called a quark
22
About Quarks(particles that make up protons and
neutrons)
Protons and neutrons are NOT fundamental
particles.
Protons are made of two up quarks and one
down quark.
Neutrons are made of one up quark and two
down quarks.
Quarks are held together by gluons
23
Electrical Nature of Matter

• Opposite charges attract each other.
• () (-)
• Like charges repel each other.
• () ()
• (-) (-)

24
Discovery of the Electron
In 1897, J.J. Thomson used a cathode ray tube to
deduce the presence of a negatively charged
particle he called the electron.
Crookes Tube
Cathode ray tubes pass electricity through a gas
that is contained at a very low pressure.
25
Thomsons Atomic Model (1897)
Thomson believed that the electrons were like
plums embedded in a positively charged pudding,
thus it was called the plum pudding model.
26
J.J. Thomson (1897)
Discovered the electron by working with the
cathode ray tube (Crookes tube).
Cathode rays were deflected by a negative field
so they were negatively charged particle.
Thomson revised Daltons model by showing equal
amounts of positive and negative charged
particles.
Thomson named his model of the atom the Plum
Pudding Model after a common dessert.
27
Mass of the Electron
1909 Robert Millikan determines the mass of the
electron.
The oil drop apparatus
Mass of the electron is 9.109 x 10-31 kg
Thats about 2000 times smaller than a proton!
28
Millikans Oil Drop Experiment (1909)

• Compared different masses and charges on an oil
  drop.
• Used electric field to determine charge.
• Used gravity to determine mass.

29
Robert A. Millikan (1868-1953)
Carried out experiments (Oil drop experiment)
that allowed him to find the quantity of charge
carried by an electron.
From the oil-drop experiment he was able to
determine the relative charge to mass ratio of an
electron..
Millikan determined the mass of an electron was
2000 times smaller than the mass of a single
hydrogen atom.
Mass of the electron is 9.109 x 10-31 kg Thats
really small.
30
RutherfordsGold Foil Experiment
()
Radioactive source

• Alpha particles are helium nuclei, He2
• Particles were fired at a thin sheet of gold
  foil
• Particle hits on the detecting screen (film) are
  recorded

31
Rutherfords Findings (1911)

• Observations
• Most of the alpha particles passed right through
• Some alpha particles were deflected slightly
• VERY FEW were greatly deflected

Like howitzer shells bouncing off of tissue
paper!
Conclusions

• The atom is mostly empty space.
• The nucleus is dense.
• The nucleus is positively charged
• Electrons, e-, are moving large distances
  outside the nucleus.

32
Rutherfords Conclusion (1911)

• Small, dense, positive nucleus.
• Equal amounts of (-) electrons at large distances
  outside the nucleus.

33
The conclusions Evidence to support conclusion
The atom is mostly empty space. (Most ? particles went straight through)
The mass of the atom is located in a dense central core called the nucleus. (A few ? particles bounced back)
The nucleus has all the positive charge. The ? particles deflected or bounced back. Like charges repel each other. The () alpha particles were repelled by the nucleus.
Electrons must be in motion around the nucleus since they do not crash into the nucleus (Most ? particles went straight through)
34
Democritus
TheAtom
Dalton
There is an indestructible particle. atomos
There is an indestructible particle. atom
No experimental evidence
Supported by evidence.
Plato
e- discovered

• Law of conservation of matter.

Dismissed idea of the atom.

• Law of definite proportions.

Thomson (Plum Pudding Model)
Gold foil experiment

• Law of multiple proportions.

Bohr

• Places e- in orbits at fixed energy levels.

Rutherford

• Finds dense positive nucleus.

• Still contains a dense positive nucleus.

• Atom is mostly space with e- moving very far from
  the nucleus.

Modern Theory
e- are found based on probability.

• Still contains a dense positive nucleus.

35
Isotope symbols
Hydrogen-1 (Protium)
Chemical Symbol (Hydrogen)
Mass (p n0)
1
H
1 proton 0 neutrons 1
Atomic (p)
1
36
Isotope symbols
Hydrogen-1 (Protium)
Hydrogen-2 (Deuterium)
Hydrogen-3 (Tritium)
3
1
2
H
H
H
1
1
1
1 proton 2 neutrons 3
1 proton 0 neutrons 1
1 proton 1 neutrons 2
Isotopes only differ by number of neutrons.
37
Calculating Average Mass
Atomic mass is the average of all the naturally
isotopes of that element.
Copper 63.546 amu
Example
Copper-63 69.2 with 62.93 amu Copper-65
30.8 with 64.93 amu
x
62.93 amu
0.692
43.54756 amu
Copper-63

Copper-65
x
64.93 amu
0.308
19.99844 amu
63.546 amu
69.2 100
0.692
30.8 100
0.308
Atomic mass (average)
38
Atomic Particles
Subatomic Particle Symbol Charge Location Relative Mass (amu)
Proton p
Electron 1-
Neutron Nucleus 1 amu
1
Nucleus
1
1
Very far outside nucleus
e-
1840
n0
0
Note atomic mass unit (amu) 1 amu 1/12 the
mass of a carbon-12 isotope.
39
Your Turn
Isotope Symbol Atomic neutrons electrons Mass Number (p n0) Isotope Mass in (amu) Relative abundance
Carbon-12 6C 6 12 - 6 6 6 - 6 6 12 12.000 98.89
Carbon-13 6C 6 13 6 7 6 - 6 7 13 13.003 1.11
Nitrogen-14 N 14.003 99.63
Nitrogen-15 N 15.000 0.37
Chlorine-35 Cl 34.969 75.77
Chlorine-37 Cl 36.966 24.23
12
13
14
7
7-
14
14-77
7
15
7
7-
15
15-78
7
35
17
17-
35
35-1718
17
37
17
17-
37
37-1720
17
Atomic mass (average)
40
Your Turn (Calculate Average Mass)
Isotope Symbol Atomic neutrons electrons Mass Number (p n0) Isotope Mass in (amu) Relative abundance
Carbon-12 6C 6 12 - 6 6 6 - 6 6 12 12.000 98.89
Carbon-13 6C 6 13 6 7 6 - 6 7 13 13.003 1.11
12
13
x
12.000 amu
0.9889
11.8668 amu
Carbon-12

Carbon-13
x
13.003 amu
0.0111
0.1443333 amu
12.0111333 amu
12.01 amu
Atomic mass (average)
41
Your Turn (Calculate Average Mass)
Isotope Symbol Atomic neutrons electrons Mass Number (p n0) Isotope Mass in (amu) Relative abundance
Nitrogen-14 N 14.003 99.63
Nitrogen-15 N 15.000 0.37
Chlorine-35 Cl 34.969 75.77
Chlorine-37 Cl 36.966 24.23
14
7
7-
14
14-77
7
15
7
7-
15
15-78
7
35
17
17-
35
35-1718
17
37
17
17-
37
37-1720
17
x
14.003 amu
0.9963
13.9511889 amu
Nitrogen-14

0.0555 amu
Nitrogen-15
x
15.000 amu
0.0037
14.0066889 amu
14.007 amu
42
Your Turn (Calculate Average Mass)
Isotope Symbol Atomic neutrons electrons Mass Number (p n0) Isotope Mass in (amu) Relative abundance
Nitrogen-14 N 14.003 99.63
Nitrogen-15 N 15.000 0.37
Chlorine-35 Cl 34.969 75.77
Chlorine-37 Cl 36.966 24.23
14
7
7-
14
14-77
7
15
7
7-
15
15-78
7
35
17
17-
35
35-1718
17
37
17
17-
37
37-1720
17
x
34.969 amu
0.7577
26.4960113 amu
Chlorine-35

8.9568618 amu
Chlorine-37
x
36.966 amu
0.2423
35.4528731 amu
35.453 amu