1. 0:56
0:55
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0:44
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1:03
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1:19
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1:25
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1:15
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1:08
1:07
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1:09
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1:11
0:40
0:39
0:09
0:08
0:07
0:06
0:10
0:11
0:15
0:14
0:13
0:12
0:05
0:04
0:00
0:00
0:00
0:00
0:00
0:00
0:03
0:02
0:01
0:00
0:16
0:17
0:32
0:31
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0:33
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0:28
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0:21
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3:00
1:26
2:30
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2:36
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2:26
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2:37
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2:53
2:52
2:51
2:50
2:54
2:55
2:59
2:58
2:57
2:56
2:49
2:48
2:42
2:41
2:40
2:39
2:43
2:44
2:47
2:46
2:45
1:27
2:14
1:43
1:42
1:41
1:40
1:44
1:45
1:49
1:48
1:47
1:46
1:39
1:38
1:31
1:30
1:29
1:28
1:32
1:33
1:37
1:36
1:35
1:34
2:13
1:50
2:06
2:05
2:04
2:03
2:07
2:08
2:12
2:11
2:10
2:09
1:51
2:02
1:55
1:54
1:53
1:52
2:01
1:56
2:00
1:57
1:59
1:58
Do Now
Do not copy this question, just answer it

2. The Discovery of Neutrons
Isotopes
The Discovery of Neutrons

3. Subatomic Particles Particles found inside the atom Electrons
The number of electrons vary for atoms of a single element. The # of electrons = the # of protons in a neutral atom
Negative
Revolve around the nucleus
Mass = 1/1836amu or 0 because it is so small

4. Subatomic Particles Protons
The # of protons determines what element the atom is. Every H has 1p, C has 6, He has 2….
Positive
Found in the nucleus
Mass = 1amu

5. Subatomic Particles Neutrons
The number of neutrons vary for atoms of a single element. H can have 0, 1, or even 2 neutrons.
Neutral
Found inside the Nucleus
Purpose is to hold repelling protons together
Mass = 1amu

6. Summary of Subatomic Particles
Location
Mass
Relative Mass
Charge
Proton
Electron
Neutron
Nucleus
1.67 × 10−27 kg
1 amu +1
Outside
9.11 × 10−31 kg
0 amu −1
Nucleus
1.67 × 10−27 kg
1 amu

7. Oops! Dalton Goofed! mass.
Dalton’s discovery of atoms depended on one major characteristic of atoms . . .
One of Dalton’s postulates says the following about mass:
But in 1911 while trying to study the atomic nucleus, J. J. Thomson accidently discovered that neon could have two different atomic masses.
He called them…
mass.
Atoms of an element are identical. They have the same mass.

8. Isotopes The electrons and protons.
Atoms of the same element with different atomic masses.
Atoms of the same element have the same properties.
But what causes the chemical properties of an atom?
So atoms of different isotopes of an element must have the same number of protons and electrons.
Whatever causes isotopes to have different masses must be an electrically neutral particle.
The electrons and protons.

9. The Discovery of Neutrons
In 1930, scientists showed that bombardment of beryllium with alpha particles produced neutral radiation.
Measurements by Sir James Chadwick in 1932 proved that this neutral radiation was a particle with a mass similar to a proton.
This neutral particle is called a neutron.
James Chadwick

10. x A Z Isotopic Notation Element symbol (X) Atomic number (Z)
# of protons
Mass number or Atomic mass (A)
# of protons + # of neutrons
Example: x A Z

11. Naming Isotopes Put the mass number after the name of the element. 12C
Carbon-12 or C-12
14C
Carbon-14 or C-14
235U
Uranium-235 or U-235

12. Na Practice 24 11 Find the number of protons number of neutrons
number of electrons
Atomic number
Mass Number
Name 24 Na 11

13. Br Practice 80 35 Find the number of protons number of neutrons
number of electrons
Atomic number
Mass Number
Name 80 Br 35

14. Practice
An element has an atomic number of 34 and a mass number of 78 what is the
number of protons
number of neutrons
number of electrons
Complete symbol
Name

15. Practice An element has 91 protons and 140 neutrons what is the
Atomic number
Mass number
number of electrons
Complete symbol
Name

16. Practice An element has 78 electrons and 117 neutrons what is the
Atomic number
Mass number
number of protons
Complete symbol
Name