Atomic Structure Chapter 4. Dalton’s Atomic Theory 4.1 John Dalton – 18 th century All matter is...
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Transcript of Atomic Structure Chapter 4. Dalton’s Atomic Theory 4.1 John Dalton – 18 th century All matter is...
![Page 1: Atomic Structure Chapter 4. Dalton’s Atomic Theory 4.1 John Dalton – 18 th century All matter is composed of atoms All atoms of a given element are identical.](https://reader036.fdocuments.net/reader036/viewer/2022062322/5697bfd11a28abf838caadc1/html5/thumbnails/1.jpg)
Atomic Structure
Chapter 4
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Dalton’s Atomic Theory 4.1
John Dalton – 18th century• All matter is composed of atoms• All atoms of a given element are identical• Atoms cannot be created, divided or
destroyed• Different atoms combine to form
compounds• In chemical reactions atoms are
rearranged.
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Subatomic Particles 4-2
Discovering the Electron-
• Thomson identified the electron
through use of a cathode ray tube.
• Electrons carry a negative charge
• Electrons have an extremely small mass
• Thomson created the plum pudding model (chocolate chip cookie dough model)
Electrons --- charge = -1 e-
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Plum Pudding Model
Negatively charged electrons were distributed throughout a uniform positive charge
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The Nuclear Atom 4.2
Rutherford’s Gold Foil Experiment
• Discovered the nucleus
• Atoms consist of mostly empty space through which the electrons move
• There is a tiny dense region (nucleus) which contains all of the atom’s positive charge and almost all its mass
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Gold Foil Experiment
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Plum Pudding Model
Nuclear Model
Because some of the alpha particles bounced back – they must have hit something with a positive charge
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What’s in the nucleus
Protons – subatomic particle with a charge equal and opposite to an electron
Proton --- charge = +1 p+
Neutrons – subatomic particle with a mass almost equal to that of a proton but it has no charge – neutral
Neutron --- charge = 0 n0
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How atoms differ 4.3
Atomic Number:
• The number of protons in an atom is the elements atomic number
• The number of protons in an atom identifies it as an atom of a particular element
• Atoms are neutral so # protons = # electrons
Example: Helium - He
Atomic # = 2 so it has 2 p+ and 2 e-
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How atoms differ 4.3
Isotopes and Mass Number
• Not all atoms of a particular element are identical. They all have the same atomic number (protons), but they can have a different number of neutrons
• Isotopes - same # of protons
different # of neutrons
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How atoms differ 4.3
Example:
• 3 types of potassium - all have 19 protons (that’s what makes them K)
- 20 neutrons; 21 neutrons; 22 neutrons
• Differ in mass, but they have the same chemical properties
Mass # = protons + neutrons
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How atoms differ 4.3
Example cont.
3 isotopes of Potassium
(same protons, different neutrons)
Potassium – 39 (19 + 20)
Potassium – 40 (19 + 21)
Potassium – 41 (19 + 22)
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Mass of Individual Atoms 4.3
Atomic Mass Units (AMU) Table 4-2
1 amu is almost equal to the mass of one
proton or one neutron
The atomic mass of an element is the average mass of the isotopes of that element
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Mass of Individual Atoms 4.3
Example: Chlorine - two isotopes
Chlorine – 35 and Chlorine – 37How many protons and neutrons does each have?
Isotopes Mass % abundance
Chlorine - 35 35.00 amu 75.0%
Chlorine - 37 37.00 amu 25.0%
Atomic Mass = 35.00 x 0.75 = 26.25
37.00 x 0.25 = 9.25
26.25 + 9.25 = 35.5 amu
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Mass of Individual Atoms 4.3
Practice Problem:
Isotopes Mass % abundance
Boron – 10 10.013 amu 19.8%
Boron – 11 11.009 amu 80.2%
10.013 x 0.198 = 1.982
11.009 x 0.802 = 8.829
1.982 + 8.829 = 10.811 amu
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Mass of Individual Atoms 4.3
Isotopes Mass % abundance
X – 6 6.015 amu 7.50 %
X - 7 7.016 amu 92.5 %
You Try:
6.015 x 0.0750 = 0.451 0.451
7.016 x 0.925 = 6.489 + 6.489 = 6.940 amu
What element has a average atomic mass of 6.94 amu?
Lithium (Li)
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Radioactive Decay 4.4
Nuclear Reactions – a rxn that involves a change in the atoms nucleus
• change in the # of protons
• atoms of one element turn into atoms of another element
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Radioactive Decay 4.4
Radioactivity – the process by which some substances spontaneously emit radiation
• They do this because they are unstable – they have a unstable ratio of protons to neutrons in their nucleus.
• They lose energy and undergo radioactive decay to become stable, non-radioactive atoms
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Radioactive Decay 4.43 types of radiation: Alpha, Beta, & Gamma
Alpha Radiation-
Alpha Particle - 2 p+ and 2 n0
- has a charge of 2+
- equivalent to a Helium -4 nucleus
- symbol = α or 42 He
Ex:
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Radioactive Decay 4.4
Beta Radiation-
Beta Particle – fast moving electrons
- negative charge ( -1)
- symbol = 0-1β
Ex:
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Radioactive Decay 4.4Gamma Radiation
Gamma Rays - 00γ
- high energy
- have no mass, no charge
- usually accompany alpha or beta
- don’t make a new atom by themselves
Ex:
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