MATTER : matter can be classified into mixtures, solutions, elements and compounds.
Chapter 4 Atomic Theory Matter Matter All matter is made of atoms o Alone as elements Au, Na, O, He...
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Transcript of Chapter 4 Atomic Theory Matter Matter All matter is made of atoms o Alone as elements Au, Na, O, He...
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Chapter 4Atomic Theory
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Matter
• All matter is made of atoms
o Alone as elements• Au, Na, O, He
o In combination of elements as compounds
• H2O, NaCl, LiO2
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• Democritus (460-370 B.C.) proposed & believed thato Matter was not infinitely
divisibleo Made up of tiny particles
called atomos or “indivisible”
o Atoms could not be created, destroyed, or further divided
o He did not do any experiments that backed up his theory.
Early Theories of Matter
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John Dalton, 19th Century
• School teacher
• Dalton revised Democritus's ideas based upon the results of scientific research he conducted
• Dalton’s atomic theoryo Not totally correct
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Dalton’s First Atomic Theory:
o Elements are made up of small indivisible particles called atoms
o Atoms of the same element are identical, different elements are different- (Same size, mass and chemical properties)
o Atoms are not created or destroyed in a chemical reaction
o A compound always has the same relative numbers and kinds of atoms
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What is an atom?• An atom is the smallest particle of an element
that retains the properties of the element
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Atomic Models
• Thomson: Plum Pudding Model
• Based off experiments using cathode rays
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Atomic Models• Based off of his Gold
foil experiments• Rutherford:
Electron Cloud Model
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Rutherford: The Nuclear Atom
• His model consisted of the following ideas:
o an atom consists mostly of empty space through which electrons move
o electrons are held within the atom by their attraction to the positively charged nucleus
o small, dense, positive charged nucleus
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Bohr Model
• Based on Rutherford’s model
• “Planetary” model
• Adds idea of “quantized” energy levels
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Quantum Model• Schrodinger (1920’s) came up with the modern
atomic model: proposing that electrons travelled in wave-like patterns
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Inside an atom: subatomic particles
• These particles have mass and charge
• Nucleus holds protons & neutronso Protons: + chargeo Neutrons: Ø charge
• Outside of nucleus is the electron cloudo Electron: - charge
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Parts of the AtomName Symbol Charge Mass Location
proton p +1 1 amu nucleus
neutron n 0 1 amu nucleus
electron e- -1 ~ 0 amu outside nucleus
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Atomic Mass Unit (amu)
• Small mass #’s are not easy to work with, so the atomic mass unit (amu) was developed
• The mass of 1 amu is nearly equal to the mass of one proton or neutron
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Reading the Periodic Table
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Atomic Number• The number of protons determine the
element (ALWAYS!!!)
• Number of protons are unique to each element
• Examples:o Carbon (C) has 6 protons
• Atomic number is 6
o Copper has 29 protons• Atomic number is 29
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Atomic Number
• In uncharged atoms, atomic number is also the number of electronsoWhy? o If an atom is charged, then it is an ion
• Uncharged atom:
Atomic number = # of protons = # of electrons
Charge = # protons - # electrons
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Mass Number
• To find the Mass number # protons + # neutrons = mass number
• To find # neutrons mass number – proton (or atomic number) =
neutrons
• Mass numbers are always WHOLE #’s!!
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Symbols for Atoms
X= symbol of elementA= mass numberZ= number of protons
X or X
- Can also be written “element - A”- i.e. carbon - 12
AZ
A
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Mg-25 Zn
atomic #
proton
neutron
electron
mass #
12
12
13
12
25
30
30
40
30
70
7030
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Turn to your partner and summarize…
• How does the number of protons affect the identity of the atom?
• How do the number of protons and electrons relate to each other in a neutral atom?
• What is an ion?
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Isotopes and Mass Number
C C carbon-12 carbon-13
Isotopes are atoms with the same number of protons but different number of neutrons
13
6126
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Isotopes and Mass Number
• Example: 3 types of Potassium
All 3 types contain 19 protons and __ electrons
# of Protons # of Neutrons Mass Number
19 20 19 21 19 22
19
39
40
41
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What’s the difference between mass
number and average atomic
mass(weight)?
C carbon-12
But if you look on the periodic table, the number states 12.01…
Atomic Mass (atomic weight) – a weighted average of the masses of all of the isotopes of that element. It is not the same as the mass number.
12 6
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What’s the difference between mass
number and average atomic mass?
• Mass number- specifically about one isotope; the number of protons + neutrons
• Average atomic mass- includes the masses of all the different isotopes for that element
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Mass of Individual Atoms
• Average atomic mass:o The weighted average mass of the isotopes of
an element
o Example: Chlorine• Mixture of 75% chlorine-35 and 25%
chlorine-37
Atomic mass = (0.75)*35.0 + (0.25)*37.0 = 35.5 amu
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Try this one• 3 isotopes of neon:
o Ne-20 (90.92%)o Ne-21 (0.25%)o Ne-22 (8.83%)
What is the average atomic mass of Ne?
(20)*(0.9092) + (21)*(0.0025) + (22)*(0.0883) =
20.18 amu
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Radioactivity – when the nucleus of an atom is unstable causing it to decompose into another nucleus
There are three types of radioactive decay:
1.Alpha Decay
2.Beta Decay
3.Gamma Decay
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Shielding: Alphas, Betas, Gammas and Neutrons
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Alpha Decay• An alpha particle (α ) is produced • An alpha particle is just a helium nucleus,
He+242
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Beta Decay• An e- is kicked out of the nucleus (a neutron
breaks up into a proton and e-), e 0-1
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Gamma Decay• Only ENERGY is released from the nucleus• the nucleus itself does not change, but almost
always accompanies alpha and beta decay
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•Alpha Decay230
90Th 42He + 226
88Ra
22288Ra
•Beta Decay234
90Th 0-1e + 234
91Pa
13153I
•Gamma Decay238
92U 42He + 234
90Th + energy
42He + 218
86Rn
0-1e + 131
54Xe
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What are the products of Po-218 after it undergoes alpha decay followed by a beta decay, followed by beta decay followed by alpha decay?
21884Po 4
2He + 21482Pb
21482Pb 0
-1e + 21483Bi
21483Bi 0
-1e + 21484Po
21484Po 4
2He + 21082Pb
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Where Does the Radiation Come From?• The radiation you receive can be either Natural or Man-
made
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Turn to your partner and summarize…
• List the 3 types of radioactive decay and the particle that is released in each
• Which type of radioactive decay is most penetrating?
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Half-Life (t1/2) - time required for one half of the original sample of nuclei to decay.
•The half-life of Ra-223 is 12 days. If you start with 100.0 grams of Ra-223, how much will be left after 36 days?
100.0 g 50.00 g 25.00 g 12.50 g
•The half life of Ra-225 is 15 minutes. If you have 10.0 grams now, how much did you start with 60 minutes ago?
•10.0 g 20.0 g 40.0 g 80.0 g 160.g
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Fission – splitting a nucleus into two or more smaller nuclei
1 n + U Kr + Ba + 3 n + energy
• This is what takes place in a nuclear reactor or an atomic bomb.
235 92
9236
141 56
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F ission• chain reaction - self-propagating reaction
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Fusion – combining of two nuclei to form one nucleus of larger mass
H + H He + 1n + energy
• This is how all of the elements were created in nature and occurs naturally in stars.
21
31
42
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