outline the history of the atomic model
DESCRIPTION
Outline the history of the atomic model. Agenda for Tuesday Dec 14 th Atoms Atomic mass, #, protons, etc. Atoms. Nucleus in the center Protons and neutrons Electrons on outside of nucleus Electron cloud model Electrons exist in energy levels – based on # of electrons. - PowerPoint PPT PresentationTRANSCRIPT
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Outline the history of the atomic model.
Agenda for Tuesday Dec 14th 1. Atoms2. Atomic mass, #, protons, etc
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Atoms
• Nucleus in the center– Protons and neutrons
• Electrons on outside of nucleus– Electron cloud model– Electrons exist in energy levels – based on # of
electrons
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Atomic Number and Atomic Mass
Bboron
5
10.811
Element nameAtomic number
Symbol
Atomic mass
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• Atomic number: # of protons in nucleus
• Each element has a different atomic #
• Identifies the element
• Hydrogen = smallest atomic # (1)
• # of protons = # of electrons
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• Atomic mass: total mass of protons and neutrons in an atom, measured in atomic mass units (amu)– Atomic weight
• Atoms of the same element can have different numbers of neutrons - isotopes
• # on periodic table is the average atomic mass for that element
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• We will round the average atomic mass to get a whole # called the mass number.
• Examples:Sodium (Na)
Avg. atomic mass = 22.990 amuMass # = 23
Nitrogen (N)Avg. atomic mass = 14.007 amuMass # = 14
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• Finding # of neutrons
mass # - atomic # = # of neutrons
For Na: 23 – 11 = 12 neutrons
For N:14 – 7 = 7 neutrons
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Practice
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Find the mass number, protons, neutrons, and electrons for Bromine.
Agenda for Wednesday Dec 15th 1. History of the Atom Flash Cards2. Practice with mass, protons, etc3. Isotopes
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ElementName
AtomicNumber
Number ofProtons
Number ofNeutrons Mass Number
carbon 12
8 8
hydrogen 1
6 14
hydrogen 2
nitrogen 14
6 66
7 7 7
1 1 3
86
1 01
168Oxygen
Carbon
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Isotopes• Atoms of the same element can have different numbers of
neutrons isotopes
• # of protons and electrons stays the same for a particular element– Mass changes– Means # of neutrons changes
• Atomic mass on your P.T. is an average of all the isotopes
• For Boron:.8 (10 amu) + .2 (11 amu) = 10.811 amu
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More on Isotopes
• Because the numbers of neutrons in the isotopes are different, the mass numbers are also different
• You use the name of the element followed by the mass number of the isotope to identify each isotope: boron-10 and boron-11
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• Example: – Neon. All neon atoms have 10 protons and 10
electrons. Some neon atoms have 10 neutrons and some have 12.
– Both isotopes of neon
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Ne or Ne-20
Ne or Ne-22
10
10
20
22
Atomic # (# of protons)
Atomic # (# of protons)
Mass # (protons + neutrons). Different for each isotope
Mass # (protons + neutrons). Different for each isotope
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What’s the point of Isotopes
• You can tell how old something is– Radiocarbon Dating
• Use as markers in research– Follow a certain molecule, atom
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Practice ProblemsYou will need your periodic table!
1. For Mg-25: How many protons, electrons, and neutrons?
2. For N-15: How many protons, electrons, neutrons?
3. For P-31: How many protons, electrons, neutrons?
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Practice
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What is an isotope?
Agenda for Thursday Dec 16th 1. Mass #, Atomic weight, proton review2. Valence Electrons3. Lewis Dot Structures
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Atoms
• Nucleus in the center– Protons and neutrons
• Electrons on outside of nucleus– Electron cloud model– Electrons exist in energy levels – based on # of
electrons
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Valence Electrons
• Electrons in the outermost energy level
• Valence electrons determine reactivity and other chemical properties
• 8 valence electrons means a stable atom = do not want to react with other atoms
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Where are electrons found?NucleusLeast likely
Most likely
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13 p+
14 n0
Help! We’re so
vulnerable!
Valence electrons
•A way to draw an atom showing where electrons are found
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Valence electrons
Carbon -12 has 4 electrons in the last energy level . . .
therefore carbon-12 has 4 valence electrons
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Bohr’s Model
Nucleus
1st shell can hold 2 e-
3rd shell can hold 8 e-
2nd shell can hold 8 e-
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How many electrons in each shell?
• 1st shell = 2 electrons• 2nd shell = 8 electrons• 3rd shell = 8 electrons• 4th shell = 18 electrons
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Drawing Carbon-12 with Bohr’s ModelSteps:1. Find number
of neutrons and protons.
2. Find number of electrons.
3. Fill in electrons, beginning with the 1st energy level.
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How many valence electrons does Nitrogen have?
NUCLEUS
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How many valence electrons does Calcium have?
Calcium has 2 Valence electrons
NUCLEUS
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How many valence electrons does Phosphorous have?
Phosphorous has 5 Valence electrons
NUCLEUS
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How many valence electrons does Boron have?
NUCLEUS
Boron has 3 Valence electrons
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Cool Trick!
162 3 4 5 7
8