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The Early Periodic Table First developed by Dmitri
Mendeleev Attempted to place elements
with similar properties near each other.
Organized according to combining capacity and atomic mass
Zumdahl, Steven S. Chemical Principles 5th Ed. Houghton Mifflin; 2005.
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Mendeleev’s Periodic Table
Zumdahl, Steven S. Chemical Principles 5th Ed. Houghton Mifflin; 2005.
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The Modern Periodic Table
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The Modern Periodic Table
Atomic Number increases as you go from left to right
Organized according to atomic number and electron arrangement (configuration)
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Electron Arrangement
Electrons are arranged in energy levels or shells around the nucleus of the atom
There are 7 energy levels Each shell holds a set number of electrons
1st Shell holds up to 2 electrons 2nd Shell holds up to 8 electrons 3rd Shell holds up to 18 electrons (8 for main
group elements) 4th Shell holds up to 32 electrons (8 for main
group elements)
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Electron Dot Diagrams
Shells are represented by circles and electrons are represented by dots.
2p
2n
Example: Helium
Nucleus: 2 protons, 2 neutrons
2 electrons in 1st shell
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More Examples
11p
12n6p
6n
Carbon
6 protons, 6 neutrons, 6 electrons
1st Shell: 2 electrons
2nd Shell: 4 electrons
Sodium
11 protons, 12 neutrons, 11 electrons
1st Shell: 2 electrons
2nd Shell: 8 electrons
3rd Shell: 1 electron
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Valence ElectronsThe electrons in the outermost electron shell.
2p
2n
6p
6n
11p
12n
Helium
2 Valence Electrons
Carbon
4 Valence Electrons
Sodium
1 Valence Electron
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Example
Draw electron dot diagrams and determine the number of valence electrons in the following elements:
Lithium Beryllium Sodium Magnesium
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Trends in Valence Electrons
Periodic table shows you how many valence electrons the Main Group Elements have Group 1A has 1 valence electron Group 2A has 2 valence electrons Group 3A has 3 valence electrons Etc.
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Periodic TableIA
IIAIIIA
IVA VA
VIA
VIIA
VIIIA
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Ions
Positively or negatively charged atoms Positively charged = cation Negatively charged = anion
Formed by gaining or losing electrons Why do atoms gain or lose electrons?
To achieve a stable electron configuration
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Octet Rule
Main Group elements will gain, lose, or share electrons to get eight valence electrons. 8 valence electrons = stable
configuration Metals lose electrons Non-metals gain electrons
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Example
11p
12n
Sodium Atom
1 Valence Electron
Charge = 11 + (-11) =0
11p
12n
Sodium Ion
8 Valence Electrons
Charge = 11 + (-10) = 1
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What happened?
A sodium atom lost an electron and became a sodium ion (Na+) Is it a cation or anion?
A Cation!
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Anion Example
9p
10n
Fluorine Atom
7 Valence Electrons
Charge = 9 + (-9) =0
9p
10n
Fluorine Ion
8 Valence Electrons
Charge = 9 + (-10) =-1
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Example
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Another Cation
12p
12n
12p
12n
Magnesium Atom
2 Valence Electrons
Charge = 12 + (-12) =0
Magnesium Ion
8 Valence Electrons
Charge = 12 + (-10) =2
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Another Anion
8p
8n
8p
8n
Oxygen Atom
6 Valence Electrons
Charge = 8 + (-8) =0
Oxygen Ion
8 Valence Electrons
Charge = 8 + (-10) =-2
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Average Atomic Mass
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C12.011
Atomic number
Average atomic mass (amu)
Why an average atomic mass?
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Isotopes
Isotopes are atoms of the same element that differ in the number of _________________. Same number of protons Same number of electrons Similar chemical behavior Different number of neutrons Different atomic mass Different isotopes are NOT equally
abundant (some are more rare)
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Isotope Notation
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What is the average atomic mass of carbon?
Isotope Atomic Mass % AbundanceCarbon-12 12 98.9
Carbon-13 13 1.1
Carbon-14 14 trace
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Picture Credits
Zumdahl, Steven S. Chemical Principles 5th Ed. Houghton Mifflin; 2005
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