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The Structure of the Atom The Building Block of Matter
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Atoms are the smallest particles of an element that retains the chemical properties of that element Parts: Nucleus – small region in the center of the atom. (+ charged protons, = charged neutrons) Electron Cloud – large region, compared to nucleus, where electrons are found.
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Size of nucleus vs. electron cloud If an atom was the size of a sports stadium, the nucleus would be the size of a marble! Subatomic Particles: Protons : + charge, relative mass = 1.007 atomic mass units (amu); round to 1 Neutrons: = charge, relative mass = 1.009 atomic mass units (amu); round to 1 Electrons: - charge, relative mass = 0.0005 atomic mass units (amu); round to 0 (not factored in when figuring total mass of an atom)
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Structure of Subatomic Particles Subatomic particles composed of fast moving points of energy called quarks Quark Calculations (for protons and neutrons) Each proton is 2 up quarks and 1 down quark 2(2/3) – 1(1/3) = 4/3 – 1/3 = 3/3 or +1 Each neutron is 2 down quarks and 1 up quark 2(-1/3) + 2/3 = 0 Each electron is composed of 2 down quarks 3(-1/3) = -1
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Atomic Number Number of protons in the nucleus (also the number of electrons) Typically the number on top of the symbol on the Periodic Table. 13 26.981 Atomic Number
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Mass Number Number of protons + number of neutrons in an atom. When solving for number of neutrons: round mass number properly, subtract atomic number from mass number.
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Element Symbols Hyphen Notation: Element symbol – Mass # (rounded) Example: Helium He-4 Nuclear Symbol: Superscript Mass Number, Subscript Atomic Number, Symbol Example: He 4 2
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IONS IONS are atoms or groups of atoms with a positive or negative charge. IONS are atoms or groups of atoms with a positive or negative charge. Taking away an electron from an atom gives a CATION with a positive charge Taking away an electron from an atom gives a CATION with a positive charge Adding an electron to an atom gives an ANION with a negative charge. Adding an electron to an atom gives an ANION with a negative charge. To tell the difference between an atom and an ion, look to see if there is a charge in the superscript! Examples: Na + Ca +2 I - O -2 To tell the difference between an atom and an ion, look to see if there is a charge in the superscript! Examples: Na + Ca +2 I - O -2 Na Ca I O Na Ca I O
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Forming Cations & Anions A CATION forms when an atom loses one or more electrons. An ANION forms when an atom gains one or more electrons Mg --> Mg 2+ + 2 e- F + e- --> F -
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Isotopes Atoms with the same number of protons & electrons but a different number of neutrons. They are the same element, but have different masses. (different mass number) All isotopes are used to calculate atomic mass (reason why weight is a decimal). Most elements consist of a mixture of isotopes.
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Average Atomic Mass Because of the existence of isotopes, the mass of a collection of atoms has an average value. Because of the existence of isotopes, the mass of a collection of atoms has an average value. Boron is 20% 10 B and 80% 11 B. That is, 11 B is 80 percent abundant on earth. Boron is 20% 10 B and 80% 11 B. That is, 11 B is 80 percent abundant on earth. For boron average atomic mass For boron average atomic mass = 0.20 (10 amu) + 0.80 (11 amu) = 10.8 amu = 0.20 (10 amu) + 0.80 (11 amu) = 10.8 amu 10 B 11 B
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How to determine Average Atomic Mass 1. Determine Relative Abundance – % abundance divided by 100 2. Determine weight of each isotope – multiply relative abundance by mass (keep all digits calculator gives you, no rounding yet) 3. Determine Average Atomic Mass - add up all individual weights, round to “2” decimal places
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How to determine Percent Abundance Use the following equation: Ave. Atomic Mass = (X)(Mass of 1 st isotope)+(1-X)(Mass of 2 nd isotope) 1. Solve for “X” 2. Answer will be a decimal 3. To solve for other isotope, do 1 – answer 4. Multiply both answers by 100 5. Two answer should equal 100
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Let’s see what you learned… Get your clickers ready!!!
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Which two subatomic particles are found in the nucleus of an atom? 1. Proton / Electron 2. Proton / Neutron 3. Electron / Neutron 4. Proton / Quark 5. Neutron / Quark 1234567891011121314151617181920 21222324252627282930
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The atomic number represents the number of … 1. Protons 2. Neutrons 3. Protons + Neutrons 4. Protons + Electrons 1234567891011121314151617181920 21222324252627282930
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The mass number represents the number of … 1. Electrons 2. Protons + Electrons 3. Protons + Neutrons 4. Neutrons + Electrons 1234567891011121314151617181920 21222324252627282930
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What is the correct Hyphen Notation for Calcium 1. Ca – 20 2. Ca – 40.078 3. Ca – 40.08 4. Ca – 40.1 5. Ca - 40 1234567891011121314151617181920 21222324252627282930
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An atom has 14 protons and 20 neutrons. The element is … 1. Si 2. Ca 3. Se 4. C 1234567891011121314151617181920 21222324252627282930
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An atom has 15 protons and 17 neutrons. What element is it? 1. Cl 2. He 3. Ge 4. P 1234567891011121314151617181920 21222324252627282930
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