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4.3 How Atoms Differ

4.3 How Atoms Differ. Atomic Number. - Atomic Number = # protons in an atom - # of protons determines kind of atom (atoms of an element always have the SAME number of protons) The atomic number = the number of electrons in a neutral atom

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4.3 How Atoms Differ

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  1. 4.3 How Atoms Differ

  2. Atomic Number - Atomic Number = # protons in an atom - # of protons determines kind of atom (atoms of an element always have the SAME number of protons) • The atomic number= the number of electrons in a neutral atom • Written just above the atomic symbol on the periodic table

  3. Complete the Table:

  4. Isotopes • All atoms in an element have the same number of protons • The number of neutrons vary • Atoms of an element with different numbers of neutrons = ISOTOPES

  5. http://www.youtube.com/watch?v=Jdtt3LsodAQ&feature=related Isotopes • Elements in nature = a mix of isotopes • The abundances of different isotopes are constant • EX: in ANY banana, 93% K has 20 neutrons, 7% have 22 neutrons

  6. Mass of atoms • One atomic mass unit(amu) is defined as 1/12th the mass of a carbon-12 atom. • One amu is nearly, but not exactly, equal to one proton or one neutron.

  7. Mass of subatomic particles

  8. Mass Number # PROTONS + # NEUTRONS = MASS NUMBER EXAMPLE: What is the mass number for manganese if there are 30 neutrons in the nucleus?

  9. Element Symbols • Top is mass number • Bottom is atomic number • Practice

  10. Symbols EXAMPLE 1: Find the • number of protons • number of neutrons • number of electrons • Atomic number • Mass Number 19 F 9

  11. Answer… • 9 protons • 10 neutrons • 9 electrons • Atomic # = 9 • Mass # = 19 • What would the mass number be of a fluorine isotope with two additional neutrons?

  12. Symbols EXAMPLE: Find the • number of protons • number of neutrons • number of electrons • Atomic number • Mass Number 80 Br 35

  13. Answer • Number of protons: 35 • Number of neutrons: 45 • Number of electrons: 35 • Atomic number: 35 • Mass Number: 80

  14. Symbols If an element has an atomic number of 34, a mass number of 78, find… • number of protons • number of neutrons • number of electrons • And WRITE the Complete symbol

  15. Answer… • 34 protons • 34 electrons • 44 neutrons • Symbol: Se 78 34

  16. Symbols If an element has 91 protons and 140 neutrons what is the……..? • Atomic number • Mass number • number of electrons • Complete symbol

  17. Pa 231 91

  18. Symbols If an element has 78 electrons and 117 neutrons what is the ………? • Atomic number • Mass number • number of protons • Complete symbol

  19. Pt 195 78

  20. Naming Isotopes • Put the mass number after the name of the element • carbon- 12 • carbon -14 • uranium-235

  21. Mass of the atom • Atomic mass on the periodic table is NOT an even # • The atomic mass of an element is the weighted average mass of the isotopes of that element • Depends on abundance of each isotope

  22. Atomic Mass How heavy is an atom of oxygen? The MASS NUMBERS we’ve been using are measured in amu 1 amu (atomic mass units) is ABOUT the mass of 1 proton or 1 neutron (or 1/12 of a carbon -12 atom) On the periodic table, the MASS of each element is NOT reported as a whole number… We can’t have HALF a proton or HALF a neutron in an atom… so why aren’t these masses whole numbers??

  23. Atomic Mass • Chlorine-35 is MORE common in nature than chlorine-37…so the mass of 1000 Cl atoms will be CLOSER to 35000 amu • To take the average of the two isotopes, we need to use the WEIGHTED AVERAGE: • In nature, 75.53% of Cl atoms are chlorine-35, and 24.47 % are chlorine- 37… • (% is called % abundance)

  24. Calculating the WEIGHTED AVERAGE • Write each percent as a decimal • Multiply that decimal by the isotope’s mass • Find the average by adding together Average = % as decimal x mass + % as decimal x mass • Average Mass of a Chlorine atom: (0.7553)(35) + (0.2447)(37) = 35.4894 amu % abundance isotope 2 % abundance isotope 1 Mass isotope 1 Mass isotope 2

  25. Atomic Mass: EXAMPLE - Calculate the atomic mass of copper if copper has two isotopes. 69.1% have a mass of 62.93 amu and the rest have a mass of 64.93 amu…

  26. ANSWER… Mass of Cu = (.691)(62.93) + (.309)(64.93) = 63.548 amu

  27. Atomic Mass: EXAMPLE 2 - Magnesium has three isotopes. 78.99% magnesium-24,10.00% magnesium-25, and the rest ismagnesium-26 amu. What is the atomic mass of magnesium?

  28. Answer… Mass of Magnesium = (.7899 x 24) + (.1000 x 25) + (.1101 x 26) = 24.3202 amu

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