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The Atom

The Atom. Isotopes. Drill. You completed problem #2 on the Structure of the Atom WS yesterday. Pull out that worksheet. We will go over #2. Objectives. iWBAT determine the number of protons, neutrons and electrons for isotopes

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The Atom

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  1. The Atom Isotopes

  2. Drill • You completed problem #2 on the Structure of the Atom WS yesterday. • Pull out that worksheet. • We will go over #2.

  3. Objectives • iWBAT • determine the number of protons, neutrons and electrons for isotopes • Explain how isotopes are different from neutral atoms and ions.

  4. Guided Notes • Pick up a copy of the “Isotopes” Guided Notes WS

  5. Isotopes are like twins

  6. ISOTOPES • atoms that have the same number of protons, but different numbers of neutrons • the chemical properties of an element depend primarily on its electrons and protons • isotopes of the same element, with different numbers of neutrons have essentially the same chemical properties

  7. ISOTOPES the major difference between 2 isotopes is their mass • isotopes with more neutrons have higher mass than those with fewer neutrons • mass # = (isotope’s # of p+) + (isotope’s # of n0) • to identify an isotope you add the mass number after the element’s name (i.e. chlorine -37) • number of neutrons = mass # - atomic #

  8. On Your Notes • Chlorine is used as an example. • We will look at two chlorine isotopes • Chlorine – 35 • Chlorine - 37 • The “35” and “37” represent mass numbers. • Do you remember how to determine a mass number?

  9. Determine the # of neutrons for each isotope of chlorine • Chlorine – 35 has 18 neutrons • Chlorine – 37 has 20 neutrons • Both isotopes have the same number of protons and electrons, but different numbers of neutrons.

  10. Carbon-12 • The entire periodic table is based on the carbon-12 isotope. • You can write the isotope as: carbon-12 (the line is a dash not minus sign) or 12 C (notice how the mass # is written at the top of the symbol)

  11. Example Protons don’t change Mass number p+ e- nº Carbon-12 6 6 6 Carbon-14 6 6 8 2 extra neutrons Electrons don’t change

  12. Iodine-125 • What is the difference between this isotope of iodine and the iodine shown on the periodic table? • How many neutrons does iodine-125 have?

  13. Practice • Pick up a copy of the “Structure of the Atom” WS • Answer question “5” only

  14. Average Atomic Mass • Take a look at the Periodic Table. • Notice that the atomic mass for most of the elements is not a whole number. • This is because there are various isotopes for each element. • The average atomic mass of the element is calculated and that is what you see as the mass on the periodic table.

  15. Avg Atomic Mass • Pick up a copy of the Isotopes and Average Atomic Mass WS. • Let’s look at the example in the box at the top of the page.

  16. Example • A sample of cesium is 75% 133 Cs, 20% 132 Cs and 5% 134 Cs. What is its average atomic mass? • Change the % into a decimal. • Multiply the decimal times the mass #. • Add all of the answers. 0.75 x 133 = 99.75 0.20 x 132 = 26.4 0.05 x 134 = 6.7 132.85 amu You will sometimessee the mass withunits of amu “atomic mass units”

  17. Your Grade • We use a math process like Average Atomic Mass to calculate your grade. • 50% assessments • 30% labs • 20% home/classwork

  18. Your Grade • If you currently have… 89.4 % for assessments 73.7 % for labs 84.1 % for home/classwork What is your overall grade for the marking period?

  19. Your Grade • Assessments 50% becomes 0.50 • Labs 30% becomes 0.30 • home/classwork 20% becomes 0.20 Assessments 89.4 % x 0.50 = 44.7 Labs 73.7 % x 0.30 = 22.11 home/classwork 84.1 % x 0.20 = 16.82 83.63

  20. Summary • Explain the difference between a neutral atom, ion and isotope.

  21. Summary Protons: An atom’s identity is determined by the number of protons. If you change the number of protons, you change the element. Neutrons: Neutrons maintain stability. If you change the number of neutrons, you have an ISOTOPE. Electrons: Electrons determine an atom’s behavior. If you change the number of electrons, then you have an ION.

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