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Warmup 9/24/14

Warmup 9/24/14. We have the ability to manipulate atoms and create molecules used for everything from medicine to warfare. Do you think there’s a point where we can “go too far” with this kind of thing? What kind of stuff would be wrong or immoral to create?. Objective Tonight’s Homework.

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Warmup 9/24/14

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  1. Warmup9/24/14 We have the ability to manipulate atoms and create molecules used for everything from medicine to warfare. Do you think there’s a point where we can “go too far” with this kind of thing? What kind of stuff would be wrong or immoral to create? Objective Tonight’s Homework To learn about atoms and groups of atoms with unbalanced charge p 103: 12, 13 p 105: 33, 34

  2. Ions and Isotopes We said that atoms connect and bond because they either give electrons or share electrons. But what happens if we have an atom sitting alone that’s somehow already gained or lost electrons?

  3. Ions and Isotopes We said that atoms connect and bond because they either give electrons or share electrons. But what happens if we have an atom sitting alone that’s somehow already gained or lost electrons? We call this an isotope.

  4. Ions and Isotopes We write isotopes like shown below. Be2+ In this example, we have a beryllium atom. It would normally have 2 valence electrons, but in this case, it has zero. “But 2 + 2 is 4, right?” You have to read this sort of backwards. The “2+” means that overall our atom now has a charge that is positive by 2. We can’t add protons to get that positive, so instead, we subtract electrons.

  5. Ions and Isotopes We can get the same thing in reverse as well. S2- Here we have a sulfur atom. They normally have 6 valence electrons, but this one has 2 extra, giving it 8. Once again, look at the “2-” as meaning “it has an overall charge of -2. We can’t change protons, so we have to add 2 electrons to get this -2.

  6. Ions and Isotopes We’ll see in a few days that we can also have whole groups of atoms that have an overall “not neutral” charge. NO3- This is nitrate. It’s a special molecule that doesn’t end up with the right number of electrons. If you draw the connections, you’ll see that NO3 ends up with 5 electrons in the middle. Why is this bad? We did say that a lot of atoms don’t follow the octet rule. And that’s true. But atoms really don’t want to have electrons in odd numbers. So in this case, this molecule finds another electron to have 6 around the middle.

  7. Ions and Isotopes We can also mess around with atoms by changing the number of neutrons in the center. This is where our notation gets a little more complex. Let’s look at carbon. C In the example above, the 6 represents the number of neutrons. This is the same as the element’s number on the periodic table. Awesome. The 12 represents the total of neutrons + protons. So to get neutrons, do the top number minus the bottom one. 12 6

  8. Ions and Isotopes Almost every element has natural isotopes. Versions that exist with less or more neutrons than there should be. For example, 1 out of every 100 carbon atoms is the one below. C C-14 is radioactive (but not much) and exists naturally. Most isotopes do. If you look at your periodic table, there’s a number below each element’s symbol. This number is an average of all the isotopes. For carbon, it reads 12.011. Just a little over 12 because of that 1-in-a-hundred C-14. 14

  9. Ions and Isotopes We also call our “proton + neutron” total the atom’s atomic mass. We measure how “heavy” atoms are with atomic mass units or (AMU). We can calculate an element’s AMU if we find the weighted average of all its isotopes. Let’s do an example:

  10. Ions and Isotopes Silicon has 3 common isotopes: Si-28 at 92.23% Si-29 at 4.67% Si-30 at 3.1% To get the average, we just multiply each amu by the decimal percentageand add. 28*.9223 + 29*.0467 + 30*.031 Average = 28.108 amu Simple as that!

  11. AMU Practice 1. The element copper has naturally occurring isotopes with mass numbers of 63 and 65.  The relative abundance and atomic masses are 69.2% and 30.8% respectively. Calculate the average atomic mass of copper. 2. Calculate the average atomic mass of sulfur if 95.00% of all sulfur isotopes are Sulfur-32, 0.76% are Sulfur-33 and 4.22% are Sulfur-34. 3. The four isotopes of lead are shown below, each with its percent by mass abundance and the composition of its nucleus. Using the following data, first calculate the approximate atomic mass of each isotope. Then calculate the average atomic mass of lead.   82p                            82p82p82p   122n                         124n                           125n                           126n   1.37%                     26.26%                       20.82%                     51.55% 4. Calculate the average atomic mass of bromine. One isotope of bromine has an atomic mass of 78.92amu and a relative abundance of 50.69%. The other major isotope of bromine has an atomic mass of 80.92amu and a relative abundance of 49.31%.

  12. Exit Question #16 What is an ion? a) When we add electrons to an element b) When we take away electrons from an element c) When we add neutrons to an element d) When we take away neutrons from an element e) There’s more than one correct answer f) None of the above

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