Mission 1: Itty Bitty Things.
Mission Objectives: You should be able to...
1. Describe the structure of an atom.
2. Describe the structure of an isotope.
3. Explain the difference between atomic number and mass number.
4. Calculate the average atomic mass of an element.
All neutral atoms contain the same number of protons & electrons. The number of protons determines the element's identity. For instance, 8 protons = oxygen. 17 protons = chlorine. 20 protons = calcium. This does not change.
Electrons determine chemical behavior. Valence electrons (electrons in the outermost energy levels) are significant in this regard, because the number of valence electrons determine how an element behaves in certain conditions. Elements with an octet (8 valence electrons) are unusually stable and do not combine to form compounds (noble gases have an octet, with the exception of helium).
Neutrons determine isotopes. They do not affect the charge or the element's identity. However, they do affect the mass of the nucleus. Several elements have multiple isotopes. Almost every element has isotopes, and what is represented on the periodic table is an average of all of the isotopes of a particular element (which is why the atomic mass is a decimal). In a later mission, you will learn how to use mass spectrum data to calculate relative atomic mass (RAM).
This is basic structural information about the atom; what we know for sure. We also suspect something else: that subatomic particles are made up of quarks and all particles have anti-particles that, when they collide, release energy in the form of gamma rays.
Elements And Their Cousins. Atoms with different numbers of neutrons are called isotopes. For instance, carbon has fifteen known isotopes, but only three are commonly referenced: carbon-12, carbon-13, and carbon-14.
All three isotopes have six protons (carbon's atomic number), but C-12 has 6 neutrons, C-13 has 7 neutrons, and C-14 has 8 neutrons.
Isotopes are usually written in a form called standard notation, which includes the mass number (A), the atomic number (Z) and the symbol of the element (X).
Mission Objectives: You should be able to...
1. Describe the structure of an atom.
2. Describe the structure of an isotope.
3. Explain the difference between atomic number and mass number.
4. Calculate the average atomic mass of an element.
All neutral atoms contain the same number of protons & electrons. The number of protons determines the element's identity. For instance, 8 protons = oxygen. 17 protons = chlorine. 20 protons = calcium. This does not change.
Electrons determine chemical behavior. Valence electrons (electrons in the outermost energy levels) are significant in this regard, because the number of valence electrons determine how an element behaves in certain conditions. Elements with an octet (8 valence electrons) are unusually stable and do not combine to form compounds (noble gases have an octet, with the exception of helium).
Neutrons determine isotopes. They do not affect the charge or the element's identity. However, they do affect the mass of the nucleus. Several elements have multiple isotopes. Almost every element has isotopes, and what is represented on the periodic table is an average of all of the isotopes of a particular element (which is why the atomic mass is a decimal). In a later mission, you will learn how to use mass spectrum data to calculate relative atomic mass (RAM).
This is basic structural information about the atom; what we know for sure. We also suspect something else: that subatomic particles are made up of quarks and all particles have anti-particles that, when they collide, release energy in the form of gamma rays.
Elements And Their Cousins. Atoms with different numbers of neutrons are called isotopes. For instance, carbon has fifteen known isotopes, but only three are commonly referenced: carbon-12, carbon-13, and carbon-14.
All three isotopes have six protons (carbon's atomic number), but C-12 has 6 neutrons, C-13 has 7 neutrons, and C-14 has 8 neutrons.
Isotopes are usually written in a form called standard notation, which includes the mass number (A), the atomic number (Z) and the symbol of the element (X).
Have you ever wondered why, if atomic numbers represent the number of protons (and, theoretically, neutrons) in the nucleus, and they're assigned masses of 1 each, then why are the given atomic masses on the periodic table decimals? In other words, if the mass number (protons + neutrons) are whole numbers, then why is the atomic number a decimal?
Well, that's because the average atomic mass is the average of all isotopes for any one element. In order to calculate the AAM, you need to know the percent abundance of each isotope (this should be a percentage, which you turn into a decimal), and the atomic mass of each isotope. DO NOT ROUND THESE NUMBERS. You will do your rounding at the very end.
Multiply the percent abundance (now a decimal) by its atomic mass. Do this for each isotope. Then add all the isotopes together. Your answer should equal the value that is listed on the periodic table. (I will be providing you laminated copies of these to keep in your binders next class, insha'Allah)
ChemWiki went hard by demonstrating how to calculate AAM with pictures.
Wanna practice? Of course you do! It's on the exam!!!
Well, that's because the average atomic mass is the average of all isotopes for any one element. In order to calculate the AAM, you need to know the percent abundance of each isotope (this should be a percentage, which you turn into a decimal), and the atomic mass of each isotope. DO NOT ROUND THESE NUMBERS. You will do your rounding at the very end.
Multiply the percent abundance (now a decimal) by its atomic mass. Do this for each isotope. Then add all the isotopes together. Your answer should equal the value that is listed on the periodic table. (I will be providing you laminated copies of these to keep in your binders next class, insha'Allah)
ChemWiki went hard by demonstrating how to calculate AAM with pictures.
Wanna practice? Of course you do! It's on the exam!!!
Let's play around with average atomic mass. Download this handout. We will have to make adjustments because clearly, we don't have M&Ms, Skittles or Reese's Pieces.
Mission 2: Atomic Theory. How did we go from "nothing" to "something" to "something really complex?"
Mission Objectives. You should be able to...
1. Trace the development of atomic theory from ancient times to now.
2. Explain why models have to be revised and refined.
3. Describe how our understanding of the atom has changed over time.
What we know about the atom has changed over time because of technological advances, obviously. The book does not provide enough historical context, so you can add to your knowledge base by reading up on atomic theory. Ask yourself, "How is the ability to understand a fact of nature is limited by our ability to observe it?"
Mission Objectives. You should be able to...
1. Trace the development of atomic theory from ancient times to now.
2. Explain why models have to be revised and refined.
3. Describe how our understanding of the atom has changed over time.
What we know about the atom has changed over time because of technological advances, obviously. The book does not provide enough historical context, so you can add to your knowledge base by reading up on atomic theory. Ask yourself, "How is the ability to understand a fact of nature is limited by our ability to observe it?"
You will track the development and refinement of atomic theory and the models that resulted after each change. You and your group will do a short presentation (5-6 minutes) and write a short reflective essay (one page, double-sided) on your theorist. Keep in mind that the guiding idea for your essay should be: How is the ability to understand a fact of nature is limited by our ability to observe it?
The presentation and essay are due on September ______________________.
Some links to help you are below.
1. BBC Bitesize
2. Modern Atomic Theory
3. Early Atomic Theory
4. Atomic Theory Timeline
Questions you should address in your presentation:
1. Who is your scientist/theorist and what were their scientific qualifications?
2. What specific particle did they study, or did they study the atom in general?
3. What kinds of experiments did they do? Describe in detail.
4. What was the name of their atomic model?
5. Provide a picture of the model.
6. Why did the model eventually have to be replaced, if it was replaced? In other words, models change because they can no longer sufficiently explain certain phenomena. Why did your assigned atomic model have to be replaced?
The presentation and essay are due on September ______________________.
Some links to help you are below.
1. BBC Bitesize
2. Modern Atomic Theory
3. Early Atomic Theory
4. Atomic Theory Timeline
Questions you should address in your presentation:
1. Who is your scientist/theorist and what were their scientific qualifications?
2. What specific particle did they study, or did they study the atom in general?
3. What kinds of experiments did they do? Describe in detail.
4. What was the name of their atomic model?
5. Provide a picture of the model.
6. Why did the model eventually have to be replaced, if it was replaced? In other words, models change because they can no longer sufficiently explain certain phenomena. Why did your assigned atomic model have to be replaced?
Mission 3: Electrons Acting a Fool.
Mission Objectives. You should be able to...
1. Explain why the shell models of the atom are incorrect.
2. Explain the four quantum numbers.
3. Draw orbital diagrams for elements 1 - 20.
4. Write electron configurations for elements 1 - 20.
5. Write abbreviated electron configurations for elements 1 - 20.
As you're learning about atomic theory and the development of the atom, you should discover that most of the models do not specify the arrangement of electrons. JJ Thomson acknowledged their existence, but his model left a lot to be desired in terms of arrangement. Rutherford's model showed the existence of a positively charged nucleus, but does not describe the behavior of the electrons we know existed at that time. Nagaoka's model is similar to Bohr's model in that the electrons orbit the positively charged nucleus, but Nagaoka's model couldn't explain what kept the electrons from falling into the nucleus. Bohr predicted that electrons orbit the nucleus in energy levels similar to how planets orbit the sun. Bohr's model works for hydrogen, but for successively higher atomic numbers, the model fails. The reason the model fails for other elements is because (1) it assumes that the positions of the electrons are fixed, (2) it assumes that energy levels are circular, and (3) it suggests an incorrect size scale for atoms.
Knowing these problems, a newer model for the atom was developed using mathematics and probability. This is due to the fact that there is a level of uncertainty in the location and behavior of electrons, so the previously designed "shell" model no longer works. Heisenberg's Uncertainty Principle says that one cannot know the position and momentum of an electron simultaneously because measuring one quantity changes the other. This means electrons cannot be in set orbits as the previous models describe. They have to be in 3D regions of space called orbitals. Electrons also spin in two directions: positive (up) and negative (down). Therefore, only two electrons can exist in an orbital. This makes it impossible for eight electrons to be in one "shell."
As a result, the Quantum Mechanical Model, which is a mathematical model that is based on the probability of locating an electron, was developed and is the model we currently use today. It is postulated that 90% of the time, electrons can be found in these orbitals, and the behavior of electrons can be described using four quantum numbers: size (n), shape (l), orientation (ml), and spin (ms).
Mission Objectives. You should be able to...
1. Explain why the shell models of the atom are incorrect.
2. Explain the four quantum numbers.
3. Draw orbital diagrams for elements 1 - 20.
4. Write electron configurations for elements 1 - 20.
5. Write abbreviated electron configurations for elements 1 - 20.
As you're learning about atomic theory and the development of the atom, you should discover that most of the models do not specify the arrangement of electrons. JJ Thomson acknowledged their existence, but his model left a lot to be desired in terms of arrangement. Rutherford's model showed the existence of a positively charged nucleus, but does not describe the behavior of the electrons we know existed at that time. Nagaoka's model is similar to Bohr's model in that the electrons orbit the positively charged nucleus, but Nagaoka's model couldn't explain what kept the electrons from falling into the nucleus. Bohr predicted that electrons orbit the nucleus in energy levels similar to how planets orbit the sun. Bohr's model works for hydrogen, but for successively higher atomic numbers, the model fails. The reason the model fails for other elements is because (1) it assumes that the positions of the electrons are fixed, (2) it assumes that energy levels are circular, and (3) it suggests an incorrect size scale for atoms.
Knowing these problems, a newer model for the atom was developed using mathematics and probability. This is due to the fact that there is a level of uncertainty in the location and behavior of electrons, so the previously designed "shell" model no longer works. Heisenberg's Uncertainty Principle says that one cannot know the position and momentum of an electron simultaneously because measuring one quantity changes the other. This means electrons cannot be in set orbits as the previous models describe. They have to be in 3D regions of space called orbitals. Electrons also spin in two directions: positive (up) and negative (down). Therefore, only two electrons can exist in an orbital. This makes it impossible for eight electrons to be in one "shell."
As a result, the Quantum Mechanical Model, which is a mathematical model that is based on the probability of locating an electron, was developed and is the model we currently use today. It is postulated that 90% of the time, electrons can be found in these orbitals, and the behavior of electrons can be described using four quantum numbers: size (n), shape (l), orientation (ml), and spin (ms).
We use the QMM to show how the electrons in an atom are arranged around the nucleus.
Electrons obey three rules in their arrangement. You can read about them here. As atomic number increases, electrons fill energy levels and sublevels in an orderly fashion. The simplest sublevel is "S." The above image shows the S sublevel on the left. The image on the right is the P sublevel. You can look up D and F sublevels. They're really funky-looking. As energy level increases, the size of the sublevel increases. Electrons in the outermost energy levels are called valence electrons. These electrons are the ones that determine chemical behavior.
Homework: Review the videos and take a look at this practice test. See if you can answer the questions. The test comes with an answer key so you can check your work. If there is a reason why you feel you can't answer a question, then that is a question you must ask me during class.
Homework: Review the videos and take a look at this practice test. See if you can answer the questions. The test comes with an answer key so you can check your work. If there is a reason why you feel you can't answer a question, then that is a question you must ask me during class.