Today is Wednesday, September 20 th, 2017

Transcription

1 In This Lesson: Atomic Structure (Lesson 6 of 6) Today is Wednesday, September 20 th, 2017 Stuff You Need: Worksheet Pre-Class: Exactly how big is an atom, would you say? Of what is it made? Take a worksheet!

2 Today s Agenda This is a two day lesson! Day 1: Atoms Subatomic Particles Notation Ions Day 2: Isotopes Calculating atomic mass Isotope Bean Lab Where is this in my book? P. 102 and following

3 By the end of this lesson You should be able to describe the three main components of an atom and what happens when each of these components changes in number. You should be able to calculate atomic mass using a weighted average.

4 How Small Are We Talking? gin/cells/scale/ Scale of the Universe.lnk

5 Aside: You re a Star! Remember the Law of Conservation of Matter? Here s a weird thought since atoms are never destroyed or created (only recycled ), the same atoms that were in stars at the beginning of time are partially in YOU right now! The same goes for our ancestors. It s estimated that around 1 billion of your many atoms once belonged to Shakespeare. Some of the rest may have come from Henry VIII or Julius Caesar or anyone else that died quite a while ago. Also, one more thing that means that most of the water you drink and in your body is recycled dinosaur urine. Yum!

6 Atoms and Subatomic Particles Atoms are the smallest particle of an element that still behaves like that element. Generally, atoms are arranged such that there is a dense center core (the nucleus) surrounded by a diffuse field. In (almost) every atom, there are the following three key subatomic particles: Proton Neutron Electron

7 Aside: Sub-subatomic Particles Below the level of protons, neutrons, and electrons are other subatomic particles. Without going into too much depth: Protons are made of three quarks, two up and one down. Neutrons are made of three quarks, two down and one up. Electrons are made of electrons.

8 On your worksheets Look to #8 on page 1.

9 Subatomic Particles Protons Location: Nucleus Charge: Positive Mass: 1 amu Symbol: p + Discovered by: Eugen Goldstein

10 Subatomic Particles Neutrons Location: Nucleus Charge: None Mass: 1 amu Symbol: n 0 Discovered by: James Chadwick

11 Neutrons

12 Okay, one more Why can t you believe atoms? Because they make up everything! Ishaan D. (September 2013)

13 Another, you ask? What did one atom say to the other atom? Do these protons make my mass look big?

14 Subatomic Particles Electrons Location: A cloud around the nucleus, moving at high speeds Actually, VERY FAR from the nucleus, too. Charge: Negative Mass: 0 amu (so small it s rounded to virtually nothing) Symbol: e - Discovered by: JJ Thomson

15 Aside: Empty Space Okay, so you notice how most of the atom is empty space? It turns out that nothing, really, is solid in our everyday lives. Your chairs, your desks, your notebooks, YOU - they re all mostly empty space. In fact, when two objects come in contact with each other, they actually don t. What I m saying is you re not actually touching your chairs right now. Two objects that collide are actually just experiencing electrons repelling one another. Without this force, a bowling ball would go through the pins. Cosmos Atoms

16 Anyway Take a look at your periodic tables. We re going to do a little exercise with em.

17 Dmitri Mendeleev The inventor of the modern Periodic Table: Trimmed his beard and hair once a year. For reals.

18 Atomic Rules 1. Is there a relationship between the number of protons and neutrons in an atom? What about protons and electrons? 2. Compare atomic number (that s above the symbol and below the name) to the number of protons in the element. 3. What about atomic mass? How might that be calculated?

19 How Many p +, n 0, e -? Protons (p + ) Represented by the atomic number. Neutrons (n 0 ) Mass number minus atomic number. Electrons (e - ) Same as the number of protons in neutral atoms. Mass number Protons + Neutrons Can be written as either Na-23 or 23 Na. Mass Number Atomic Number

20 Atomic Notation With all these statistics, the formal notation of these atoms can be confusing. Here s an example of the nuclear symbol:

21 How Many p +, n o, e -? How many protons, electrons, and neutrons are in the following atoms? 9 Be 4 Protons = 4 Electrons = 4 Neutrons = 5 20 Ne 10 Protons = 10 Electrons = 10 Neutrons = Cl 17 Protons = 17 Electrons = 17 Neutrons = 18

22 On your worksheets Take 6.57 minutes and try #1-3 and 5. For #1, leave out: Atomic Mass Isotope Isotope Name For #5, leave out: Isotope Name NOTE: Atomic mass/weight and atomic number are different. DO NOT use atomic mass or atomic weight for now.

23 For a little practice we re going to build some atoms with our computers using one of two methods: PhET Build an Atom ExploreLearning Element Builder

24 PhET Visit this website (listed in my Chem Links page): Once here, click Run Now. When the applet loads, hit the + signs on the right side next to Symbol, Mass Number, and Net Charge. Then, start building atoms by clicking and dragging subatomic particles to the appropriate places.

25 [Log-in Instructions] Element Builder

26 Build Your Own Elements Build the following elements (don t forget all the subatomic particles): Hydrogen, Oxygen, Lithium, Carbon Questions to ponder: What happens when you change the number of protons? What happens when you change the number of neutrons? What happens with you change the number of electrons?

27 Changing Protons Changing the number of protons changes the element. In other words, the atomic number of an element never changes. It is always equal to the atomic number.

28 Changing Neutrons Changing the number of neutrons in an atom changes the mass number, creating a new isotope. Isotopes are atoms of the same element that have different mass numbers. Example: Carbon always has 6 protons. Sometimes it has 6 neutrons, sometimes it has 8 neutrons. Thus, Carbon (mass 12) and Carbon (mass 14) are isotopes.

29 Famous Isotopes: 235 U

30 Famous Isotopes: 14 C

31 Isotope Names Isotopes are often written like this: Carbon-14 (meaning Carbon with a mass number of 14). Or like this: C-14 (meaning the same thing) Or like this: 14 C (meaning the same thing)

32 On your worksheets Take 1.1 minutes and try #1, 4, 6, and complete #5. For #1, leave out Atomic Mass.

33 Changing Electrons Neutral atoms have the same number of protons as electrons, balancing the charges. Changing the number of electrons creates an ion. An ion is an electrically-charged atom and can be positive ( + ) or negative ( - ). Atoms that lose electrons are called cations and have a positive charge. Atoms that gain electrons are called anions and have a negative charge.

34 How to Remember Cations (positive) I like cats that s a positive statement! CA+ION Anions (negative) A negative ion anion.

35 Ions If an atom has more electrons than protons, it has a negative charge. If an atom has fewer electrons than protons, it has a positive charge. Example: Hydrogen has one proton and one electron. If we take away an electron, hydrogen becomes positively charged.

36 Determining Charge To figure out the charge on an ion, find the number of protons and electrons. Use the following formula: [protons] [electrons] = CHARGE Example: Lithium (atomic number 3) with 5 electrons: 3 5 = Charge of -2 (Li 2- )

37 Ions Write ions by writing: Element abbreviation How positive or negative they are in superscript Example: Helium with 4 electrons (instead of 2) is He 2-. For both negative and positive ions with a difference of one electron, just write + or appropriately.

38 Ions Example: Hydrogen normally has 1 electron. If it has no electrons (positive charge) we would write it as H +. If Hydrogen has 2 electrons (negative charge), we would write it as H -.

39 Building Ions Let s build some ions using the computer: H + Li 2+ C - O 3- The only way to make ions is with electrons.

40 So, do you get this cartoon?

41 Just when you thought it was over What s the difference between a seal and a sea lion? An electron. Anthony H. (October 2016)

42 One last thing You may have noticed that in all of this PowerPoint I only mentioned the term atomic mass once, but I have used the term mass number many times. There s a difference!

43 Calculating Atomic Mass By now you know that isotopes are atoms of the same element with different masses. Those masses, calculated by adding protons and neutrons (which each weigh 1 amu), are called mass numbers, and they re different for each isotope. 1H 1 1H 2 3 1H

44 How Many p +, e -, n 0? Determine the number of protons, electrons, and electrons for each isotope: C-12 and C-14 C-12: Protons = 6; Electrons = 6; Neutrons = 6 C-14: Protons = 6; Electrons = 6; Neutrons = 8 O-16 and O-18 O-16: Protons = 8; Electrons = 8; Neutrons = 8 O-18: Protons = 8; Electrons = 8; Neutrons = 10

45 Atomic Mass Atomic mass, however, is the weighted average of all the element s isotopes atomic masses based on their abundance. It s not a simple average. It s actually quite like the way your grades are calculated. (remember the 50% / 40% / 10% scale?) To learn atomic mass, we ll first learn how you can calculate your chemistry grade.

46 Atomic Mass: Weighted Averages Let me introduce you to Rembrandt Q. Einstein, a student in chemistry. His test average is 90, quizzes/lab/project average is 100, homework is 50. If tests are worth 50%, quizzes (etc) 40%, and homework 10%, what is Rembrandt s grade? 90 * (0.5) * (0.4) + 50 * (0.1) = 90 First category First category Second PLUS category Second Third PLUScategory Third category EQUALS average weight (decimal) average weight (decimal) average weight The (decimal) Weighted Average

47 Good to Know Rembrandt s weighted average grade is a 90%. What s his simple average grade? 80%. The fact that Rembrandt s most important grades are good ones raises his average above what it would have been.

48 Atomic Mass: Weighted Averages To calculate atomic mass (remember, it s a weighted average too), use the same procedure as for your grades. Mass of Isotope 1 * Abundance of Isotope 1 (decimal) + Mass of Isotope 2 * Abundance of Isotope 2 (decimal) Let s try a sample problem.

49 Atomic Mass: Weighted Averages What is the atomic mass of silicon if 92.21% of its atoms have mass amu, 4.70% have mass amu, and 3.09% have mass amu? (.9221) (.047) (.0309) =? First isotope First isotope PLUS Second isotope Second isotope PLUS Third isotope Third isotope mass abundance (decimal) mass abundance (decimal) mass abundance (decimal) Silicon s atomic mass is amu.

50 Atomic Mass: Weighted Averages Find the average atomic mass for silver if 51.83% of its atoms have mass amu and 48.17% of its atoms have mass amu (.5183) (.4817) =? First isotope First isotope PLUS Second isotope Second isotope mass abundance (decimal) mass abundance (decimal) Silver s atomic mass is amu.

51 On your worksheets Complete #1, #7, and the reverse side.

52 Tonight s Assignment You may work alone or with a partner. Research two additional scientists in the history of the development of the atomic model. Prepare a PowerPoint with a timeline including scientists from class and that you have researched. Don t forget to use your textbook! Requirements and rubric posted online!

53 Now for a lab Get your worksheets we re going to start the Isotope Bean Lab!