CEM 141 Chapter 1 Notes PDF

CEM 141 – Chapter 1 Note: This is a condensed set of notes that does not contain everything your instructor will present in class. You should add to these notes during the lecture! 1. Make sure to record answers to questions/polls, explanations, and drawings. 2....

CEM 141 – Chapter 1 Note: This is a condensed set of notes that does not contain everything your instructor will present in class. You should add to these notes during the lecture! 1. Make sure to record answers to questions/polls, explanations, and drawings. 2. Write down any questions you have so that you can ask at the end of the lecture, during  CEM 141 – Chapter 1 Note: This is a condensed set of notes that does not contain everything your instructor will present in class. You should add to these notes during the lecture! 1. Make sure to record answers to questions/polls, explanations, and drawings. 2. Write down any questions you have so that you can ask at the end of the lecture, during office hours, or in the chemistry help room. What is chemistry?  Grab a piece of paper! 1. What do you think you will learn about in this course? 2. What wouldLoading… you like to learn about in this course? Science is amazing and counter-intuitive and sometimes downright weird! The universe emerged out of nothing about 13.8 billion years ago. Most of the atoms in your body were formed in stars. Matter is composed of atoms that are mostly empty space. Energy and matter are versions of the same thing. Matter can be a particle or a wave. Atoms and molecules can interact to produce something that has emergent properties (different than the sum of the reactants). Molecular level structure determines the observable properties of “stuff”. Increasing entropy can produce complex, self-organized structures. A collection of cells can, by itself, produce a self-conscious entity that thinks it is more than a collection of cells.  How do we know all this? Just so youLoading… know, there is no such thing as “the scientific method”.  Scientists (that’s us!) 1. Ask _________ questions 2. Design ___________ experiments 3. Gather and analyze ____________ data and evidence 4. Make _______ claims (based on data and evidence) 5. Develop ________________________ modelsexplanations , , and about theories how and why the universe behaves as it does We will do many of these things this semester!  Is this a scientific question? (testable + measurable) 1. What temperature A. Yes, this is a will my coffee be if I scientific question add milk to it? A B. No, this is not a 2. Do dragons have scientific question wings? B C. I don’t know! 3. Can my dog understand what I say? < needs clarification  Scientific Questions Scientific questions can be answered by: doing experiments making observations taking measurements All must be done ______________ in areplicable way. (If someone else can’t _______ repeat it then it is not science!)  Activity Design an experiment to answer the question: “What temperature will my coffee be if I add milk to it?” – What procedure would you use? – What materials do you need? – What observations would you record? Write down your answers because this is the first question in your homework! I’ll also ask how and why the coffee changes temperature.  What did you predict? What will happen to the temperature of the hot coffee if you add cold milk to it? This is your ______! claim  Every claim must be supported with evidence. What evidence do we have for the existence of atoms? What is the evidence that there is an attractive force Loading… between objects with mass? gravity - What is the evidence that all life is descended from a single cell? -cellreproduction What evidence do you have that coffee gets colder if you add milk? ↳ temp.  Every claim must be supported with evidence. Claim: If I add cold milk to hot coffee the coffee will cool down. This must be supported with evidence. Evidence comes from your experiment: For example: The temperature of the coffee/milk mixture was 10°C lower than the temperature of the coffee alone. With a lot of evidence, you might be able to construct a model:  A Scientific Model Can be a drawing or a graph or a diagram or an equation, physical or mental. We use models to help us make sense by – Predicting what will happen. They make testable, quantifiable predictions. – Explaining how something happens (HW part 2). We could imagine lots of different models that would help us understand the addition of cold liquid to hot. Some Atomic Models In addition to developing a model, we can use our claim and evidence to develop an explanation. Scientific explanations and scientific theories help us explain why. There are many levels of detail possible. You should aim for the most complete explanation that you can produce. Extra: Watch Richard Feynman explain why it is difficult to explain “why”  Constructing a Scientific Explanation If you are asked to explain something you will need three parts to the explanation: 1. Claim: the target of your explanation. 2. Evidence: the data or scientific principle you are using to support your claim. 3. Reasoning: the connection between your claim and evidence. For example: Why does your hot coffee cool down when you add cold milk to it? In other words, what is causing the coffee to get colder?  Explain why coffee cools down when milk is added. Claim Coffee cools down when milk is - added Evidence because the temperature of the coffee/milk mixture is lower than that of coffee alone. Reasoning The coffee molecules (with higher ↑ constructing kinetic energy) collide with the milk un exam molecules (with lower kinetic energy) and transfer energy. Because the coffee molecules now have less kinetic energy, their temperature is  A Scientific Theory The ______________________ best available explanation of the existing evidence/data/observations. Explains _____________. now and /or why Makes _______________. testable predictions Is falsifiable (ie can be proven false by experiments and data). May change ___________ as new evidence becomes over time available. What scientific theories have you heard of? What is the difference between Law and Theory? A law describes the phenomenon. A law tells you what. A theory explains the phenomenon. A theory tells you why.  Questions, Facts, Laws, Hypotheses, and Theories Big Bang = Theory Which of theA. Special relativity (time and space following is are not absolute but are relative to a… each other) B. The force of attraction between Fact C masses is proportional to the product Law D of the masses, and inversely Hypothesis d proportional to the square of the distance between them. Theory a C. An atom of hydrogen has one Question e proton. D. If we add reagent X to a reaction it will go faster. E. What will happen if we add X to the reaction? Atoms In 1963, Nobel Laureate Richard Feynman (1918-1988), one of the most accomplished and influential scientists of the 20th century, wrote: “If, in some cataclysm, all of scientific knowledge were to be destroyed, and only one sentence passed on to the next generation of creatures, what statement would contain the most information in the fewest words? I believe it is the atomic hypothesis (or the atomic fact, or whatever you wish to call it) that all things are made of atoms—little particles that move around in perpetual motion, attracting each other when they are a little distance apart, but repelling on being squeezed into one another. In that one sentence, you will see, there is an enormous amount of information about the world, if just a little imagination and thinking are applied.” What do you know about atoms? (Make a list) made from them -all things and neutron - includes neutron , proton , small , blind to human eye - extremely Did you know that only about 5% of the mass and energy in the Universe appears to be made of atoms (or parts of atoms)?  Which has atoms in it? Heat A. All of them Cells B. Cells and Gold Air C. Cells, Air, and Gold Gold D. Only Gold  Which is biggest? A. An atom B. A molecule C. A cell D. It depends How big do you think an atom is? and convert * know A. About 0.1 centimeter (0.1 × 10–2 m) B. About 0.1 millimeter (0.1 × 10–3 m) C. About 0.1 micrometer (0.1 × 10–6 m) D. About 0.1 nanometer (0.1 × 10–9 m) E. About 0.1 picometer (0.1 × 10–12 m) The Scale of the Universe  Learning Objectives Found in the “Learning Objectives” folder on D2L Big Ideas Loading… – Framework for organizing what you learn in CEM 141 – The same big idea will appear multiple times throughout the course. Learning Goals – Specific things that you should be able to do with your knowledge Scientists claim that atoms exist. What is our evidence? * techniques that help us see We can now actually “see” atoms. Atomic Force Microscopy /AFM) ↑ allows us to see location of electichs + atos  evidence * techniques provide don't need to know how Atomic force microscopy (AFM) - and scanning tunneling microscopy (STM) provide images at the atomic * detects of a tors level pos. Extra: AFM manipulated CO molecules  Atomic Theory Development Where did the original idea of atoms come from? ___________ The Greeks Was this a Scientific Theory? (In other words, was it based on experiments, data, and evidence?) Not a St ; emerged from philosophy  Development of Atomic Theory ___________: Greeks earliest atomic theory – Based on ____________, philosophy not ________________. experimental evidence – The movement of specks of dust in the sunlight led to the conclusion that atoms were in constant motion with nothing, or a “void”, between them. The random motion of atoms and particles was later called Brownian motion – Brownian motion at the atomic level (cartoon) – Brownian motion at the macroscopic level “Atomos” – not to be cut ↳ indivisable  – Elements: Earth, fire, air, and water The Greeks believed that the shape of atoms determined their properties. If “earth” had atoms that were cubic, what shape would you ascribe to the Greek elements “water” and “iron”? This was not correct, but it foreshadowed the idea that the molecular level structure of a substance determines the observable properties.  Questions What properties ascribed by the Greeks to atoms do we still consider to be valid? in constant motion atoms are If atoms are in constant motion, what do you think keeps them moving? enermal energy  Elements An ______ a tom is the smallest unit of an _______. element Atoms of different elements are different. How? of protons properties - # & , type , atom identified by this 91 (or 98) elements are naturally occurring (number is arguable and not a detail we’re interested in). Elements ordered in the periodic table.  We will come back to the # of element's periodic table often! protons L & symbol & mass #  How would you explain the difference between an atom and an Gold atoms element? Elemental gold (gold ore) Individual nanoscale entities Collection of gold atoms Too small to see with eye Macroscopic sample Very different ________! properties  Choose the correct answer: (0) oxygen atom A. 2 1. An atom of an element 2. A molecule of an element H20 7 B. 2 3. A molecule of a compound I made diff of of tums) a types C.. 4. An atom of a compound Hy 7 D. That’s impossible  Questions to Answer After Class 1. What distinguishes one element from another? How do the atoms of different elements differ? (How do we know?) 2. What types of evidence might be used to conclude that you had isolated a new element? 3. What types of elements would be difficult to identify? 4. What is the difference between an atom and a molecule? 5. What is the difference between an element and a compound? What is the structure of the atom? (What does an atom “look like”?) What evidence do we have to support this claim?  Dalton’s Atomic Theory ① Elements are composed of small indivisible, indestructible particles called atoms. ②All atoms of an element are identical and have the same mass and properties. ③Atoms of a given element are different from atoms of other elements. ④Compounds are formed by combinations of atoms of two or more elements. John Dalton published his theory in 1808. ⑤Chemical reactions are due to the rearrangements of atoms; atoms (matter) are neither created nor destroyed during a reaction.  Dalton’s Atomic Theory Elements are composed of small Is this tenet of indivisible, indestructible particles otopes called atoms. B is Dalton’s Theory All atoms of an element are identical L still considered to be and have the same mass and properties.B true today? Atoms of a given element are different from atoms of other elements. A Compounds are formed by A. Yes combinations of atoms of two or more B. No elements. A Chemical reactions are due to the C. I don’t know rearrangements of atoms; atoms (matter) are neither created nor destroyed during a reaction. A > - not correct , it's shape of molecules  Atoms Have Sub-Structure Which subatomic particle was discovered first? (and why do you think this is so?) -reading A. Proton B. Electron< discovered first Do it has a charge - C. Neutron - location/easier to Make sure to watch the access D. I don’t know following videos before our next class: J.J. Thomson video · ↳ Founder Rutherford video 47  How to Succeed in CEM 141 Actively participate in class activities! During class, take notes. Review your notes, the lecture slides, and the learning objectives after every lecture.  How to Succeed in CEM 141 Take notes. Don’t just write down information from the slides; instead, write down the things we discuss that are missing. Actively participate in class activities! Review your notes and the learning objectives after every lecture. Add to the slides that we give you! Write out answers to questions and explanations that aren’t in the slides. Draw pictures and structures – if we write it down, so should you! Record answers to the polling questions! Write down your questions and bring them to the help room. One of the best things you can do to succeed in this class is to review your notes after every class, before we meet again.  How to Succeed in CEM 141 Do your homework and evaluate it in class. – Write down your answers as you complete the activity. – Bring your answers to class and make corrections when we discuss the activity. – Answers to the homework will not be posted. You learn best when you can make connections (what is similar and what is different) between what we are currently learning and what you have previously learned. ↓ important resources fun de  There is a document on D2L with more How to get the most out of your beSocratic homework Complete every HW assignment. To earn credit, it must be clear that you made an effort. Write down your answers on paper or take a screenshot of each slide before you move on. – If you take screenshots, print them out. In class, criticize and “correct” your answers. This is your chance to get feedback and improve. Repeat assignments that you had trouble with when studying for the exam. – These are under the “Practice Activities” tab. Additional notes on the things we talk about while going over the HW in class. Improving and “correcting” answers. The Electron: Discovered by JJ Thomson (Nobel Prize 1906) & discovered electron Evidence for the existence of electrons  Discovery of the Electron for being (Evidence) atoms S dividable and Cathode ray tube: glass tube consisting of two electrodes under very low pressure. When a high voltage is applied, cathode emits “particles” that move toward anode. beam of electrons 2 I * to allows beam through towards plate go Particle ray bent toward (+) plate. The type of metal that the cathode was made of did not affect the (The particles were also deflected by magnetic fields.) behavior of the ray. Mass of particle was about ~1/2000 that of H atom.  Question What is the evidence from Thomson’s experiment that all atoms contain electrons? A. The particles were attracted to the + electrode. B. The particles were deflected by magnetic fields. C. The particles were deflected by electrical fields. D. The particles were identical regardless of the metal used for the cathode (where they were emitted from). Thomson’s “Plum Pudding” Model of the Atom Description: Atoms contain electrons "embedded" in a positively charged blob electron I a picture of the model).[ This is a plum pudding (not This is the model. jThis is a chocolate chip cookie (also not a picture of the model). visans terresta i ros Atoms have electrons, but where are they? Are there any other particles in atoms? Ernest Rutherford (Nobel Prize 1908) Evidence for the existence of the nucleus Rutherford’s Experiment > - gad fail * alpha particles went straight through * %000 defected/bounced back  What is an alpha particle? An alpha particle has 2 protons and 2 neutrons. It is the nucleus of a helium atom. proton L neutron ↳ + 2 charge  Plum Pudding Atom if atom was like a plum pudding, - J J. all the α particles should go straight through a few of the α particles Nuclear Atom do not go through. most α particles go straight through -. * led to nucleus. discovery + charged some α particles are deflected Play with the Rutherford applet  Rutherford’s experiment showed: Atom is mostly ________. empty space" Greeks said this ___________________ small densepositive in the center of the nucleus atom. t - bc alpha is something + and repelled Play with the Rutherford applet http://phet.colorado.edu/simulations/sims.php? sim=Rutherford_Scattering Rutherford’s Planetary Model incorrect model but led to nucleus discovery - ,  Neutrons (discovered 1932) Harder to detect! Why? S no charge nucleus and in the neutral in - charge-not manip. W/ electric Reside in nucleus. Slightly heavier than protons. What does the atom “look” like?  Model of Atom We Will Use For Now: Electrically neutral Very small nucleus A helium atom (~2 × 10–15 m) contains – Protons (+1 charge, 1 amu) – Neutrons (0 charge, 1 amu) “Cloud” of electrons – takes up most space 4 vea (~20 – 200 × 10–12 m) – Electrons (–1 charge, ~ 1/1800 amu) Atom Interactions We can explain how atoms interact using the idea that opposite charges attract and like charges repel. (Coulomb’s Law) But first, what is an interaction? An interaction is a force! What is a force? A push or a pull What forces do you know? (make a list) force magnetic - -gravitational force  The 4 Fundamental Forces We have the most experience with this force. crecisea Force Description for Gravit mass Gravity Responsible for attraction between objects that have mass. Responsible for attraction/repulsion between Electromagnetic charget objects that have electric charge. Short range interaction that occurs between objects made of quarks (like protons and neutrons, Strong Strong which are held together in the nucleus despite electrical repulsions between protons). Short range interaction that occurs between Weak elementary particles; weaker than electromagnetic But this is the or strong force. force that we need to understand.  Here is Matt. He has thrown a ball in the air. What forces are acting on the ball once it is in the air? A. Gravitational B. Electromagnetic C. An upward force from his hand D. There are no forces because nothing is touching the ball E. A and C  If you’re having trouble thinking about how mass and distance affect gravity, click here! What happens to the gravitational force of attraction as: 1. The mass of the interacting objects increases? A * 2. The distance between the objects increases? B A) Force increases B) Force decreases  Newton’s Law of Universal Gravitation can be modeled by this Gravitational equation: mass of farce (There is also a Objects ↓ ↓ ↓ M Mz proportionality Fy , uz constant that we will * distance ignore for now.) Example of inverse-square law. As r increases, F decreases by a factor of 1/r2.  How do you think the gravitational force of the earth is able to influence the ball even though the ball and the earth are not in contact? "minute physics" explains gravity ↑ ↑ Gravitational Forces are Mediated by Gravitational Fields Objects with mass are sources of gravitational fields and are affected by the gravitational fields of all other objects with mass. Gravitational forces require __________ 2 + objects. Earth-moon gravitational field Gravitational forces are always ________. attractive  The Electromagnetic Force is Mediated by Electric and Magnetic Fields magnetic fields electric field Electromagnetic forces act at a distance.  The electromagnetic force is much stronger than gravity and can be both attractive and repulsive. - difference We will only consider electric fields and forces between charged staticparticles right now – this is a wespecial case of the electromagnetic  force and is called the electrostatic If you want an electrostatic force challenge, click here! 1. If two objects have A. They repel each other the same charge B. They attract each what happens? A other C. Nothing 2. If two objects have D. I don’t know opposite charges what happens? B  Unlike charges attract Like charges repel Coulomb's – + Law + + The force between the charges can be modeled by using Coulomb’s Law: ↑ charges Force charges = 9 Where q1 and q2 are the F ,9 charges, and r is the distance between them & electrostatio distance furce  Oh look! Both of these interactions FMM follow an inverse square law. Gravitational attraction between masses Don’t get them mixed up! The electromagnetic Fg9 ,9 (electrostatic) force is much Electrostatic attraction between charged stronger and can be attractive particles and repulsive. Gravitational forces are too weak to be detected at the atomic/molecular level.  Here is Mariam. She has a ball in her hand. What forces are acting on the ball? pulling ball down electrons - repelling A. Gravitational Crepulsive) V B. Electrostatic S stops from it O C. Both A and B falling through D. There are no forces because the ball is not moving E. I don’t know The electrostatic force stops us from falling through the Earth… Loading… and makes us hover over chairs (sort of). * electro reprisive D If something is not moving, either there is no force acting on it OR the forces acting on it are equal and opposite. We can stand on the earth because the force of gravity is equal (and opposite) to the electromagnetic force. How do forces influence energy?  What is Energy? “...in physics today, we have no knowledge of what energy is.” … “We know how to calculate its value for a great variety of situations, but beyond that it’s just an abstract thing which has only one really important property. If we add up all the values before something happens and then add them up after it happens the two values will be exactly the same. (We must be sure to include every object affected.) This is the law of conservation of energy”.  What is Energy? We don't know - but definitions circulate What we do know: – Any change in matter is accompanied by a change in energy (Chapter 3) D– Changes in energy are caused by changes in forces – Energy is conserved – (of course this depends on the system you define) Units SI - Joule (kg m2 s–2) 1 calorie = 4.184 J  Systems To study energy changes, we msut define what we are studying – __________ – part of the EX : lab system experiment -> is the System beaker w/ universe you are looking at N – __________ – everything else in > other things - near surroundings the universe beaker the Can monitor energy changes between system and transferred surroundings Trans formed inermo of Ist Law What kinds of energy do you know? (make a list) - Kinetic - Potential - sound - Gravitational - Nuclear Solar -  Kinetic Energy The energy associated with _________ motion KE = ½mv2 -v V mass velocity Kinetic energy  Here is Betoul. The ball is falling down. As the ball moves toward the ground what happens to the kinetic energy? A. O Increase B. Decrease C. Stays the same D. Don’t know Why? [ ON EXAM bic increases velocity - * GF increasing + slide abt A face > A energy -  Potential Energy Sometimes called “stored energy” but that is misleading. – Potential energy is not stored within a single object, but we can think of it as being stored in a field. Potential energy is the energy associated with the position of a system of objects in a field. – There must be two or more objects. – There must be a field (gravitational, electric, magnetic). , so does When the position of two object in a field sys  changes, so does the potential energy of the Here is Betoul again, the ball is falling down. As the ball moves toward the ground what happens to the potential energy of the system (ball + Earth)? A. Increase B. O Decrease C. Stays the same D. Don’t know Why?  Here is Betoul again. The ball is falling down. What causes the potential energy to decrease? A. The kinetic energy increasing O B. The change in position between the ball and earth in the gravitational field C. The weight of the ball D. Don’t know if ↓creases Why does the PE decrease [ the ball is moving forct With the  instead of increase? Here is Betoul again. The ball is falling down. What causes the ball to fall down? ↳ same as reason potential A. The potential energy the of the system Dic decreasing -pall m ine + wi B. The kinetic energy increasing O C. The gravitational interaction between the Earth and the ball D. Don’t know  Here is Betoul again. The ball is falling down. As the ball moves toward the ground what happens to the total energy of the system (ball + Earth)? A. Increase B. Decrease O C. Stays the same D. Don’t know Energy can be…. transferred (from one object to another) and transformed (eg from potential to kinetic energy) Newton's Cradle 99 We have spent a lot of time thinking about forces and energy. What does this have to do with chemistry? 100 Atoms are made up of charged __________! particles elections (- 1 and protons ( ) + Therefore, the electrostatic force is important! We can understand atomic interactions in terms of Coulombic attractions and repulsions  attractions and repulsions. Clearly there must be some mechanism by which atoms stick to make together… molecules , to make scrids from liquids (freezing) (condensation to make liquids from gases Let’s start simply: noble gase Helium (and all the noble gases) do not react with anything. ~ Let’s start simply: Helium (and all the noble gases) do not react with anything. He has a melting point of 0.95 K (–272.2 °C) and a boiling point of 4.5 K (–268.5 °C). liquid gas As we will see, this means something must make the atoms stick together…  States of Matter Activity 1. Draw three boxes on your piece of paper. 2. Using circles to represent helium atoms, draw helium as a solid, a liquid, and a gas. 3. Think about any differences in your drawings? Why do the atoms stick together sometimes but not all the time? 7 8698 He(s) He(l) He(g)  Phases of He slide prior 3 boxes Gas – in reality you would only see ____ particle in this volume one have to show at least 2 in drawings To have solids and liquids, atoms must stick together. What makes the atoms stick Remember, atoms are composed together? of charged particles.  Unlike charges attract, Coulombs like charges repel Law – + + + Review: What does this mean in terms of potential energy? increasesang electrostatic repulsion Dicinstcce N ag ~ plame S - - PEnar no zero · r M electrostatic distance attraction M 7 - PE is distance Our Atom Has a positively charged nucleus Has a negatively charged electron cloud Think of the electron cloud as “fluffy” It can fluctuate momentarily so that the electron density is distorted.  - London Dispersion Forces - - - - - - - nonpolar nonpolar cartial a + om atom I -6 - S + ↓ < - random distortion --- -- - dipose nonpolar atom ~ z S + S- S + S - - · - - - > cause for atoms induced dipole inst. dipole LDF formed >sticking together  all exists btwn ?? ↳ nable gasest London Dispersion Forces > - - ↑ LDE Formed > attracts - + election cloud Still S can Shift (random) How many He atoms must be present for LDFs to exist? A. None B. One LDFs exist between ALL neutral atoms and O C. D. Two or more I don’t know molecules in the solid and liquid states. What happens when two atoms of Ne approach each other?  What happens when two atoms of Ne approach each other? As these two Ne atoms come together, what happens to the electrostatic force? O A. B. Increases Decreases partialfromare C. Stays the same charges m at dipares met Why? [ D/C ze distanc F 9 92 , decrease 8 r2  The attractive Coulombic interaction causes the atoms to approach… …but if they get too close, the electron clouds overlap and the repulsive force becomes dominant. M ~ How do these forces affect the PE?  Let’s construct the potential energy curve as two Helium atoms As the atoms approachapproach each A. Increases other the potential energy B. O Decreases ____________. decreases C. Stays the same D. I don’t know As the atoms move very close together the potential energy __________. increases s moving against farce repulsive  - · - PE -Starts  As the atoms move even closer, which force is strongest? A. A Electrostatic attraction B. B Electrostatic repulsion C. C Gravitation D. D ES attraction = ES repulsion At the potential minimum, which force is strongest? A. A Electrostatic attraction As the atoms move toward B. B Electrostatic each other, which force is repulsion strongest? C. C Gravitation A. Electrostatic D. D ES attraction = attraction ES repulsion B. Electrostatic repulsion & most stable C. Gravitation solid or liquid D. ES attraction = ES repulsion * As the atoms move even closer, the PE increases (because they are moving against the repulsive force). M When they get too close together, the repulsive repulsive force becomes strong is dominant enough to push the atoms apart. At the potential minimum, the system is most stable. The attractive forces = the As the atoms move repulsive forces. together, the PE decreases (because they are moving with the attractive force). F What happens as two helium atoms approach each other? RE ↑ as mored they when closer , dropped repulsive became dominant.  What is different about these three sets of atoms? C 200 pm Where are they on the PE curve? A 120 pm P o te C n A ti al B E 150 pm n e B r g y  As the helium atoms initially approach what happens to: 1. The total energy A. Increases (why) c conserved < energy B. Decreases 2. The kinetic energy C. Stays the same attractive (why) As D. Don’t know faceasembring faster 3. The potential energy moving w/ the (why) BS electro attraction / with the farce  As the helium atoms get very close (overlapping electron clouds) what happens to: 1. The total energy A. Increases C energy (why) conserved B. - Decreases 2. The kinetic energy C. Stays the same repulsive taking (why) BE over + D. slowing KE Don’t know down 3. The potential energy (why) Atdominant:repulsia Why don’t the He atoms stay in this potential minimum? bic bouncing energy How can we get them to stay in the potential minimum? need less energy/ be needs to removed > - other molecule comes and some energy goes to the atom that came  Make sure you can answer these questions about helium atoms 1. interacting! Why do the atoms move toward each other? 2. Why do they oscillate? (go back and forth) 3. What does it take to form a stable interaction (where the atoms don’t fly apart)? 4. What does that third atom do? (watch carefully)  What can the the position of the PE well on the x-axis tell you? A. JThe distance between the atom centers at their most stable point B. How much energy would be needed to overcome the interaction C. Nothing  we e we · areen What can the the depth of the PE well tell you? A. The distance between the atom centers at their most stable point des B. * How much energy would be needed to overcome the interaction C. Nothing  What would we have to do to break the LDFs between the He atoms (and get them out of the potential Add : energy well)? In the "real world", how would energy normally be removed (or added) from the two atoms? - A temp the ↑ temp energy = more When you change the temperature of the system, where does the energy come from/go? < collisions ↳ to remove energy cald plate put on  What happens when you add thermal energy to the helium atoms (raise the temperature)? 3 more ment What happens when you add thermal energy to the helium atoms (raise the temperature)? Why? there's greater movement in the atoms surrounding : collide we system Kinetic energy is transferred to the atoms upon collision, causing them to move faster (because they have more KE). When a collision transfers enough KE to the two He atoms in our system, the attractive force between them is overcome and they fly apart.  What is the relationship between thermal energy and temperature? Thermal energy is a measure of the sum of the kinetic energies (½mv2) of all the atoms. Temperature T is directly related to average kinetic energy (½mv2) of the atoms.  How do the He atoms in the system “know” the temperature is increased? A. The air is warmer and warms the He atoms. O B. The energy is transferred from other atoms that have collided with the walls of the container (that were directly heated). C. The atoms in the system move faster when the temperature increases. D. The heat atoms bump into the He atoms. 140 Back to atomic interactions…  Which statement about the breaking of an attractive interaction between two atoms is true? (simulation) * me adding energy break to into systema part magnets A. Energy is released. < out of system B. Energy is absorbed. c system into C. Energy is released or absorbed depending on the polarity. any - break you time interaction an D. Energy is released or absorbed depending you put energy on the strength of the interaction beingsystem into the broken. Which has more electrons: He or Xe? He has __ 2 electrons, Xe has __ 54 ~ the on average are electrons farther weaker therefore ↓ more polarizable / shifts more floppier ↓ partial larger charges The electron cloud in Xe is  Compared to He, the London Dispersion Forces between Xe atoms are expected to be __________. stronger S g + + 55. >t - O A. Stronger He He LDF B. Weaker St 8 " C. The same S 5 75 : St - S & +, & D. Don’t know Coloumbs Law induced xo ↑ Xe instant-Vg , 927 F LDF CO r2 A cloud IDFILDE larger = larger charges  & London Dispersion Forces Increase with size of atom/molecule (number of electrons) Increase with surface area < Long thin Stronger + : (DF Part of a range of intermolecular forces (between particles) The points above allow you to make predictions. They do not explain WHY one molecule would have stronger LDFs than another.  Which do you think would have the higher melting and/or boiling point? WHY? A. He overcome B. Xe requires more - energy to LDF bonds C. Same D. Don’t know Helium has a melting point of ___, 1k and xenon has a melting point of ___. 161K Was your prediction correct? Let’s bring this back to PE diagrams.  What can the the depth of the PE well tell you? A. The distance between the atom centers at their most stable point B. How much energy would be needed to overcome the interaction C. Nothing deeper the well the interaction stronger the  What can the the position of the PE well on the x axis tell you? A. The distance between the atom centers at their most stable point B. How much energy would be needed to overcome the interaction C. Nothing 47 < 7 Which has the longer internuclear distance? large V A) Helium atoms B) Xenon atoms Notice how the bigger atoms have the longer internuclear distance (Atom “sizes” are often listed as Van der Waals radii, which are defined as Van der Waals radius ½ the distance between the atoms at the potential minimum). ↑ a stable point of bottom & 7 7 Internuclear Distance  Activity Draw a graph showing how the potential energy of a two helium atom system changes as the He atoms approach each other. Use a solid line for He. On the same set of axes, use a dashed line (------) to show how the potential energy changes when two Xe atoms approach each other. Explain how and why the two curves differ from each other.  He Xe PE ↑S & - Deeper b/c b,c it the forms electron a stronger clouds are LDF He j larger t and so fas far the right centers is longer the distance Down are more electrons E Stronger LDF bic there in the cloud of XE there are larger 8 charges force and stranger LDE which means stronger Which substance has the larger atomic radius? A. A D/C B is farther 2 right to the B. B C. Not enough information D. Don’t know How do you know? B A PE decreases with the increase in radius Which is the substance with the higher boiling point? deeper wells meaning A. A L stronger more heat bonds to + break needs B. B C. Not enough information D. Don’t know Explain why. B A Without looking up the values, which would you - predict to have a higher boiling point: neon (Ne) or argon (Ar) Office Bring to Hours ! (for Feedback) What is your claim? What evidence (data or scientific principle) will you use to explain this? What is the reasoning that links your claim and evidence?  Formation of Covalent Bonds When two H atoms approach – they are attracted much more strongly than two He atoms. They form a covalent bond. (We will worry about why in chapter 3) What happens when two hydrogen atoms approach? M clouds election M biend much toegemeaum What happens when we remove energy? ↑ bund systemofn.caraient and H The two H atoms have formed a NEW chemical species – a hydrogen molecule (___). Hz It has different chemical and physical properties than hydrogen atoms (__). H  Hydrogen atoms (H) interact to form hydrogen molecules (H2) 2 As we will see the properties of H2 (molecules) are very S L 2 # nuclei molecule for different than H (atoms). – Sometimes it can be confusing because we call them both hydrogen. T oval + 2 dots H2 & Under normal circumstances molecule 6 hydrogen exists as H2& # Na Oz Fy , , , Cly Bry Is z , , , · Atom diatomic < one snown nucleus ! molecules. (7) total Other diatomic molecules H atom include: O2 N2 F2 Cl2 Br2 2 272 2 I2 2 Nuclei of Hiumuch further Hydrogen than Bonds and IMFs: A Range of Interactions Look at the differences in the PE wells for He and H LDF atoms is depth deeper for 2 Hydrogen Which type of atoms interaction is stronger? W A. Covalent bond covalent B. LDF C. Equal strength D. Don’t know A Range of Interactions Between Atoms between Y Intermolecular Forces (IMFs) include London Dispersion Forces and other van der Waals interactions that we haven’t talked about yet. – They are relatively weak. – All IMFs occur between neutral molecules or utral molecules or atoms. p. -.. Bonds are more permanent. covalent bund (within) LDF (between) – They are stronger and harder to break. er to break DE I – Bonds occur within molecules. ~ /MFSs and bonds are NOT the same thing !  IMFs and bonds are NOT the same thing. What happens when helium is heated? What happens when hydrogen is heated? - after collision energy placed in system + Separates in > at ons  waremich ↳ V Why do you think it takes a temperature of 6000K to break the interaction between two H atoms – but only 14K to break the interaction between two He atoms?  Hydrogen melts at 10K and boils at around 20K, but the hydrogen molecules do not form hydrogen atoms until the temperature reaches over 6000K (as shown on page 8 of the simulation). Draw a picture of what hydrogen looks like at: 5K Indicate and label any bonds and/or interactions 15 K that are present at each 30 K temperature. Above 6000 K  molecules melting eiquid solid 10k overcoming zu = mp yp = 20k someF contact covalent bonds within V W Faximdype covent - - bon in : : LDF...... So gas phase 5K No LDFS meltinglok d point atoms 15K of my posit ok No LDFs no covalent bonds i covalent renor overcoming ~ Es. a e remaining - Chemicale presen & #(g) bescent Helg) 30K >6000K ↓ transferred collision  is > helium - great nube At 5 K, what holds the A) Gravity nuclei together within B) LDFs an H2 molecule? S C) Covalent bond D) I don’t know At 5 K, why do molecules of H2 stick to other molecules of H2? B a breaking Ithe temperature? What happens as we increase Which processes are phase changes and which are chemical reactions? ↑ breakingand covalent  Which statement about the breaking of a single chemical bond is true? wing * A. B. Energy is released. energet Energy is absorbed. swY C. Energy is released or absorbed depending on the polarity of the bond being broken. D. Energy is released or absorbed depending on the strength of the bond being broken.  Which statement about the forming of a single chemical bond is true? is ↳reverse A. Energy is released. B. Energy is absorbed. C. Energy is released or absorbed depending on the polarity of the bond being broken. D. Energy is released or absorbed depending on the strength of the bond being broken.  Breaking bonds requires an input of energy (to the system). The energy is mo transferred into the system upon collision with other molecules. Forming bonds releases energy (from the system). The energy is transferred out of the system upon collision with other molecules. Breaking bonds requires an input of energy (to the system). The energy is transferred into the system upon collision with other molecules. Forming bonds releases energy (from the system). The energy is transferred out of the system upon collision with other molecules.