CEM 141 Exam 1

Is this a scientific question: What temperature will my coffee be if I add coffee to it?
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Is this a scientific question: What temperature will my coffee be if I add coffee to it?
Yes, it is a scientific question because it is measurable and testable.
Is this a scientific question: Do dragons have wings?
No, this is not a scientific question because it is not measurable or testable.
Scientific Questions
They can be answered by:
doing experiments
making observations
taking measurements
Scientific questions have to be done in a __________way. (If someone else can't ______ it then it is not science!)
Replicable, repeat
Every claim must be supported with __________.
Evidence!
For example, "What evidence do we have for the existence of atoms?" and "What is the evidence that there is an attractive force between objects with mass?"
Evidence
It comes from your experiment and supports your claim.
Is this example a claim or is it considered evidence? If I add cold milk to hot coffee the coffee will cool down.
This is a claim.
Is this example a claim or is it considered evidence? The temperature of the coffee/milk mixture was 10*C lower than the temperature of the coffee alone.
This is evidence of a claim.
Scientific Model
It can be a drawing, graph, diagram, or an equation (physical or mental).
Why do we use scientific models?
We use models to help us make sense by
1. predicting what will happen. (they make testable, quantifiable predictions)
2. explaining how something happens
Scientific Explanationsscientific explanations and scientific theories help us explain the why part of scientific questions.What are the three parts to 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 (answers the question asked) 2. evidence: the data or scientific principle you are using to support your claim 3. reasoning: the connection between your claim and evidence Remember C.E.R.Example of a scientific explanation using C.E.R.Claim: Coffee cools down when milk is added to it. Evidence: because the temperature of the coffee/milk mixture is lower than that of the coffee alone. Reasoning: the coffee molecules (with higher kinetic energy) collide with the milk molecules (with lower kinetic energy) and transfer energy. Because the coffee molecules now have less kinetic energy, their temperature is lower.What is a scientific theory?-The best available explanation of the existing evidence/data/observations -explains how and/or why -makes testable predictions -is falsifiable (like it can be proven false by experiments and data) -may change over time as new evidence becomes availableWhat is the difference between a Law and a Theory?A law describes the phenomenon (it tells you what). A theory explains the phenomenon (it tells you why).Which of the following is a: 1. Fact 2. Law 3. Hypothesis 4. Theory 5. QuestionA. Special Relativity (time and space are not absolute but are relative to each other) THEORY B. The force of attraction between masses is proportional to the product of the masses, and inversely proportional to the square of the distance between them. LAW C. An atom of hydrogen has one proton. FACT D. If we add reagent X to a reaction it will go faster. HYPOTHESIS E. What will happen if we add X to the reaction? QUESTIONAtoms"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."Which has atoms in it? Heat, Cells, Air, Gold 1. All of them 2. Cells and Gold 3. Cells, Air and Gold Only GoldC. Cells, Air and Gold. (Heat is energy so it has no atoms because it is NOT matter, and only matter has atoms)Which is biggest? A. An atom B. A molecule C. A cell D. It dependsC. A Cell and D. It depends because it depends on what you mean by "biggest" (note: an atom is not always smaller than a molecule)How big is an atom? 1. about 0.1 cm (0.1 x 10^-2m) 2. about 0.1 mm (0.1 x 10^-3m) 3. about 0.1 um (0.1 x 10^-6m) 4. about 0.1 nm (0.1 x 10^-9m) 5. about 0.1 pm (0.1 x 10^-12m)4. about 0.1 nm (0.1 x 10^-9m)Scientists claim that atoms exist. What is our evidence of this?1. scientific methods and experiments to help us visualize atoms 2. provide evidence to support the claim that atoms existAtomic Force Microscopy (AFM)-A technique that maps the three dimensional topography of a object using van der Waals forces between the object and a probe. -It helps us determine where electrons are and create a model from it.Scanning Tunneling Microscopy (STM)microscope that measures electrons that leak or "tunnel" from the surface of the specimen. It provides images at the atomic level.Where did the original idea of atom come from? And was this a scientific theory? (Based on experiments, data and evidence)The Greeks, and their ideas did not constitute a scientific theory. They had no data or evidence, their ideas emerged purely from philosophy.Development of Atomic Theory-The Greeks: this was the earliest atomic theory that was based on philosophy, not experimental evidence. -They believed that the movement of specks of duct in the sunlight led to the conclusion that atoms were in constant motion with nothing, or a "void" between them. -"Atomos" means not to be cut Elements: Earth, fire, air and waterDevelopment of Atomic TheoryThe random motion of atoms and particles that the Greeks developed ideas regarding were later called Brownian motion.If "earth has atoms that were cubic, what shape would you ascribe to the Greek element "water"?a) They could observe water as flowing so they thought the shape of the atoms must be smooth on the outside/surface so the atoms could flow and move with one another.The Greeks believed that the ________ of atoms determined their properties.ShapeIf "earth has atoms that were cubic, what shape would you ascribe to the Greek element "iron"?b) Iron was a solid that did not flow so they thought the atoms must be sticky on the outside/surface with sharp jagged points to hold them together.An _______is the smallest unit of an element.AtomWhy are the atoms of different elements different?They have different properties and this is determined by the number of protons.How many elements are there?118 total (because some are "manmade" ) but there are 91/98 elements that are naturally occurring.What are the following/what do they represent for elements on the periodic table? 1. He 2. The two above the He 3. The number below He (4.003)1. He is the chemical symbol for the element, Helium. 2. The 2 represents the atomic number of Helium. Every element has a different atomic number and this tells you the # of protons in the nucleus. 3. The 4.003 below the chemical symbol for Helium represents the atomic mass of the element. It is the average mass of one atom of that element.How would you explain the difference between an atom and an element using gold?Gold atoms: are individual nanoscale entities that are too small to see with the eye. Elemental gold (also called gold ore): are a collection of gold atoms that are considered a macroscopic sample. Overall, atoms and elements have very different properties.An atom of an elementThis could be a representation of many different atoms, like oxygen (O), nitrogen(N), etc.A molecule of an elementcombination of two or more of the same atoms (Would be represented as H2). Important to remember that an element is made up of the same kind of atom! And it's a molecule because a molecule is a collection of atoms so more than one atom makes it a molecule (:A molecule of a compoundA compound is made up of more than one type of atom, and more types of elements.An atom of a compoundThat's impossible!Dalton's Atomic Theory1) elements are composed of small indivisible, indestructible particles called atoms 2) atoms of an element are identical and have the same mass and properties 3) atoms of a given element are different from atoms of other elements 4) compounds are formed by combinations of atoms of two or more elements 5) chemical reactions are due to the rearrangements of atoms; atoms (matter) are neither created nor destroyed during a reaction.To change a theory, you would need what?New evidence is needed to change a theory.Are all the tenets (the 5 components) of Dalton's theory still considered to be true today?1) elements are composed of small indivisible, indestructible particles called atoms. NO, we have evidence of subatomic particles. 2) atoms of an element are identical and have the same mass and properties. NO, the existence of isotopes proves this. 3) atoms of a given element are different from atoms of other elements. YES, they have a different # of protons and thus different properties. 4) compounds are formed by combinations of atoms of two or more elements. YES, this is the definition of a compound. 5) chemical reactions are due to the rearrangements of atoms; atoms (matter) are neither created nor destroyed during a reaction. YES, this is true for chemical reactions (but not nuclear reactions).Which subatomic particle was discovered first? 1. Proton 2. Electron 3. Neutron2. Electron This is because they are on the outer edge of the atom and they have a charge.Who discovered the electron and by what means?JJ Thomson, by the cathode ray experimentWhat is the cathode ray experiment?Cathode ray tubeIt is a glass tube that consisted of two electrodes (cathode (+) and anode (-)) under very low pressure. When a high voltage is applied, the cathode emits "particles" that move toward the anode.Evidence of the discovery of the electronHow the cathode ray tube experiment was conducted (in the picture).What were the observations from JJ Thomson's experiments?-Particles emerged from the cathode and moved to the anode. -These particles were deflected by electrical fields in a direction that indicated they were negatively charged. -The metal that the cathode was made of did not affect the behavior of the ray. The composition of the ray appeared to be independent of the element that it came from. (Chapter 1- Slide 56)What is the evidence from Thomson's experiment that all atoms contain electrons? 1. the particles were attracted to the + electrode 2. the particles were deflected by magnetic fields 3. the particles were deflected by electrical fields 4. the particles were identical regardless of the metal used for the cathode (where they were emitted from)4. the particles were identical regardless of the metal used for the cathode (where they were emitted from) (Note: all the answers are true, but this is the answer with specific evidence that supports the claim)Thomson's "Plum Pudding" Model of the atomAtoms contain electrons "embedded" in a positively charged blob. (Atoms themselves are neutral, so the rest of the atom must be positively charged)Rutherford's experimentThe experiment that proved the nucleus must be positively charged (as alpha particles were scattered/deflected by a piece of gold foil)What is an alpha particle?It has 2 protons and 2 neutrons. It is the nucleus of a helium atom.Nuclear AtomMost alpha particles go straight through, but Rutherford said that most, mass is concentrated in small space (we know this as a nucleus)Plum Pudding AtomIf the atom has like a plum pudding, all the alpha particles should go straight through, but this is not what happens (as we now know)Rutherford's gold foil experiment showed:-that am atom is mostly empty space -small dense positive nucleus in the center of the atomRutherford's Planetary Model (Nuclear model of the atom)In the planetary model of the atom, the electron should emit energy and spirally fall on the nucleus (the orbiting electron will lose energy and eventually implode)Neutronsthe particles of the nucleus that have no charge. They reside in the nucleus and are slightly heavier than protons.When were neutrons discovered and why were they harder to detect?They were discovered in 1932 and are harder to detect because neutrons are neutral in charge- so they are not manipulated with electric and magnetic fields.What is the most recent model of the atom that are we are using for now?-electrically neutral -very small nucleus (~2 x 10^-15m) contains 1. protons (+1 charge, 1 amu) 2. neutrons (0 charge, 1 amu) -"Cloud" of electrons takes up most space (~20-200 x 10^-12m) 1. electrons (-1 charge, ~1/1800 amu)Reflection Questions for studying:- Why don't the protons within a nucleus repel one another -Why don't the electrons and protons come together within the nucleus? (Why don't atoms collapse?) -Do the electrons within an atom repel each other?Atom InteractionsWe can explain how atoms interact using the idea that opposite charges attract and like charges repel. (Coulomb's Law)What is an attraction?An interaction is a force (what is happening between/within them), and the basic definition of a force is a push or a pull.What are the 4 fundamental forces?1) Gravity 2) Electromagnetic/ Elecrostatic 3) Strong 4) WeakGravityIs responsible for attraction between objects that have mass. (We have the most experience with this force)Electromagnetic/ElectrostaticResponsible for attraction/repulsion between objects that have electric charge. (This is the force that we need to understand)StrongShort range interaction that occurs between objects made of quarks (like protons and neutrons, which are held together in the nucleus despite electrical repulsions between protons)Here is Matt. He has a ball thrown 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 ca) gravitationalWhat happens to the gravitational force of attraction as the mass of the interacting objects increases?The force increases because it pulls it down faster/with more force.What happens to the gravitational force of attraction as the distance between the objects increases?The force decreases because there is not as much force to act upon.Newton's Law of Universal GravitationThe law that says every object in the universe attracts every other object, and that the force is affected by mass and distance: the greater the mass of an object, the greater the attraction; the farther apart the objects, the weaker the attraction. It is modeled by this equation:Gravitational Forces are Mediated by ______________ _______________.Gravitational FieldsGravitational Forces-Objects with mass are sources of gravitational fields and are affected by the gravitational fields of all other objects with mass. -Gravitational forces require two or more objects (and those objects need to have mass!) -Gravitational forces are always attractive.The electromagnetic force is mediated by ________ and _________ fields.electric, magneticElectromagnetic Force-A force associated with charged particles, which has two aspects, electric force and magnetic force. -Electromagnetic forces act at a distance -The electromagnetic force is much stronger then gravity and can be both attractive and repulsiveElectrostatic ForceThe force between electrically charged objects (like charges repel and opposite charges attract each other). We will only consider electric fields and forces between charged particles right now- this is a special case of the electromagnetic force and is called the electrostatic force.If two objects have the same charge what happens? 1. they repel each other 2. they attract each other 3. nothing happens1. they repel each otherIf two objects have opposite charges what happens? 1. they repel each other 2. they attract each other 3. nothing happens2. they attract each other_______ charges attract and ______ charges repel.unlike, likeThe force between charges can be modeled by using ________.Coulomb's lawCoulomb's Lawelectric force between charged objects depends on the distance between the objects and the magnitude of the charges. F=K q₁*q₂/r², magnitude of force between two charges.Both the gravitational attraction between masses and the electrostatic attraction between charged particles follow an __________________, but the electromagnetic (electrostatic) force is much stronger (than gravity) and can be attractive and repulsive.inverse square lawGravitational forces are _______ to be detected at the atomic/molecular level.too weakHere is Mariam. She has a ball in her hand. What forces are acting on the ball? a) gravitational b) electrostatic c) both a and b d) there are no forces because the ball is not movingc) both a and bThe electrostatic force stops us from falling through the Earth because (think about what makes us "hover" over chairs)at rest there are always two forces!If something is not moving, either there is _____ force acting upon it or the forces acting on it are _____ and ______.no, equal, oppositeWe can stand on the earth because the force of gravity is ______ and _______ to the electromagnetic force.equal and oppositeWhat is energy?We don't actually know- but the definitions are often circular. This is what we do know: -any change in matter is accompanied by a change in energy -changes in energy are caused by changes in forces -energy is conserved (depends on the system defined though) -Units SI- Joule (kg m^2s^-2) 1 calorie = 4.184 JSystems->To study energy changes, we must define what we are studying -system: part of the universe you are looking at -surroundings: everything else in the universe ->Can monitor energy changes between system and surroundings -> Energy is never lost- it can be transferred or transformed (First law of thermodynamics)There are two types of energyKinetic and Potential (also electromagnetic-but that is a special case) -all other forms of energy can be related to these two at the molecular levelKinetic Energy-the energy that is associated with motion -Kinetic energy = 1/2mv^2 m is mass v is velocity (for speed)Here is Betoul. The ball is falling down. As the ball moves toward the ground what happens to the kinetic energy? a) increase b) decrease c) stays the samea) increasePotential 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 that is 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) -When the position of two objects in a field changes, so does the potential energy of the system.Here is Betoul again, and 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) decrease c) stays the sameb) decreaseHere is Betoul again. The ball is falling down. What causes the potential energy to decrease? a) the kinetic energy increasing b ) the change in position between the ball and earth in the gravitational field c) the weight of the ballb ) the change in position between the ball and earth in the gravitational fieldHere is Betoul again. The ball is falling down. What causes the ball to fall down? a) the potential energy of the system is decreasing b) the kinetic energy is increasing c) the gravitational interaction between the earth and the ballc) the gravitational interaction between the earth and the ballHere 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 c) stays the samec) stays the sameEnergy can be _______ (from one object to another) and ______ (like from potential to kinetic energy).Transferred, transformedWhat do all of these forces and energy have to do with chemistry?Atoms are made up of charged particles, and therefore, the electrostatic force is important. We can understand atomic interactions in terms of Coulombic attractions and repulsions.There must be some mechanism by which atoms stick together to make ______.to make molecules to make solids from liquids (freezing) and to make liquids from gases (condensation).The temperature at which a solid changes to a liquid (of the same chemical identity) is a) the melting point b) the freezing point c) the boiling pointa) the melting point____________ do not react with anything. (these are a part of group 8A on the periodic table).Helium (and all the noble gases)Helium has a melting point of 0.95k (-272.2*C) and has a boiling point of 4.5k (-268.5*C). What does this mean?If it has a melting point it can exist as a solid and a liquid. If it has a boiling point then it can exist as a liquid and a gas. So this means that something must make the atoms stick together.How do we represent the atoms as a solid, a liquid, and a gas?(Ex. Helium-He) As a solid, the atoms are very organized and touching. As a liquid the atoms are less organized but are still touching. As a gas though, there is no organization within the atoms and they are not touching, but can collide and bump into each other.What are the physical states of matter?1. Solid: -molecules are closely packed in definite arrangements -volume and shape independent of container -incompressible 2. Liquid: -molecules move in relation to one another -volume independent of container -no fixed shape -incompressible 3. Gas: -molecules far apart, move with high speed, collide -no fixed volume or shape -compressible1. Solid to liquid= ______ 2. Liquid to gas=_______ 3. Liquid to solid=________ 4. Gas to liquid=_________ 5. Gas to solid=________ 6. Solid to gas=________1. melt 2. vaporize 3. freeze 4. condense 5. deposit 6. sublimeLondon Dispersion ForcesThe intermolecular attractions resulting from the constant motion of electrons and the creation of instantaneous dipoles. -caused by fluctuations of electron density in the molecule (or atom) -adjacent molecule-gets induced dipole -present between ALL molecules (neutral species) Note: LDFs do not exist in gasses!!!London Dispersion Forces (LDFs)instantaneous induced dipole ----> induced dipole interactions The separation of charge = dipoleHow many Helium (He) atoms must be present for LDFs to exist? a) none b) one c) two or morec) two or more Note: LDFs exist between ALL neutral atoms and molecules in the solid and liquid statesAn _______ dipole on one helium atom can induce an _______ dipole on neighboring atom, which can then ______ one another.instantaneous, instantaneous, attractWhat happens when two atoms of Neon (Ne) approach each other? As these two Ne atoms come together, what happens to the electrostatic force? a)increases b)decreases c)stays the samea) increases because the distance is increasing as they come together.The _________ Coulombic interaction causes the atoms to approach, but is they get too close, the electron clouds overlap and the _______ force becomes dominant.attractive, repulsiveAs the atoms approach each other the potential energy _____. As the atoms move very close together the potential energy ______.decreases - because there is not as much force between them Increases - because the electron clouds overlap and the repulsion force becomes dominant (there is more force to push them away from each other at this point)What does the potential energy curve look like for the internuclear distance between atoms?On the potential energy curve, as the atoms move toward each other, which force is the strongest? a) electrostatic attraction b) electrostatic repulsion c) gravitation d) ES attraction = ES repulsiona) electrostatic attractionOn the potential energy curve at the potential minimum (well), which force is the strongest? a) electrostatic attraction b) electrostatic repulsion c) gravitation d) ES attraction = ES repulsiond) ES attraction = ES repulsionOn the potential energy curve, as the atoms move even closer, which force is the strongest? a) electrostatic attraction b) electrostatic repulsion c) gravitation d) ES attraction = ES repulsionb) electrostatic repulsionAs the atoms move together, the potential energy ____ because they are moving with the attractive force .decreasesAt the potential energy minimum, the system is ________. The attractive force equals the repulsive forces.most stableAs the atoms move even closer, the potential energy ______, because they are moving against the repulsive force. When they get too close together, the repulsive force becomes strong enough to push the atoms apart.increasesWhat happens as two helium atoms approach each other?Kinetic energy as well as potential energy changed but total energy did not change.What is different about these three sets of atoms? 1. 200 pm distance between nucleus 2. 120 pm distance between nucleus 3. 150 pm distance between nucleus1. The atoms are the furthest apart on the potential energy curve 2. The electron clouds of the atoms overlap on the potential energy curve 3. The atoms are the perfect distance from each other - the "minimum" where London Dispersion Forces (LDFs) can occurAs helium atoms initially approach what happens to: 1. The total energy 2. the kinetic energy 3. the potential energy1. stays the same, because this is an isolated system (the total energy is trapped in the system - does not gain or lose energy) 2. increases, because the atoms are attracted to each other 3. decreases, because the atoms are moving "with" the forceAs helium atoms get very close (overlapping electron clouds) what happens to: 1. The total energy 2. the kinetic energy 3. the potential energy1. stays the same, because it is an isolated system 2. decreases, because once overlapped they have to slow to be able to begin to move the opposite way 3. increases, because the atoms are moving against the repulsive forceWhy don't Helium (He) atoms stay in this potential minimum?They have to collide for energy to transfer and they had too much energy so its just going to roll back up the other side (if thinking about it like a ball)One the Helium atoms are stuck in the potential well, what prevents them from flying apart (why do they stick together)?London dispersion forces (LDFs)What can the position of the potential energy (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 over come the interaction c) nothinga) the distance between the atom centers at their most stable pointWhat can the depth of the potential energy (PE) well tell you? a) the distance between the atom centers at their most stable point b) how much energy would be needed to over come the interaction c) nothingb) how much energy would be needed to over come the interactionWhat would we have to do to break the LDFs between the Helium (He) atoms (and get them out of the potential well)?Add energyIn the "real world", how would energy normally be removed (or added) from the two atoms?Change temperatureWhen you change the temperature of the system, where does the energy come from/go?By atoms colliding with atoms not in the systemWhat happens when you add thermal energy to the helium atoms (raise the temperature)?Kinetic energy is transferred to the atoms upon collision, causing them to move faster (because they have more kinetic energy) When a collision transfers enough kinetic energy to the two helium (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 (1/2mv^2) of all the atoms -temperature, T, is directly related to average kinetic energy (1/2mv^2) of the atomsHow do the Helium (He) atoms (in the system) "know" that the temperature is rising? (or increasing) a a) the air is warmer and warms the He atoms b) the energy is transferred from other atoms that have collided with the walls of the container (that were directly heated) c) the atoms move faster when the temperature increases d) the heat atoms bump into the He atomsb) the energy is transferred from other atoms that have collided with the walls of the container (that were directly heated) (The energy is transferred upon collision within atoms in the surroundings- the atoms had gotten the energy by colliding with the walls of the container which were at a higher temperature)Which statement about the breaking of an attractive force (LDFs) between two atoms is true? a) energy is released b) energy is absorbed c) energy is released or absorbed depending on the polarity d) energy is released or absorbed depending on the strength of the interaction being brokenb) energy is absorbedWhich has more electrons: He or Xe?Xe, because it has the bigger atomic number (according to the periodic table). 54>2 He has 2 electrons, Xe has 54, so it has a much bigger electron cloud (electrons are much farther from the nucleus) and the electron cloud in Xe is "floppier" so it is more easily distorted.Compared to He, the London Dispersion Forces between Xe atoms are expected to be _______.StrongerLondon Dispersion Forces-increase with size of atom/molecule (number of interactions) -increase with surface area -part of a range of intermolecular forces (between particles) - have to have at least 2 particlesWhich do you think would have the higher melting and/or boiling point? why? a) He b) Xe c) they would be the sameb) XeHelium (He) has a melting point of 1K, and Xenon (Xe) has a melting point of 161K. Was your prediction correct?Yes, because the interaction between those two xenon atoms is stronger and it takes more energy to overcome that stronger interaction between the xenon atomsWhat can the depth of the potential energy well tell you?how much energy would be needed to overcome the interaction it also tells you something about how strong the interaction between the atoms is and how much energy would be needed to get the atoms out of the well.what can the distance of the potential energy well on the x-axis tell you?the distance between the atom centers at their most stable pointThe _________ distance of the well tells you how far away from each other the atom centers are, at the most stable pointinternuclearWhich has the longer internuclear distance? a) Helium atoms b) Xenon atomsb) Xenon atomsBigger atoms have the longer internuclear distanceAtom "sizes" are often listed as Van Der Waals radii, which are defined as 1/2 the distance between the atoms at the potential minimumWhich substance has the larger atomic radius? a) a b) b c) not enough infob) bHe vs Xe on the potential energy curveXe = higher melting/boiling point because the well is lower on the PE curveWhich is the substance with the higher boiling point? (stronger LDF) a) a b) b c) not enough infoa) a because the position of the minimum- needs more energyWhich is the substance boils at a lower temperature? a) a b) b c) not enough infoa) aFormation of covalent bondsWhen two H atoms approach - they are attracted much more strongly than two He atoms -They form a covalent bondThe two H atoms have formed a NEW chemical species- a hydrogen ________.molecule (H2) It has different chemical and physical properties than hydrogen atoms (H)Hydrogen atoms (H) interact to form hydrogen molecules (H2)-as we will see the properties of H2 molecules are very different than H atoms -under normal circumstances hydrogen exists as H2 molecules -other diatomic molecules include: O2, N2, F2, Cl2, Br2, I2 -Note!! Noble gases like Helium (He) exist as discrete atomsIntermolecular forces (IMFs) include:London dispersion forces (LDFs) and other van der Waals interactions what we haven't talked about yet -they are relatively weak -all IMFs occur between neutral atoms or molecules________ are more permanentBonds -they are stronger and harder to break then IMFs -bonds occur within molecules Bonds and intermolecular forces (IMFs) are NOT the same thingWhat happens when helium is heated?Energy is added to get out of the minimumWhy do you think it takes a temperature of 6000K to break the interaction between two Hydrogen atoms- but only 14K to break the interaction between two He atoms?The covalent bond in H is stonier than the LDF in HeHydrogen melts at 10K and boils at around 20K, but the Hydrogen molecules do not form hydrogen atoms until the temperature reaches over 6000K.This is a pic of what hydrogen looks like at 5, 15, 30 and above 6000KAt 5K, what holds the nuclei together within an H2 molecule?Covalent bondAt 5K, why do molecules of H2 stick to other molecules of H2?London dispersion forcesWhich statement about the breaking of a single chemical bond is true?Energy is absorbedWhich statement about the forming of a single chemical bond is true?Energy is releasedBreaking bondsrequires an input of energy (to the system). The energy is transferred into the system upon collision with other moleculesForming bondsreleases energy (from the system). The energy is transferred out of the system upon collision with other molecules.