What is the universe made of…?

1. What is the universe made of…? • Everything in the universe falls into two categories: matter, and light! • Matter, as we have seen, is made of atoms, and atoms are made of protons, neutrons, and electrons! • What is light, though? • Light is also called energy, which • is also known as electromagnetic radiation! • If you can touch it, it is matter! • Otherwise, it is energy, or light!

2. Light travels in waves….

3. There are three things we can measure about a light wave - Its speed, its frequency, and its wavelength! Frequency,  – number of waves that pass through a particular Point in one second. Units: waves/second, also known as Hertz (Hz) Wavelength, l - distance between two consecutive waves - Units: meters, mm, cm, nm - any distance units! Speed, c - the number of meters a light wave can travel in one second. Units: meters per second (m/s) A or B…..? A Which wave is faster….? B

4. They travel at the same speed! • They are both light waves, which means that they travel at……. • The speed of light! • The speed of light, or c, is equal to 3.00 x 108 m/s • This is 300 million meters in a second! • That means a light wave can travel around the Earth 10 times in a second! • How do all light waves travel at the same speed?

5. Light and Electromagnetic Radiation • Electromagnetic radiation, aka energy, aka light, includes visible, IR, UV, gamma rays, X-rays, TV waves, radio waves, and all other forms of light • Our eyes are only equipped to see “visible” light, and all other types of light or energy are invisible to us. Our bodies are sensitive to other types of light or energy, though. Which other types of energy can our bodies sense? • Pit vipers can see the infrared “color” which is radiant heat, a color we cannot see. • Visible white light is a mixture of all colors in the rainbow • Speed of light (c) - in a vacuum is constant for all types - 3.00 x 108 m/s • C = v l

6. High Energy Low Energy

7. Light or Electromagnetic Radiation or Energy • Colors of visible light waves depend on their wavelength or frequency • The different kinds of visible light can be arranged by wavelength into an electromagnetic spectrum • Different colors of visible light have different energies, where violet light has more energy than red light • Visible light ranges from 400 nm – 800 nm • “black light” – which is really near UV light, causes certain objects to fluoresce or “glow” • Fluorescence –UV (non-visible) light is absorbed by electrons in atoms and then emitted at longer visible wavelengths, such as violet or purple visible light 400 nm 800 nm

9. High Energy Low Energy Electromagnetic spectrum

10. Small wavelengths High Frequency (Highest Energy) Large wavelengths Low Frequency (Lowest Energy) The Electromagnetic Spectrum

12. So how do matter and energy relate to one another…? • We know that matter and energy have the ability to interact with one another…. • Matter can absorb energy….. • Examples…? • Matter can give off energy…. • Examples…? • And until recently, most people thought that matter absorbed and released energy continuously…. • What does that mean…?

13. Think about how things are heated…. • When solids are heated, they emit light of all different energies • A warm solid at 7500C will glow red, and a hot solid at 10000C will glow blue…this makes sense, right? • At extremely high temperatures, there were some energies not being emitted at all…. • Certain energies in between weren’t emitted as well…. • This didn’t make sense…. • Have you ever seen a pot being heated…? • It gradually heats up…. • And gradually cools down…! • The energy change is continuous! • It emits all energies, all along the way!

14. A scientist named Max Planck studied this intensely! • Max Planck was told by his professor not to study physics, as all the famous discoveries had been made! • He then went on to win the Nobel Prize in 1918! • Planck’s assumption: vibrating atoms in a heated object gave rise to emitted energy; atoms and molecules could give off or absorb energy only in definite amounts, called quanta - not continuously. • He said that energy was not absorbed or given off continuously, but in definite amounts….or jumps of energy….. • This is why, he said, only certain types of energy were seen. • This is called QUANTUM THEORY! • Is this what you observe around you? • This would be the same as driving a car, but only being able to drive at 10 mph, and then 20 mph, and then 30 mph, but never in between! • Does a pot on your stove heat up or cool down like this? Doesn’t it heat up gradually and cool down gradually? • How can this be true? • Other scientists thought Max Planck was crazy!

15. Max Planck nearly lost his reputation on Quantum Theory… • It is obvious that things absorb and release energy continuously…. • Think of fires, pots, pans, human bodies, water, etc. • Experimentally, the quantum assumption part of his theory was shaky…. • Even Max Planck tried to eliminate it from his theory! • A scientist came along to help him out and save the day by proving him right! • Albert Einstein! • He would win his first Nobel Prize for an experiment called the… • Photoelectric Effect!

16. Trying to increase the energy by increasing the amount of red light each time Photoelectric Effect Changing the color of the light electrons emitted ? electrons emitted ? Sodium Sodium Red Light Red Light No No Blue Light No No No Violet Light e- Yes, with high speed e- No e- No electrons were emitteduntil the frequency of the light was above a minimum frequency, at which point all electrons were emitted from the surface! That minimum frequency is different for every substance in the universe!

17. Photoelectric Effect • If energy absorption was continuous, what should have happened when the amount of red light was increased gradually….? • Gradually, more and more electrons should have left! • But nothing happened when the red light amount was increased! • This told Einstein that energy absorption was not gradual or continuous, but occurred in definite amounts, or quanta • The real question was this - HOW DID A LIGHT WAVE MOVE MATTER? • An electron is matter, right? • Have you ever had a light wave move you? You are made of matter, right? Violet

18. Photoelectric Effect • Many scientists laughed at Einstein! They said that his idea was ridiculous! It was impossible for light to move an electron! Or any matter! • So Einstein said….. • LIGHT IS MADE OF MATTER! • Each light wave contains tiny little particles called photons! • Not protons, but photons! • Increasing the amount of waves is simply increasing the numberof photons, but its NOT increasing the energy of each wave! • However, if the energy of these “photons” is related to their frequency, this would explain why higher frequency light waves canknock the electrons out of atoms, but low frequency light waves can’t… • High frequency light waves have more photons, that have more energy, to move matter!

19. “Photon” Before Collision After Collision Photoelectric Effect • The only way to move matter is WITH matter! • Why, then, do light waves not move your electrons or atoms? • They do! • Remember, every matter in the universe is sensitive to photons of a particular light! • What kind of light waves can do damage to your atoms? • UV waves, X Rays, or Gamma Waves can remove electrons from your DNA and cause permanent damage to your cells! Visible waves do not have enough photons to cause damage! • In this atomic picture, the energy of the photon must overcome the binding energy of the electron to the nucleus. • If the energy of the photon exceeds the binding energy, theelectron is given off!

20. What does a discussion about light have to do with the structure of the atom? • A scientist named Neils Bohr, a great friend of Einstein, noticed something peculiar about Hydrogen • A hydrogen atom consists of 1 electron orbiting 1 proton…. • As we know, when substances absorb energy, they can release that energy as well! • Atoms can release all kinds of different energy - visible light, infrared light (heat), ultraviolet light, etc. • Think about light bulbs, neon lights, fluorescent lights, heat lamps - these are all examples of how atoms can give off energy! • What part of the atom did Bohr now know was responsible for energy absorption, thanks to his good friend Einstein? • …..The electron! • With one electron, how many different types of energy or colors of light do you think hydrogen can give off….?

21. …. Only one color of light! • Bohr studied a simple experiment, though - one we are going to look at right now! • Bohr excited hydrogen atoms with high voltage electricity • The hydrogen atoms absorbed the electrical energy, and emitted violet light • The violet light was actually FOUR DIFFERENT COLORS OF LIGHT, as viewed through a prism • Each color represents a different wavelength of light!

22. HOW IS THIS POSSIBLE…? • It doesn’t make sense that one electron can be responsible for four different colors of light! • Hydrogen, with only one electron, should be emitting only one type of energy! • Bohr came up with an explanation for this…. • It involved changing the current accepted model of the atom!

23. Bohr theorized a new model for the atom… • Bohr suggested that it was possible for electrons to move to many locations or “energy levels” within the atom! • This is why he was seeing a line spectra with hydrogen! • Bohr used line spectra to explain electron structure in atoms. • The four lines represented something about the one electron in hydrogen moving! • What do you think it represented…? • The electron was moving to more than one location in the atom! • In Bohr’s Model of the atom, electrons orbit the nucleus like planets orbit the sun. • Different distances from the nucleus represent different energies • Electrons can only exist at these specific energy levels, and have specific energies - they can never be in between! • This supported Planck’s and Einstein’s “Quantum Theory”!

24. So how did one electron give off four different colors of light…? • Electrons can absorb a photon of light when it collides with the electron – it then moves to a higher energy level, based on the amount of light with which it was hit • Electrons can fall to lower energy levels by emitting photons of light equal to the difference between the energy level they started at and the one they end up at • Ground state – an electron in the lowest energy level possible • Excited state - by absorbing specific energy from light, an electron can move to a higher energy level, away from the positive pull of the nucleus • This excited state is unstable, and the electron wants to go back down to its normal ground state • When the electron falls, it releases light as it falls back down to the ground state • Why, then, does hydrogen give off four distinct colors of visible light? Animation Animation Animation Animation

25. Types of light spectra Continuous Spectra All lines of color are continuously emitted (Also known as white light) Line Spectra Only certain lines of color are seen

26. Excited Electrons and Spectra • Line spectra - when light emitted by atoms of an element is passed through a prism, only very specific colors come out, and not a rainbow • Elements can be identified by their unique line spectra • Many elements were discovered this way! • Janseen discovered He, by light from sun, in 1868. • Information known about extraterrestrial objects comes from emitted light. Carbon Helium Neon

27. Line Spectra Diagram for Hydrogen • The lines of light we see correspond to electrons moving from one energy level to another! • The greater the fall, the more the energy they release!

29. Electrons in Energy Levels • The maximum number of electrons in any energy level is = 2n2 • Level 2n2 maximum number of electrons • 1 2(1)2 2 • 2 2(2)2 8 • 3 2(3)2 18 • 4 2(4)2 32

30. Now we are done redesigning the atom, right….? • Wrong! • 1924 Louis DeBroglie proposed that because light waves act somewhat like matter, then matter must act like light waves! • That means that all matter - ducks, bowling balls, planes, electrons, even you and me - all travel in waves! • This didn’t make sense, since most people could see that most objects traveled in straight lines! ?

31. Hydrogen Atom But all matter does travel in waves! • In 1927, 2 scientists at Bell Laboratories proved that DeBroglie was right! • They took X-Ray Crystallography pictures of atoms, and saw that electrons actually traveled in waves! • This caused the model of the atom to be redesigned even again!

32. If all matter travels in waves, then why can we not see the wave motion of normal objects? • If you were to measure the wavelength of a duck, or plane, or bee, you would see relative to the size of the object, and its wavelength would be incredibly tiny! • Electrons are so incredibly small already! • This means that the wavelength of an electron is relatively large compared to its size! • Its wavelike motion is going to affect the atom and its structure…

33. Animation

34. Another problem with the puzzle…. • Werner Heisenberg, a famous German scientist, suggested that it was impossible to know exactly where an electron was at all times! • To watch an electron orbit the nucleus would require light! • Shining light on an electron might do what….? • Move it! • And electrons are so small, and move so fast, that we would lose where it would go! • The Heisenberg Uncertainty Principle: It is impossible to simultaneously know an electron’s location and speed around the nucleus of an atom. Photon of light Unknown new location

35. So what does THAT mean??? • Electrons travel in waves around the nucleus, and we can’t be sure where they are some of the time! • Erwin Schrodinger used complicated mathematics and probability to calculate where electrons were most likely to be located. • This new model, called the Quantum Mechanical Model predicts the probability of where the electron is going to be 90% of the time! • It is also called the electron cloud model or the 90% probability model! • It means that we THINK that the electron is located in some region or “cloud” of space, 90% of the time! But if we went looking for it by shining light on it, it might move to some unpredictable location!

36. Sounds really vague and inaccurate, huh? • A model where we don’t know where the electron is??? • But Schrodinger did calculations to figure out exactly where in the energy levels we could probably find the electron…. • These locations were called sublevels…. • Even within these sublevels, Schrodinger figured out what shape an electron would be located in when it moved……called an orbital! • So remember, electrons don’t travel in nice circular orbits…they travel in unpredictable, wavelike patterns in a 3-dimensional area….These areas are called sublevels…..the electron could be there at any time! It would be like taking a snapshot picture….The orbital is a collection of all of the potential snapshots…

37. Why do we care about where the electrons are so much??? • The electrons are the outside part of the atom! • They are the only part of the atom that can be added or removed! • They are what make an atom “react”! Where they are has everything to do with how an atom will “react”! • There isn’t much room in the 1st energy level, so it only has one sublevel, or area that the electron can exist in - • It is called the “s” sublevel. • It has one orbital, shaped like a sphere • Every energy level, in fact, has an “s” sublevel, because it simply means that the electron is moving in a sphere!

38. Each energy level has an “s” sublevel • Each “s” sublevel has only one orbital, shaped as a sphere • Notice that it looks as if there are hundreds of electrons in each “s” sublevel; this is actually only one electron. We are looking at the electron in all of its possible locations at once! • Each “s” sublevel, being a small sphere, can only hold 2 electrons, no matter what energy level it is in! • That means the 1st energy level can only hold 2 electrons total! e- e- e- e- e- e-

39. The second energy level is larger, and has more room for electrons! • The 2nd level has 2 types of sublevels - an “s” and a “p” sublevel • p sublevels are shaped like dumbbells • Where the “s” sublevel only had one orbital, the p sublevel has 3 “orbitals” or shapes! • Each orbital is identical in shape, except for its orientation in space! • Each orbital in the “p” sublevel can hold a maximum of 2 electrons, so any “p” sublevel can hold a maximum of 6 electrons total! • Remember - when talking about a “p” sublevel, you aren’t referring to a particular energy level - you are saying something about how an electron moves! • You are saying it exists in a dumbbell-like space!

40. Shapes of “p” Orbitals e- e- e- e- e- e- e- e- e- e- e- e-

41. So how many electrons can the 2nd energy level TOTAL? • The 2nd energy level has a “s” sublevel, with 1 orbital, and a “p” sublevel, with 3 orbitals • Each orbital can hold 2 e- maximum! • Total of 8 e-!

42. e- e- e- e- e- e- e- e- e- e- • The 3rd energy level has 3 sublevels - an “s”, a “p”, and a “d” sublevel • The “d” sublevel has 5 “orbitals” or shapes • With each holding 2 e-, the “d” sublevel can hold a maximum of 10 e- • This allows the 3rd energy level total to hold….. • 18 e-!

43. An atom with 3 energy levels can hold a maximum of how many electrons, then? • 28 e-! • 2 in the first energy level - 2 in the “s” sublevel • 8 in the second energy level - 2 in the “s” sublevel, and 6 in the “p” sublevel • 18 in the third energy level - 2 in the “s” sublevel, and 6 in the “p” sublevel, and 10 in the “d” sublevel

44. Some hints…. Any energy level “n” has exactly n sublevels in it Each sublevel has a specific number of orbitals, as seen on the chart below Since electrons don’t like each other, having the same charge and repelling each other, an orbital can hold a maximum of only 2 e-. This is known as the Pauli Exclusion Principle. Remember - a sublevel simply tells us where an electron is located, and an orbital tells us something about the shape that it moves within as it travels in a wave! level sublevel No. of orbital Max no. of e- 1 s 1 2 sublevel No. of orbital Max no. of e- 2 s p 1 3 2 6 s 1 2 p 3 6 3 s p d 1 3 5 2 6 10 d 5 10 f 7 14 8 18 n # sublevels “names” 1 1 s 2 2 s, p 3 3 s, p, d 4 4 s, p, d, f 5 4 s, p, d, f

45. s, p, d, and f Orbitals Insert figure 5.31

46. Who wants to draw complicated atoms with these sublevels and orbitals included in the picture…? • Instead, we can use shorthand for where the electrons are located! • There are two shorthand ways of indicating where electrons are located: • Electron Configurations • Orbital Diagrams • Let’s look at each and discuss why we use them!

47. Electron Configurations • We use this shorthand to indicate where electrons live… • We use numbers to indicate the energy level, letters to indicate the shape or sublevel, and superscripts (exponents) to indicate how many electrons there are in a particular sublevel! • For example, Lithium would be written as: • Li = 1s22s1 • Notice there are 3 electrons total - 2 electrons in the s sublevel of the 1st energy level, and 1 electron in the s sublevel of the 2nd energy level! # of electrons Li = 1s22s1 sublevel energy level

48. What energy level would an electron fill first…? • The lowest possible energy level, of course! • Electrons are negative! • They want to be as close to the nucleus as possible! • This is the lowest energy, most stable location.. • This is known as the Aufbau Principle… • Electrons fill lowest energy levels first! • Can we write the electron configuration for sodium, then? • Sodium has…. • 11 electrons! • We know that electrons would first occupy the first energy level! • Once that is filled, they would then fill the second, and then the third, etc. Na = 1s22s22p63s1

49. Inverted Triangle Apartment Building Floor = n Apt = orbital (s, p, d, f) s = 1 bedroom = 2 e- p = 3 bedroom = 6 e- d = 5 bedroom = 10 e- f = 7 bedroom = 14 e- (2 e- per room)

50. Electron Configurations Notice the violation of the Aufbau Principle….