Chapter 11a Modern Atomic Theory

11.1 Rutherford’s Atom 11.2 Electromagnetic Radiation 11.3 Emission of Energy by Atoms 11.4 The Energy Levels of Hydrogen 11.5 The Bohr Model of the Atom

Nuclear Model of the Atom The atom has a small dense nucleus which is positively charged. contains protons (+1 charge). contains neutrons (no charge). The remainder of the atom is mostly empty space. contains electrons (–1 charge). 

What are the electrons doing? The nuclear charge (n+) is balanced by the presence of n electrons moving in some way around the nucleus. What are the electrons doing? How are the electrons arranged and how do they move? Copyright © Cengage Learning. All rights reserved

Wavelength ( ) – distance between two peaks or troughs in a wave. Characteristics Wavelength ( ) – distance between two peaks or troughs in a wave. 

Different Wavelengths Carry Different Amounts of Energy

One of the ways that energy travels through space.

Speed (c) – speed of light (2.9979×108 m/s) Characteristics Frequency ( ) – number of waves (cycles) per second that pass a given point in space Speed (c) – speed of light (2.9979×108 m/s) 186,000 miles/s

Photon – packet of energy Dual Nature of Light Wave Photon – packet of energy

Characteristics Energy of a photon of light = Planck’s constant (h) (6.626 x 10-34Js) times the speed of light (c) (2.9979×108 m/s) divided by the wavelength in meters (λ) or the wavelength in nanometers (nm) times ten to the -9 power (550nm = 550 x 10-9m). OR: Ephoton = (hc) / λ

Let’s Practice! E=hc/λ =6.626 x 10-34Js(3.00 x 108m/s)/(535 x 10-9m) What is the energy of light with a wavelength of 535 nm? E=hc/λ =6.626 x 10-34Js(3.00 x 108m/s)/(535 x 10-9m) =3.70 x 10-19 J

Seeing the Light-A New Model of the Atom Maxwell Planck-Black Body Radiation 1900—Nobel Prize in 1918 Found that blackbody radiation was quantized.

Quantized Energy Levels The energy levels of all atoms are quantized.

Einstein’s Photoelectric Effect (1905--Nobel Prize in 1921) Only light from a certain color (energy) could eject electrons. Intensity of the light had no effect. Energy is absorbed only at quantized energies!

Atoms can give off light. They first must receive energy and become excited. The energy is released in the form of a photon. The energy of the photon corresponds exactly to the energy change experienced by the emitting atom. Copyright © Cengage Learning. All rights reserved

Excited state – atom with excess energy Atomic states Excited state – atom with excess energy Ground state – atom in the lowest possible state When an H atom absorbs energy from an outside source it enters an excited state. Copyright © Cengage Learning. All rights reserved

Energy Level Diagram Energy in the photon corresponds to the energy used by the atom to get to the excited state. Copyright © Cengage Learning. All rights reserved

Stokes Shift-Absorb high energy (UV) and emit low energy (visible).

Only certain types of photons are produced when H atoms release energy Only certain types of photons are produced when H atoms release energy. Why?

Line Spectra http://jersey.uoregon.edu/vlab/elements/Elements.html

The word laser comes from light amplification by stimulated emission of radiation.

Lasers Lasers used to remove blood clots. Laser light transmitted in fiber optics. Cataract Removal Light Shows

Holograms 3D pictures made by Lasers using the interference pattern between reflected laser light from the surface of an object and the undisturbed laser light reflected from a mirror. The Interference pattern is recorded on film. The developed film can then be used by a laser to recreate the image in 3D. http://www.youtube.com/watch?v=wrxUYzWASvE http://www.youtube.com/watch?v=E4A_u67EKnU&feature=fvw https://www.youtube.com/watch?v=AXhGfkGh4vM http://www.youtube.com/watch?v=cAX8uSc8Fnk&NR=1

Holograms Holograms are made from laser light without using an image forming device. Tupac holographic concert and a holographic fashion display. http://www.youtube.com/watch?v=mcSYpZchFpI http://www.youtube.com/watch?v=Zf_eXDPElh0 https://www.youtube.com/watch?v=89KxxpmMhi4

The Doppler Effect The doppler effect is the apparent change in frequency of a wave due to the relative motion of the listener and the source of the sound. The doppler effect also occurs in light waves and is used by astronomers to calculate the speed at which stars are approaching or receding.

Bohr Model Line Spectra in Stars and the red shift indicating movement away or towards us. 7 -

Quantized Energy Levels Since only certain energy changes occur the H atom must contain discrete energy levels. Copyright © Cengage Learning. All rights reserved

Concept Check Why is it significant that the color emitted from the hydrogen emission spectrum is not white? How does the emission spectrum support the idea of quantized energy levels? If the levels were not quantized, we’d probably see white light. This is because all possible value of energy could be released, meaning all possible colors would be emitted. All the colors combined make white light. Since only certain colors are observed, this means that only certain energy levels are allowed. An electron can exist at one level or another, and there are regions of zero probability in between.

When an electron is excited in an atom or ion Concept Check When an electron is excited in an atom or ion a) only specific quantities of energy are released in order for the electron to return to its ground state. b) white light is never observed when the electron returns to its ground state. c) the electron is only excited to certain energy levels. d) All of the above statements are true when an electron is excited. The correct answer is d. Copyright © Cengage Learning. All rights reserved

Niels Bohr 1913—Nobel Prize in 1922 Niels Bohr hypothesized that electrons orbit the nucleus just as the planets orbit the sun (planetary model). Niels Bohr 1913—Nobel Prize in 1922 Quantized energy levels Electron moves in a circular orbit. Electron jumps between levels by absorbing or emitting a photon of a particular wavelength. Actually electrons do not move in a circular orbit.

D Chapter 11b Modern Atomic Theory

Modern Model of the Atom Chapter 11 Modern Model of the Atom 11.6 The Wave Mechanical Model of the Atom 11.7 The Hydrogen Orbitals 11.8 The Wave Mechanical Model: Further Development 11.9 Electron Arrangements in the First Eighteen Atoms on the Periodic Table 11.10 Electron Configurations and the Periodic Table 11.11 Atomic Properties and the Periodic Table

Orbitals Nothing like orbits Probability of finding the electron within a certain space This model gives no information about when the electron occupies a certain point in space or how it moves.

Orbitals Orbitals do not have sharp boundaries and are represented by probability distributions or where the electron is likely to be found without regards to movement of the electrons. Chemists arbitrarily define an orbital’s size as the sphere that contains 90% of the total electron probability. Copyright © Cengage Learning. All rights reserved

Scanning Tunneling Microscope

Louis DeBroglie 1924 – Nobel Prize in 1929 He found that matter (electrons) moved in waves. Just as light behaved like particles and waves, so did matter. An 18-wheeler moving down Hwy 99 at 60mph has a wavelength smaller than an atom. However, an electron (very light) moves much faster and its wavelength is much larger than its size.

Erwin Schrödinger 1926 -Nobel Prize in 1933 Found the probability of finding an electron in an atom.

Erwin Schrödinger 1926 -Nobel Prize in 1933 Found the probability of finding an electron in an atom.

Hydrogen Energy Levels Hydrogen has discrete energy levels. Called principal energy levels Labeled with whole numbers

Hydrogen Energy Levels Each principal energy level is divided into sublevels. Labeled with numbers and letters Indicate the shape of the orbital Copyright © Cengage Learning. All rights reserved

Hydrogen Energy Levels The s and p types of sublevel Copyright © Cengage Learning. All rights reserved

d Orbitals 7 -

f-orbtals http://www.d.umn.edu/~pkiprof/ChemWebV2/AOs/ao4.html

Why the different shapes? 3py 3d 2py 1s 2s 3s 2px 3px 2pz 3pz

The number tells the principal energy level. Orbital Labels The number tells the principal energy level. The letter tells the shape. The letter s means a spherical orbital or shape of the probability distribution of the electron. The letter p means the orientation. The x, y, or z subscript on a p orbital label tells along which of the coordinate axes the two lobes lie.

Why does an H atom have so many orbitals and only 1 electron? Hydrogen Orbitals Why does an H atom have so many orbitals and only 1 electron? An orbital is a potential space for an electron. Atoms can have many potential orbitals.

Atoms Beyond Hydrogen The Bohr model was discarded because it does not apply to all atoms. It did not consider the different energy sublevels or suborbitals within each orbital. Atoms beyond hydrogen have multiple electrons that distorts the energy levels due to electron-electron interactions. Need one more property to determine how the electrons are arranged: Spin – electrons spin like a top causing a magnetic field. Opposite magnetic fields can attract allowing electrons to occur in pairs if their spin or magnetic field is opposite.

Atoms Beyond Hydrogen Pauli Exclusion Principle – an atomic orbital can hold a maximum of 2 electrons and those 2 electrons must have opposite spins.

Principal Components of the Wave Mechanical Model of the Atom Atoms have a series of energy levels called principal energy levels (n = 1, 2, 3, etc.). The energy of the level increases as the value of n increases. Each principal energy level contains one or more types of orbitals, called sublevels. The number of sublevels present in a given principal energy level equals n. Copyright © Cengage Learning. All rights reserved

Principal Components of the Wave Mechanical Model of the Atom 5. The n value is always used to label the orbitals of a given principal level and is followed by a letter that indicates the type (shape) of the orbital (1s, 3p, etc.). 6. An orbital can be empty or it can contain one or two electrons, but never more than two. If two electrons occupy the same orbital, they must have opposite spins. Copyright © Cengage Learning. All rights reserved

Principal Components of the Wave Mechanical Model of the Atom 7. The shape of an orbital does not indicate the details of electron movement. It indicates the probability distribution for an electron residing in that orbital.

Concept Check Which of the following statements best describes the movement of electrons in a p orbital? a) The electron movement cannot be exactly determined. b) The electrons move within the two lobes of the p orbital, but never beyond the outside surface of the orbital. c) The electrons are concentrated at the center (node) of the two lobes. d) The electrons move along the outer surface of the p orbital, similar to a “figure 8” type of movement. The correct answer is a. Copyright © Cengage Learning. All rights reserved

Energy Level Diagram for Carbon

Electron configuration – electron arrangement 1s1 H Atom Electron configuration – electron arrangement 1s1 Orbital diagram – orbital is a box grouped by sublevel containing arrow(s) to represent electrons Copyright © Cengage Learning. All rights reserved

Electron configuration 1s2 2s1 Orbital diagram Li Atom Electron configuration 1s2 2s1 Orbital diagram Copyright © Cengage Learning. All rights reserved

O Atom The lowest energy configuration for an atom is the one having the maximum number of unpaired electrons in a particular set of degenerate (same energy) orbitals. Oxygen: 1s 2s 2p Copyright © Cengage Learning. All rights reserved

The electron configurations in the sublevel last occupied for the first eighteen elements. Copyright © Cengage Learning. All rights reserved

Classifying Electrons Core electrons – inner electrons Valence electrons – electrons in the outermost (highest) principal energy level of an atom 1s22s22p6 (valence electrons = 8) The elements in the same group on the periodic table have the same valence electron configuration. Elements with the same valence electron arrangement show very similar chemical behavior.

3d suborbitals Concept Check How many unpaired electrons does the element cobalt (Co) have in its lowest energy state? a) 0 b) 2 c) 3 d) 7 3d suborbitals The correct answer is c. There are 7 electrons in the d orbitals, with two of the d orbitals containing paired electrons and three of the d orbitals containing unpaired electrons. Copyright © Cengage Learning. All rights reserved

a) Yes. An electron can be excited into a 3d orbital. Concept Check Can an electron in a phosphorus atom ever be in a 3d orbital? Choose the best answer. a) Yes. An electron can be excited into a 3d orbital. b) Yes. A ground-state electron in phosphorus is located in a 3d orbital. c) No. Only transition metal atoms can have electrons located in the d orbitals. d) No. This would not correspond to phosphorus’ electron arrangement in its ground state. The correct answer is a. Copyright © Cengage Learning. All rights reserved

Quantum #’s are like an Address. What do you need to know to find out where you live? State City Street House Magnetic Quantum # (ml) Spin Quantum # (ms) Principle Quantum # (n) Angular Quantum # (l)

Look at electron configurations for K through Kr. Copyright © Cengage Learning. All rights reserved

Orbital Filling and the Periodic Table Copyright © Cengage Learning. All rights reserved

Orbital Filling In a principal energy level that has d orbitals, the s orbital from the next level fills before the d orbitals in the current level. After lanthanum, which has the electron configuration [Xe]6s25d1, a group of fourteen elements called the lanthanide series, or the lanthanides, occurs. This series of elements corresponds to the filling of the seven 4f orbitals. Copyright © Cengage Learning. All rights reserved

Orbital Filling 3. After actinum, which has the configuration [Rn]7s26d1,a group of fourteen elements called the actinide series, or actinides, occurs. This series corresponds to the filling of the seven 5f orbitals.

Orbital Filling 4. Except for helium, the group numbers indicate the sum of electrons in the ns and np orbitals in the highest principal energy level that contains electrons (where n is the number that indicates a particular principal energy level). These electrons are the valence electrons.

Exercise Determine the expected electron configurations for each of the following. a) S 1s22s22p63s23p4 or [Ne]3s23p4 b) Ba [Xe]6s2 c) Eu [Xe]6s24f7 a) 16 electrons total; 1s22s22p63s23p4 or [Ne]3s23p4 b) 56 electrons total; [Xe]6s2 c) 63 electrons total; [Xe]6s24f7 Copyright © Cengage Learning. All rights reserved

Write electron configurations for the following: Al Sc K Br Zn Hg 1s22s22p63s23p1 1s22s22p63s23p64s23d1 1s22s22p63s23p64s1 1s22s22p63s23p64s23d104p5 1s22s22p63s23p64s23d10 1s22s22p63s23p64s23d104p65s24d105p66s2 4f145d10 7 - Copyright © Cengage Learning. All rights reserved

Write the abbreviated electron configuration for the following: Magnesium Carbon Boron Chlorine Selenium – [Ne] 3s2 – [He] 2s22p2 – [He] 2s22p1 – [Ne] 3s23p5 – [Ar] 4s23d104p4 7 - Copyright © Cengage Learning. All rights reserved

[Kr] isoelectronic with Kr [Ne] isoelectronic with Ne Write the electron configuration in long and abbreviated notation for the following ions. Br- N3- K+ Sr2+ S2- Ni2+ [Kr] isoelectronic with Kr [Ne] isoelectronic with Ne [Ar] isoelectronic with Ar [Kr] isoelectronic with Kr [Ar] isoelectronic with Ar [Ar]4s23d6 isoelectronic with Fe 7 - Copyright © Cengage Learning. All rights reserved

Metals tend to lose electrons to form positive ions. Metals and Nonmetals Metals tend to lose electrons to form positive ions. Nonmetals tend to gain electrons to form negative ions. Copyright © Cengage Learning. All rights reserved

Energy required to remove an electron from a gaseous atom or ion. Ionization Energy Energy required to remove an electron from a gaseous atom or ion. X(g) → X+(g) + e– Mg → Mg+ + e– I1 = 735 kJ/mol (1st IE) Mg+ → Mg2+ + e– I2 = 1445 kJ/mol (2nd IE) Mg2+ → Mg3+ + e– I3 = 7730 kJ/mol *(3rd IE) *Core electrons are bound much more tightly than valence electrons. Copyright © Cengage Learning. All rights reserved

Ionization Energy In general, as we go across a period from left to right, the first ionization energy increases. Why? Electrons added in the same principal quantum level do not completely shield the increasing nuclear charge caused by the added protons. Electrons in the same principal quantum level are generally more strongly bound from left to right on the periodic table. Copyright © Cengage Learning. All rights reserved

In general, as we go across a period the ionization energy increases. As we go up a group from top to bottom, the first ionization energy increases.

Which atom would require more energy to remove an electron? Why? Na Cl Concept Check Which atom would require more energy to remove an electron? Why? Na Cl Cl would require more energy to remove an electron because the electron is more tightly bound due to the increase in effective nuclear charge. Copyright © Cengage Learning. All rights reserved

Which atom would require more energy to remove an electron? Why? Li Cs Concept Check Which atom would require more energy to remove an electron? Why? Li Cs Li would require more energy to remove an electron because the outer electron is on average closer to the nucleus (so more tightly bound). Copyright © Cengage Learning. All rights reserved

In general atomic radius increases in going down a group. Atomic Size In general as we go across a period from left to right, the atomic radius decreases. Effective nuclear charge increases, therefore the valence electrons are drawn closer to the nucleus, decreasing the size of the atom. In general atomic radius increases in going down a group. Orbital sizes increase in successive principal quantum levels. Copyright © Cengage Learning. All rights reserved

Relative Atomic Sizes for Selected Atoms (Fig. 11-36) Copyright © Cengage Learning. All rights reserved

Which should be the larger atom? Why? Na Cl Concept Check Which should be the larger atom? Why? Na Cl Na should be the larger atom because the electrons are not bound as tightly due to a smaller effective nuclear charge.

Which should be the larger atom? Why? Li Cs Concept Check Which should be the larger atom? Why? Li Cs Cs should be the larger atom because of the increase in orbital sizes in successive principal quantum levels (to accommodate more electrons). Copyright © Cengage Learning. All rights reserved

Which is lower in energy? Concept Check Which is larger? The hydrogen 1s orbital The lithium 1s orbital Which is lower in energy? The hydrogen 1s orbital is larger because the electrons are not as tightly bound as the lithium 1s orbital (lithium has a higher effective nuclear charge and will thus draw in the inner electrons more closely). The lithium 1s orbital is lower in energy because the electrons are closer to the nucleus. Copyright © Cengage Learning. All rights reserved

Exercise Arrange the elements oxygen, fluorine, and sulfur according to increasing: Ionization energy S, O, F Atomic size F, O, S Ionization Energy: S, O, F (IE increases as you move up a column and to the right across a period.) Atomic Size: F, O, S (Atomic radius increases as you move to the left across a period and down a column.) Copyright © Cengage Learning. All rights reserved