Chapter 7 Problems: 16, 17, 19 23, 26, 27, 30, 31, 34, 38 41, 45, 49, 53, 60, 61, 65, 67, 75, 79, 80, 83, 87, 90, 91, 94, 95, 97, 101, 111, 113, 115

Transcription

1 Chapter 7 Problems: 16, 17, 19 23, 26, 27, 30, 31, 34, 38 41, 45, 49, 53, 60, 61, 65, 67, 75, 79, 80, 83, 87, 90, 91, 94, 95, 97, 101, 111, 113, , 121, 122, 125a

2 Chapter 7 Atomic Structure and Periodicity 4 primary characteristics of waves: 1) Wavelength (λ) the distance between successive peaks in a wave. 2) Frequency (υ) The number of waves passing a point per unit of time. 1 Hertz (Hz) = 1 wave per second. 3) Amplitude height of wave. 4) Speed sound travels around 1000 feet/ second light travels 186,000 miles/ second (3 x 10 8 m/sec)

3 Light Electromagnetic Radiation Energy that travels through space in the form of waves, and having fluctuating electrical and magnetic fields.

4 High energy Low Energy

5 All forms of light travel the same speed. What is the relationship between wavelength and frequency? C = λ υ where c = speed of light (meters/second) (λ) = wavelength (meters) (υ) = frequency ( 1 ) second

6 C = λ υ where c = speed of light (meters/second) (λ) = wavelength (meters) (υ) = frequency ( 1 ) second Problem: Calculate the wavelength of Alice, MHz radio waves. Problem: Calculate the wavelength of KOA, 850 KHz radio waves, and compare to Alice.

7 Max Planck (1900) found that heated objects didn t emit energy of any quantity, but rather, gave off whole number amounts of energy. Planck coined the term quantum the smallest, whole number amount of light energy that can be emitted or absorbed. Examples of a quantum of: pop in a pop machine? Tires at the tire store? Babies at the hospital? Gasoline at the gas pump? Light?

8 The energy of multiple waves of light can be calculated: E = n h υ where E = energy (Joules) n = number of waves (whole number) h = Plancks constant = 6.63 x J. sec υ = frequency (sec -1 ) And the energy of a single wave: E = h υ Light is quantized it comes in whole number multiples of the basic unit.

9 Problem: Determine the energy of a photon (1 wave) of x-ray (5.00 x 10-2 nm) light. Compare to a photon of Infrared radiation (5.00 x 10 4 nm)

10 Problem: H 2 O (l) + light H 2(g) + ½ O 2(g) H = kj Determine the minimum wavelength of light to photo-dissociate a molecule of water. Assume that 1 photon will dissociate 1 molecule of water, if it has enough energy.

11 The Photoelectric Effect: (Einstein won a Nobel Prize in 1921 for this discovery) Determined that light acts like a particle. When light of short enough wavelength is shone in alkali metals, electrons are ejected from the metal surface. The number of electrons ejected are proportional to the light intensity, or volume of light. The energy of the electrons ejected is proportional to the wavelength of light, where the shorter the wavelength, the higher the energy of the ejected electrons. Einstein reasoned that light was acting like a particle, which he called a photon. If the photon had sufficient energy in a collision with an electron, the photon would knock the electron out of its orbital.

12 Wave/Particle Duality of Light Einstein suggested particle-like properties of light could explain the photoelectric effect. But diffraction patterns suggest photons are wave-like.

13 Einstein also determined that mass and energy were related, through his famous equation, E = mc 2 where E = energy (Joules) m = mass (kg) c = speed of light (m/sec) This re-arranges to m = E c 2 And E = hc λ We can calculate the apparent mass of a photon of light.. m = h/λ c

14 The dual nature of light light has both wave and particle like properties. As a wave: Louis DeBroglie (1923) reasoned that if light could behave like a particle, then electrons, which until now were considered to be a particle, could have wavelike properties. As a stream of particles: By re-arranging Einstein and Plancks Equations: λ = h mc where c is the speed of light for a photon, or the velocity of an object. This equation is used to calculate the wavelength of any moving particle!

15 Problem: Compare the wavelength of: a) electron (9.11 x kg) traveling 1.0 x 10 7 m/sec. b) ball (.10 kg) traveling 35 m/sec. Note the relationship: The smaller the object, the larger the wavelength The larger the object, the smaller the wavelength. Very Cool Stuff! Energy is a form of matter large objects have un-measurable wavelengths, and display predominantly particle like behavior. Small objects, like photons of light, exhibit predominantly wavelike behavior, and barely perceptible particle like behavior. Medium size objects (electrons) display both wave and particle like behavior.

16 Continuous spectrum all colors of light are present Bright Line spectrum only certain colors of light are present Absorption Spectrum opposite of a bright line spectrum These 2 types of spectra are used to identify one element or compound from another. These bands of light are caused when electrons absorb external energy and jump to a higher energy level. This is unstable, so they fall back to their lower energy level, emitting a photon of light.

17 Neils Bohr noticed that Hydrogen gas emitted only 4 bands of light in its bright line spectra, and these lines were always absent in the absorption spectra. Since the type of light emitted didn t shift, the energy levels that the electrons exist in must be quantized the electrons only exist in certain energy levels, and can only be excited to other given energy levels. Decided that the Hydrogen atom looked like this:

18 Ground State the lowest energy level an electron can exist in. Excited State an electron that has absorbed external energy, and exists in a higher energy state. To calculate the energy of an electron in Hydrogen at different energy levels: E n = -R H ( 1 ) where R H = Rydberg Constant n 2 = x J Problem: Calculate the energy of an electron in the third energy level. Calculate the energy of an electron in the second energy level. Calculate the energy released when an electron falls from the third to second energy level. Determine the color of light.

19 An easier formula for the previous problem: (this solves energy per photon!) E photon = -R H ( 1-1 ) n 2 f n 2 i Problem: How much energy is required to remove an electron in the first energy level? Unfortunately, the only element that Bohr s model successfully predicts is Hydrogen.

20 Erwin Schrodinger (mid 1920 s) determined formulas to describe electrons as waves rather than particles.

21 Schrodingers formulas calculated regions in space around a nucleus where an electron is likely to be found, and diagramed as an electron density map. An orbital is constructed by enclosing the region where the electron is found 90% of the time. This is an s orbital. 3 orientations of p orbitals

22 7 orientations of f orbitals 5 orientations of d orbitals

23 It is very difficult to determine the path of an electron. The smaller an object, the more influenced the particle is by the device you use to measure it. This is called The Uncertainty Principle, developed by Werner Heisenberg It is impossible to know, simultaneously, the position and momentum of a particle with certainty.

24 A set of 4 quantum numbers is used to describe each electron. 1) Principal Quantum number: n = 1,2,3,.. describes the energy level, or the shell of an electron, and the size of the orbital. 2) Angular Momentum Quantum Number: l = 0 (n 1) (whole numbers) Describes the type of the sublevel. l = 0 s sublevel l = 1 p sublevel l = 2 d sublevel l = 3 f sublevel 3) Magnetic Quantum Number: m l = -l to +l (whole numbers) Relates the position of the orbital to an x, y, z axis, and determines the # of orbitals in a sublevel. where l = 0 m l = 0 indicates 1 orientation l = 1 m l = -1, 0, 1 indicates 3 orientations. 4) Spin Quantum Number: m s = +1/2 or -1/2 Describes the spin of an electron. Scientists noticed that an electron has a magnetic moment with two possible orientations when place in a magnetic field. Since magnetic moments are caused by spinning objects, there are 2 spin states.

25 More detailed look at orbitals: How many orientations are available for a 1s sublevel? 2s? 2p?

26 Radial Probability Density Graph: plots radius (x) vs. rpd (y)

27 p orbital l = 1 Radial probability vs. radius for a 2p sublevel. What would a 3p orbital look like? How many orientations are available for a 2p sublevel? 3p?

28 d orbital l = 2 How many orientations? f orbital l = 3 How many orientations?

29 Problem: How many sublevels can the 5 th energy level have? Problem: What is the total number of orbitals in the third energy level? For H, the energy of an electron is determined by n 1s < 2s = 2p < 3s = 3p = 3d.. (called degenerate orbitals same energy orbitals) For all other atoms, the energy of an electron is determined by n + l 1s < 2s < 2p < 3s < 3p < 3d

30 Pauli Exclusion Principle No 2 electrons in an atom can have identical quantum numbers. Hunds Rule The most stable arrangement of electrons in a subshell is with the greatest number of parallel spins. Aufbau Principle as protons are added to an atom, so are electrons, 1 for 1 Problem: Write the 4 quantum numbers for all electrons in an atom of calcium. Recall, electrons will fall to the lowest available energy level possible.

31 Why is 2s preferable (lower in energy) than 2p in a multiple electron atom? Shielding: inner electrons shield outer electrons from protons, 1 for 1 outer electrons shield outer electrons from protons ineffectively.

32 Penetration Effect While the 2p has its maximum probability closer to the nucleus, the small hump of the 2s orbital makes this 2s orbital more penetrating toward the nucleus than the 2p orbital. As distance increases between 2 charged particles, attraction dramatically decreases.

33 Restated: The more effectively an orbital allows its electrons to penetrate the shielding electrons, the lower the energy of that electron orbital.

34 Link to laser

35 The Periodic Table Dmitri Mendeleev ( ) * Youngest of 17 children * Cut hair once per year * Founder of the modern periodic table * Organized elements according to their chemical and physical properties. * Left spaces for elements that were unknown at the time, and accurately predicted properties of those soon to be discovered elements.

36 Henry Mosley (1913) arranged atoms by atomic number. (the ability to determine the number of protons was now available) Tweaked Mendeleev s table to what we have now.

37 Problem: Write electron configurations for: F As Problem: Write electron configurations for ions of: N Ca Problem: Write a noble gas shorthand configuration for: Mo

38 Problem: Write an orbital diagram for S (hint..write the electron configuration first.) Some irregularities: Sc: [Ar]4s 2 3d 1 Ti: [Ar]4s 2 3d 2 V: [Ar]4s 2 3d 3 Cr: [Ar]4s 1 3d 5.. Cu: [Ar]4s 1 3d 10 ½ and completely filled d orbitals are stable Which other elements in the periodic table will be similar to Cr and Cu? 4s is filled before 3d because 4s is more penetrating, and therefore, less shielded.

39 After La (Lanthanum) [Xe]6s 2 5d 1, the lanthanides are filled with 4f electrons. The energy of 5d and 4f are very similar (5 + 2 = 7, = 7). The same is true for Ac.

40 Trends in the Periodic Table 1) Ionization energy energy required to remove an electron from a gaseous atom or ion. X (g) + energy X + (g) + e - Al (g) Al + (g) + e - I.E. 1 = 580 kj/mole Al + (g) Al +2 (g) + e - I.E. 2 = 1815 kj/mole Al +2 (g) Al +3 (g) + e - I.E. 3 = 2740 kj/mole Al +3 (g) Al +4 (g) + e - I.E. 4 = 11,600 kj/mole

41 Ionization energy trends in the Periodic Table: 1) Going Left to Right, first ionization energy generally increases. a) inner electrons completely shield outer electrons from the nucleus b) outer electrons incompletely shield other outer electrons from the nucleus. Exceptions: Be (1s 2 2s 2 ) B (1s 2 2s 2 2p 1 ) This electron is added to a well shielded 2p orbital. Note that this trend occurs 3 periods down group 13. Note that N (1s 2 2s 2 2p 3 ) O (1s 2 2s 2 2p 4 ) This electron is being added to a half filled 2p orbital, and must pair up with an electron already in the orbital. The repulsion causes the electron to be more easily removed. Occurs 3 periods down the group. Ionization energy decreases going down a group. As the distance between 2 oppositely charged particles increases, the force of attraction decreases.

42 Different view of the same thing.

43 2. Electron Affinity The energy change associated with adding an electron to an atom. X (g) + e - X - (g) Generally, EA increases going left to right through a period. EA decreases going down a group.

44 Electron Affinity exceptions: Period 2: Be 1s 2 2s 2 added electron goes into 2p, and completely shielded, therefore, has no attraction to the nucleus, and the electron will not stay. Period 15: N 1s 2 2s 2 2p 3 added electron goes into a half filled orbital, and the repulsion encountered causes excess shielding. Period 18: Ne 1s 2 2s 2 2p 6 added electron goes into 3s, where the electron is completely shielded, and will not stick. These trends continue down each group to some extent.

45 3) Atomic Radius (size of an atom) - defined by the size of the electron cloud. Trend: Size increases going down a group, because a new shell of electrons is added each time. Size decreases going Left to Right across a period, for the same reason that ionization energy increases less shielding. Also note that as electrons are added, size increases. As electrons are removed, size decreases. Remove electrons Add electrons

46 Problem: Arrange from largest to smallest: 1) Ca Mg Sr 2) Li O C 3) Cl - Ar K + 4) Fe Fe +2 Fe +3 5) S Se Cl

47 Group 1, 2, Representative Elements Each family has elements in it with similar chemical properties. Inner Transition Elements

48 Alkali Metal Family: All have ns 1 electron configuration, and therefore, have low first ionization, high second ionization energy. All are very reactive, and never found pure in nature. React with O 2 Li + O 2 Li 2 O lithium oxide (all alkali metals form oxides) Na + O 2 Na 2 O 2 sodium peroxide (sodium and below form peroxides) K + O 2 KO 2 potassium superoxide (potassium and below form superoxides. All alkali metals react with water: Na (s) + H 2 O (l) NaOH (aq) + H 2(g) Problem: Write an equation of Potassium + water