3/26/10. Light carries energy in waves. Units for wavelength, λ meter 1 nm = 10-9 m 1 Angstrom (1 Å) = m

Transcription

1 Chpt 6 lectronic Structure of Atoms lectromagnetic Radiation Light Light carries energy in 2 ways: 1st is the Wave Model Amplitude ν. λ = c time Wavelength (lambda, λ) Frequency (nu, ν) Speed (c = 3.00 x 10 8 m/s) Light carries energy in waves Units for wavelength, λ meter 1 nm = 10-9 m 1 Angstrom (1 Å) = m ν. λ = c Units for frequency, ν 1 cycle/sec = 1/s = 1 s -1 = 1 Hertz (Hz) 1

2 Figure 6.4: lectromagnetic Spectrum Light carries energy in two ways 1. As waves 2. As particles (photons) Photon Model: Planck s equation (q. 6.2 and 6.3 on pages 215 and 217 of text) really means = h ν photon = h ν Continuous Spectrum All colors of light present: Line Spectrum; Only some colors of light present: nergy of ON photon of frequency, ν 2

3 number, n. lectronic Structure of Atoms and Quantum Numbers Rule 1: n = 1, 2, 3, 4,. (n! 0) nucleus in one of several different shapes called orbitals: s orbital p orbital d orbital These differently shaped orbitals are identified by the quantum number l (think of l as the number of rubber bands needed to make the shape from a spherical balloon.) Rule 2: For a given value of n, l can have any value from 0 to n-1; l = 0,, n-1 The number of orbitals of each type (s, p, d, etc.) is given by the quantum number m l. For a Rule 3: Rule 4: m s can only be + 1/2 or 1/2 corresponds to an orbital with a unique orientation in space. + 3/26/10 ach element has its own line spectrum. Bohr Model of the H Atom (1913) Atom like a miniature solar system Only certain e - orbits allowed Introduced Quantum #, n Ground state ( orbit) + xcited states (all higher n orbits) lectrons gain or lose energy as they change orbits Why?? nergy gained comes from absorbed light nergy lost is lost as light, = hν Conclusion: In atoms, energy is quantized; lectrons are only in specific energy levels ach element has its own unique set of energy levels Bohr Model of the Atom: lectrons in an atom can only be in discrete energy levels labeled by the principal quantum In the Bohr Model, energy levels correspond to circular orbits of different sizes; electrons in orbits further from the nucleus are in higher energy levels. Quantum Mechanical Model: lectrons do NOT orbit nuclei like planets around the sun- they are found in a volume around the given value of l, each value of m l For a given value of l, m l can have the values from - l to + l, therefore m l = - l,, 0,, + l. The number of m l values is equal to the number of orbitals of that type. A maximum of 2 electrons can be in any orbital and each has its own spin quantum number, m s explains line spectra 0 3

4 Bohr Model of the Atom: lectrons in an atom can only be in discrete energy levels labeled by the principal quantum number, n. + Rule 1: n = 1, 2, 3, 4,. (n! 0) In the Bohr Model, energy levels correspond to circular orbits of different sizes; electrons in orbits further from the nucleus are in higher energy levels. Quantum Mechanical Model: lectrons do NOT orbit nuclei like planets around the sun- they are found in a volume around the nucleus in one of several different shapes called orbitals: s orbital p orbital d orbital These differently shaped orbitals are identified by the quantum number l (think of l as the number of rubber bands needed to make the shape from a spherical balloon.) Rule 2: For a given value of n, l can have any value from 0 to n-1; l = 0,, n-1 The number of orbitals of each type (s, p, d, etc.) is given by the quantum number m l. For a Rule 3: Rule 4: m s can only be + 1/2 or 1/2 corresponds to an orbital with a unique orientation in space. can have the values from - l to + l, therefore values is equal to the number of orbitals of that type. number, n. lectronic Structure of Atoms and Quantum Numbers Rule 1: n = 1, 2, 3, 4,. (n! 0) nucleus in one of several different shapes called orbitals: s orbital p orbital d orbital These differently shaped orbitals are identified by the quantum number l (think of l as the number of rubber bands needed to make the shape from a spherical balloon.) Rule 2: For a given value of n, l can have any value from 0 to n-1; l = 0,, n-1 The number of orbitals of each type (s, p, d, etc.) is given by the quantum number m l. For a Rule 3: Rule 4: m s can only be + 1/2 or 1/2 corresponds to an orbital with a unique orientation in space. + 3/26/10 Print this handout from course website for reference lectronic Structure of Atoms and Quantum Numbers DeBroglie: Dual Nature of lectron Like photons, electrons have both particle and wave properties: λ = h/mv given value of l, each value of m l For a given value of l, m l m l = - l,, 0,, + l. The number of m l A maximum of 2 electrons can be in any orbital and each has its own spin quantum number, m s Bohr Model: For a stable electron orbit nλ = 2πr n(h/mv) = 2πr Bohr Model of the Atom: lectrons in an atom can only be in discrete energy levels labeled by the principal quantum In the Bohr Model, energy levels correspond to circular orbits of different sizes; electrons in orbits further from the nucleus are in higher energy levels. Quantum Mechanical Model: lectrons do NOT orbit nuclei like planets around the sun- they are found in a volume around the given value of l, each value of m l For a given value of l, m l can have the values from - l to + l, therefore m l = - l,, 0,, + l. The number of m l values is equal to the number of orbitals of that type. A maximum of 2 electrons can be in any orbital and each has its own spin quantum number, m s For a stable electron orbit: n(h/mv) = 2πr Heisenberg s Uncertainty Principle Can t know exact location (r) and exact momentum (mv) of an electron at the same time Bohr s Model fails! Led to: Quantum Mechanical Model of the Atom (1926) nergy of an electron in an atom is quantized. lectrons have both wave and particle properties. Uses Uncertainty Principle. The nergy of each electron and its possible locations are calculated in terms of probability! ORBITALS 4

5 Orbital = where there is a high (90%) probability of finding an e - around the nucleus. ach e - in an atom has 4 Quantum Numbers: nergy level or shell, n (size of orbital) Shape (of orbitals in a given subshell) l m l : Number of orbitals in subshell l l = 0 l = 1 l = 2 Direction of e - spin, m s Print this handout from course website for reference Rules for assigning quantum numbers lectronic Structure of Atoms and Quantum Numbers Bohr Model of the Atom: lectrons in an atom can only be in discrete energy levels labeled by the principal quantum number, n. + Rule 1: n = 1, 2, 3, 4,. (n! 0) In the Bohr Model, energy levels correspond to circular orbits of different sizes; electrons in orbits further from the nucleus are in higher energy levels. Quantum Mechanical Model: lectrons do NOT orbit nuclei like planets around the sun- they are found in a volume around the nucleus in one of several different shapes called orbitals: s orbital p orbital d orbital These differently shaped orbitals are identified by the quantum number l (think of l as the number of rubber bands needed to make the shape from a spherical balloon.) Rule 2: For a given value of n, l can have any value from 0 to n-1; l = 0,, n-1 The number of orbitals of each type (s, p, d, etc.) is given by the quantum number m l. For a given value of l, each value of m l corresponds to an orbital with a unique orientation in space. Value of l Type of orbital s p d f Rule 3: For a given value of l, m l can have the values from - l to + l, therefore m l = - l,, 0,, + l. The number of m l values is equal to the number of orbitals of that type. A maximum of 2 electrons can be in any orbital and each has its own spin quantum number, m s Rule 4: m s can only be + 1/2 or 1/2 5

6 Meanings: n = nergy level (aka shell ). Subshells are found within shells. l = Subshell. Orbitals are found within subshells. m l = Orientation of a specific orbital in space. m s = direction of electron spin: up or down One s orbital Three p orbitals l Quantum # Type of Orbital m l values (# of Orbitals) Max # of e - s per subshell 0 s p -1, 0, d -2, -1, 0, +1, f -3, -2, -1, 0, +1, +2, Summary ach subshell (l) contains orbitals (m l ) ach shell (n) contains n subshells n = 1 shell has 1 subshell (1s) n = 2 shell has 2 subshells (2s & 2p) n = 3 shell has 3 subshells (3s & 3p & 3d) n = 4 shell has 4 subshells (4s & 4p & 4d & 4f) each s subshell has 1 orbital each p subshell has 3 orbitals each d subshell has 5 orbitals each f subshell has 7 orbitals lectron Configuration of Atoms lectrons fill the lowest energy orbitals first: Five d orbitals Where are different orbitals found? Subshells (and orbitals) of a given l value are located as shown: s p s l =0 p d d l =2 l =1 f f l =3 6

7 Orbital nergies for Hydrogen For a Hydrogen Atom, orbitals in the same energy level, n, have the same energy (they are degenerate ) Orbital nergies of Atoms w/ more than one electron are not degenerate Fig p 3d 4s 3p 3s 2p 2s 1s Know!! Figure 6.29 Goal: To write (ground state) e - configurations for atoms. Why? To represent the arrangement of e - s in atoms. How? Use the orbital energy diagrams, or better yet 7

8 Use the periodic table to write e - configs! Fig p 3d 4s 3p 3s 2p 2s Trends in e - configurations Noble-gas core abbreviations e - configs. and Periodic Table (lements in the same column have the same type of outer e - config.) Inner (core) e - s vs. outer (valence) e - s lements beyond Ca Write the e - config. of a. C b. O c. Na 1s Paired vs. unpaired e - s Filled and half-filled subshells Fig lectron Configurations 8