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Chemistry, The Central Science, 10th edition Theodore L. Brown; H. Eugene LeMay, Jr.; and Bruce E. Bursten Review Unit 1 (Chp 6,7): Atoms, Electrons, & Periodicity John D. Bookstaver St. Charles Community College St. Peters, MO 2006, Prentice Hall, Inc. Development of Atomic Models 1803 Dalton Atomic Theory 1904 Thomson Plum Pudding 1911 Rutherford Nuclear Model + Isotopes element: same or different mass: same or different why? same # of protons (& electrons), but different # of neutrons 1 H 1 protium 2 H 1 deuterium 3 H 1 tritium Average Atomic Mass • average atomic mass: calculated as a weighted average of isotopes by their relative abundances. • lithium-6 (6.015 amu), which has a relative abundance of 7.50%, and • lithium-7 (7.016 amu), which has a relative abundance of 92.5%. (6.015)(0.0750) + (7.016)(0.925) = 6.94 amu Avg. Mass = (Mass1)(%) + (Mass2)(%) … Mass Spectrometry isotopes separated by difference in mass Development of Atomic Models 1803 Dalton Atomic Theory 1904 Thomson Plum Pudding 1911 Rutherford Nuclear Model 1913 Bohr Shell Model 1926 Quantum Mechanical Model + What evidence ? 5.3 Atomic Emission Spectra • elements give discrete lines of E & f. (only specific colors of energy & frequency) Bohr’s Shell Model (1913–Niels Bohr) electrons occupy only specific levels (or shells) of “quantized” energy (& wavelength & frequency) Electrons as Waves quantized into specific multiples of wavelengths, but none in between. Bohr’s Shell Model EXCITED state e–’s absorb (+) energy, move to outer levels (n=2 to n=5) 5 2 ∆E e–’s emit (–) energy, move back to inner levels (n=5 to n=2) GROUND state 4 2 3 2 Which transition shows a light wave of the greatest energy? n=5 to n=2 R O Y G B I V Electromagnetic Spectrum Lowest Energy Highest Energy (higher ) (shorter ) • All EM radiation travels at the speed of light (c), 2.998 108 m/s. c = E = h (of 1 photon) Aufbau: Fill lowest energy orbitals first. 1s2 2s2 2p6 3s2 3p6 4s2 3d104p2 Hund: 1 e– in equal orbitals before pairing () (3d fills after 4s) ? Pauli Exclusion: no e–’s same props (opp. spin) (↑↓) nucleus + • Paramagnetic: species are attracted by a magnet (caused by unpaired electrons). Fe: [Ar] ↑↓ ↑↓ ↑ ↑ ↑ ↑ 4s 3d • Diamagnetic: species are slightly repelled by magnets (caused by all paired electrons) Zn: [Ar] ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ 4s 3d • d block metals lose their outer s electrons before any core d electrons to form ions. Fe 1s2 2s2 2p6 3s2 3p6 4s2 3d6 Fe2+ 1s2 2s2 2p6 3s2 3p6 3d6 Fe3+ 1s2 2s2 2p6 3s2 3p6 3d5 • d block (trans. metals) have colored ions due to light excited e– movement in d orbitals Other Aspects List 3 species isoelectronic with Ca2+ & S2–. P3– , Cl– , Ar, K+ , Sc3+ , Ti4+, V5+, Cr6+, Mn7+ Arrange the following species by increasing size: Ar, K+, Ca2+, S2–, Cl– Ca2+ < K+ < Ar < Cl– < S2– Spectroscopy SPECTROSCOPIC TECHNIQUE Microwave IR EM REGION Molecular Structure by Microwave molecular Rotation Infrared Vis/UV Atomic Emission Spectra Visible & (lines of frequencies/colors) PES (Photoelectron Spectroscopy) APPLICATION Ultraviolet X-ray Types of bonds by bond Vibration Transition of e–’s between energy levels Ionization of e–’s shows e– configuration WATCH this 6 min Video Explanation of PES at HOME. Relative # of e–’s Photoelectron Spectroscopy (PES) Which peak is H and which is He? higher peak = more e–’s 1s2 He 1s1 H 6 5 4 3 2 1 0 Binding Energy ...or Ionization Energy (MJ/mol) (required to remove e–’s) further left = more energy required (stronger attraction due to more protons) Relative # of e–’s Photoelectron Spectroscopy (PES) Which peak is H and which is He? 6 2p – Ne ? higher peak = more e ’s 1s2 Identify the 1 He 1s 2 1s2 2s element H & e-config 6 5 4 3 2 1 0 Binding Energy ...or Ionization Energy (MJ/mol) (required to remove e–’s) further left = more energy required (stronger attraction due to more protons) PES (A) Identify element (A) Ge WS #1,5 Identify element (B) K 3d10 2p6 1s2 n=1 2s2 n=2 3p6 3s2 n=3 4s2 4p2 n=4 PES (B) 4s1 ? Chemistry, The Central Science, 10th edition Theodore L. Brown; H. Eugene LeMay, Jr.; and Bruce E. Bursten Review Unit 1 (Chp 7): Periodicity …or… Periodic Trends in Atomic Properties John D. Bookstaver St. Charles Community College St. Peters, MO 2006, Prentice Hall, Inc. Periodic Trends • We will explain observed trends in size Atomic (and Ionic) Radius lose e– Ionization energy attract e– Electronegativity Zeff & shielding (explains all periodic trends and properties) Zeff & Shielding • effective nuclear charge, (Zeff): Zeff = Z − S Z = nuclear charge (+proton’s) S = shielding (core e–’s) attraction • shielding, (S): shielding inner core e–’s shield valence Zeff e–’s from nuclear attraction. Z = +11 +11 Na atom Zeff = +1 Atomic Radius decreases across a period -due to increasing Zeff (more protons) att. =shield Zeff increases down a group -due to increasing shielding (more energy levels) att. shield =Zeff Ionic Radius Why? • Cations are • Anions are smaller than atoms. larger than atoms. loses a shell core shell closer to nucleus new valence e– ‘s less shielded (greater Zeff) electrons are added and repulsions are increased (same Zeff & same shielding) Ionization Energy (IE) • • • • energy required to remove an electron more energy to remove each electron IE1 < IE2 < IE3, … look for a huge jump in IE once all valence e–’s are removed, the next e– is on an inner level with attraction (shielding & Zeff). huge jump in IE4 b/c 4th e– on inner level (must have 3 valence e–’s) Trends in First IE IE tends to… increases across a period decreases down a group -due to increasing Zeff (more protons) att. =shield Zeff -due to increasing shielding (more energy levels) att. shield =Zeff Trends in Electronegativity (EN) decreases down a group -ability of an atom to attract electrons when bonded with another atom. increases across a period -greater Zeff -more shielding (more energy levels) Periodic Trends (Summary) Electronegativity Can you explain all of this in terms of p’s and e’s? Electronegativity Zeff & shielding WS #2,3 Atomic radius