Chapter 11 Modern Atomic Theory

Copyright © Houghton Mifflin Company. All rights reserved. 11 | 2 Rutherford’s Atom The concept of a nuclear atom (charged electrons moving around the nucleus) resulted from Ernest Rutherford’s experiments. Question left unanswered: how are electrons arranged and how do they move?

Copyright © Houghton Mifflin Company. All rights reserved. 11 | 3 Rutherford’s Atom (cont.)

Copyright © Houghton Mifflin Company. All rights reserved. 11 | 4 Electromagnetic Radiation Electromagnetic radiation is given off by atoms when they have been excited by any form of energy, as shown in flame tests. Flame tests: Sample:Color: LiCl SrCl 2 NaCl KCl CaCl 2

Copyright © Houghton Mifflin Company. All rights reserved. 11 | 5 Electromagnetic Waves Velocity = c = speed of light – x 10 8 m/s –All types of light energy travel at the same speed. Amplitude = A = measure of the intensity of the wave, i.e.“brightness”

Copyright © Houghton Mifflin Company. All rights reserved. 11 | 6 Electromagnetic Waves (cont.) Wavelength =  = distance between two consecutive peaks or troughs in a wave –Generally measured in nanometers (1 nm = m) –Same distance for troughs Frequency = = the number of waves that pass a point in space in one second –Generally measured in Hertz (Hz), –1 Hz = 1 wave/sec = 1 sec -1 c = x

Copyright © Houghton Mifflin Company. All rights reserved. 11 | 7 Types of Electromagnetic Radiation

Copyright © Houghton Mifflin Company. All rights reserved. 11 | 8 Planck’s Discovery Showed that for certain applications light energy could be thought of as particles or photons

Copyright © Houghton Mifflin Company. All rights reserved. 11 | 9 Emission of Energy by Atoms/Atomic Spectra Atoms that have gained extra energy release that energy in the form of light.

Copyright © Houghton Mifflin Company. All rights reserved. 11 | 10 Atomic Spectra Line spectrum: very specific wavelengths of light that atoms give off or gain Each element has its own line spectrum, which can be used to identify that element. This is the basis of atomic absorption spectroscopy.

Copyright © Houghton Mifflin Company. All rights reserved. 11 | 11 Atomic Spectra (cont.) Hydrogen atoms have several excited state energy levels. Different colors are produced when the excited atoms return to the ground state. The line spectrum of hydrogen must be related to energy changes in the atom.

Copyright © Houghton Mifflin Company. All rights reserved. 11 | 12 Atomic Spectra (cont.) The atom is quantized, i.e. only certain energies are allowed. Continuous levels Quantized levels

Copyright © Houghton Mifflin Company. All rights reserved. 11 | 13 Bohr’s Model (Niel’s Bohr ) Energy of the atom is quantized –An atom can only have certain specific energy states called quantum levels or energy levels. –When an atom gains energy, an electron “moves” to a higher quantum level. –When an atom loses energy, the electron “moves” to a lower quantum level. –Lines in a spectrum correspond to the difference in energy between the levels.

Copyright © Houghton Mifflin Company. All rights reserved. 11 | 14 Bohr’s Model (cont.) Ground state: minimum energy of an atom The ground state of hydrogen corresponds to having its one electron in the n=1 level Excited states: energy levels higher than the ground state

Copyright © Houghton Mifflin Company. All rights reserved. 11 | 15 Bohr’s Model (cont.) Distances between energy levels decrease as the energy increases –1st energy level can hold 2 electrons, the 2nd level 8 electrons, the 3rd 18 electrons, etc.

Copyright © Houghton Mifflin Company. All rights reserved. 11 | 16 Problems with the Bohr Model Only explains hydrogen atom spectrum (and other 1-electron systems). Neglects interactions between electrons. Assumes circular or elliptical orbits for electrons (which is not true).

Copyright © Houghton Mifflin Company. All rights reserved. 11 | 17 Wave Mechanical Model of the Atom Experiments later showed that electrons could be treated as waves: Louis De Broglie The quantum mechanical model treats electrons as waves and uses wave mathematics to calculate probability densities of finding the electron in a particular region in the atom. –Schrödinger Wave Equation

Copyright © Houghton Mifflin Company. All rights reserved. 11 | 18 Orbitals and Energy Levels Solutions to the wave equation give regions in space of high probability for finding the electron. These are called orbitals. Each principal energy level contains one or more sublevels. Sublevels are made up of orbitals.

Copyright © Houghton Mifflin Company. All rights reserved. 11 | 19 Orbitals and Energy Levels (cont.)

Copyright © Houghton Mifflin Company. All rights reserved. 11 | 20 Atomic Sublevels & Orbitals Each type of sublevel has a different shape each and energy. s orbital shape: p orbital shapes: Each sublevel contains one or more orbitals.

Copyright © Houghton Mifflin Company. All rights reserved. 11 | 21 Atomic Sublevels & Orbitals (cont.)

Copyright © Houghton Mifflin Company. All rights reserved. 11 | 22 Pauli Exclusion Principle No orbital may have more than 2 electrons. Electrons in the same orbital must have opposite spins. s sublevel holds 2 electrons (1 orbital) p sublevel holds 6 electrons (3 orbitals) d sublevel holds 10 electrons (5 orbitals) f sublevel holds 14 electrons (7 orbitals)

Copyright © Houghton Mifflin Company. All rights reserved. 11 | 23 Sublevels and Orbitals n Sublevels : Types of Orbitals (and numbers) 11s(1) 22s(1)2p(3) 33s(1)3p(3)3d(5) 44s(1)4p(3)4d(5)4f(7) For a multiple-electron atom, build-up the energy levels, filling each orbital in succession from lowest to highest. Degenerate orbitals: orbitals with the same energy e.g. Each p sublevel has 3 degenerate p orbitals

Copyright © Houghton Mifflin Company. All rights reserved. 11 | 24 Orbital Filling 1s2s2p3s3p3d4s4p4d4f5s5p5d5f6s6p6d7s7p1s2s2p3s3p3d4s4p4d4f5s5p5d5f6s6p6d7s7p Therefore, the order of filling is:

Copyright © Houghton Mifflin Company. All rights reserved. 11 | 25 Electron Configurations For a set of degenerate orbitals, fill each orbital half-way first before pairing the electrons. Electron configurations show how many electrons are in each sublevel of an atom – describes where the electrons are. - The electron configuration for a ground state Li atom is: - The electron configuration for a ground state N atom is:

Copyright © Houghton Mifflin Company. All rights reserved. 11 | 26 Electron Configurations (cont) What is the electron configuation of: A.potassium B.cobalt

Copyright © Houghton Mifflin Company. All rights reserved. 11 | 27 Electron Configurations (cont.) Valence shell: highest energy level –Electrons in the valence shell are called valence electrons. –Core electrons: electrons not in the valence shell –Often use symbol of previous noble gas in brackets to represent core electrons: phosphorus: 1s 2 2s 2 2p 6 3s 2 3p 3 = corevalence

Copyright © Houghton Mifflin Company. All rights reserved. 11 | 28 Electron Configuration and the Periodic Table Elements in the same column on the periodic table have: –Similar chemical and physical properties –Similar valence shell electron configurations same numbers of valence electrons same orbital types, but different energy levels Be: Mg:

Copyright © Houghton Mifflin Company. All rights reserved. 11 | 29 s1s1 d 1 d 2 d 3 d 4 d 5 d 6 d 7 d 8 d 9 d 10 p 1 p 2 p 3 p 4 p 5 p6p6 f 1 f 2 f 3 f 4 f 5 f 6 f 7 f 8 f 9 f 10 f 11 f 12 f 13 f s2s2

Copyright © Houghton Mifflin Company. All rights reserved. 11 | 30

Copyright © Houghton Mifflin Company. All rights reserved. 11 | 31 Orbital diagrams Orbital diagrams (or box diagrams) show orbitals as boxes grouped by sublevels with arrows representing the electrons. Sulfur has an electron configuration of : The orbital diagram for sulfur is:

Copyright © Houghton Mifflin Company. All rights reserved. 11 | 32 Atomic Properties and the Periodic Table

Copyright © Houghton Mifflin Company. All rights reserved. 11 | 33 Metallic Character: Metals Metals –Malleable & ductile –Shiny, lustrous –Conduct heat and electricity –Form cations in solution –Lose electrons in reactions - oxidized

Copyright © Houghton Mifflin Company. All rights reserved. 11 | 34 Metallic Character: Metalloids Metalloids -Also known as semi-metals -Show some metal and some nonmetal properties

Copyright © Houghton Mifflin Company. All rights reserved. 11 | 35 Metallic Character: Nonmetals Nonmetals -Brittle in solid state -Form anions and polyatomic anions -Gain electrons in reactions - reduced

Copyright © Houghton Mifflin Company. All rights reserved. 11 | 36 Metallic Character (cont.) The ease of losing an electron varies as follows: Cs > Rb > K > Na > Li The same trend is seen in the Group 2 metals:

Copyright © Houghton Mifflin Company. All rights reserved. 11 | 37 Trend in Ionization Energy Minimum energy needed to remove a valence electron from an atom in the gas phase: M(g) → M + (g)+ 1e - The lower the ionization energy, the easier it is to remove the electron. –Metals in general have low ionization energies and nonmetals relatively high ones. Ionization energy decreases down the group. –Valence electron is farther from the nucleus Ionization energy increases left to right across the period.

Copyright © Houghton Mifflin Company. All rights reserved. 11 | 38 Trend in Atomic Size