A Conceptual Introduction to Chemistry, First Edition

Chapter 4Electron Structure of the Atom1Review of Atomic StructureThe center of the atom is called the nucleus. In it are the particles with mass: the protons and neutronsProtons determine the identity of an atomElectrons determine the properties of an atomWhere are the electrons? 2LightWhat is light, and what does it have to do with the electrons in an atom?Light is electromagnetic radiation.

3Electromagnetic Radiation (EMR)Form of energy with wavelike behavior as it travels through space at the speed of light Seven major types:Gamma () RaysX raysUltraviolet (UV)Visible Light (ROYGBIV)Infrared (IR)MicrowavesRadio waves45Electromagnetic Spectrum(p. 98)

5Wavelength ()The distance between two corresponding points on a waveUnits are same as length - m, or commonly nm (10-9 m)Figure 7.5

6Know the wavelengths for the visible spectrumR O Y G B IV700 650 600 550 500 450 400 nmFrequency number of wave cycles that move through a point in space in 1 shertz (Hz)same as inverse seconds (1/s) or (s-1)

8Which has the greater wavelength the red light or the green light?Which has a greater frequency?

Figure 7.7

9Frequency & Wavelengthinversely proportionali.e. as one increases the other decreases

c =

c = speed of light (3.00 x 108 m/s) = wavelength (in meters) = frequency (in Hz)

10PracticeWhat is the frequency and wave type of a wave with a wavelength of 5.2 x 10-7 m (5.2 x 102 nm)?wave type: green visible light

11

PracticeWhat is the frequency and wave type of a wave with a wavelength of 5.2 x 10-7 m (5.2 x 102 nm)?wave type: green visible light12What is the approximate frequency of blue light?

Wavelength = 475nm

R O Y G B IV400

70013Convert nm to m

R O Y G B IV400

700

What is the approximate frequency of blue light?

R O Y G B IV400

70015HomeworkCalculate the frequency of light with a wavelength of 3.41 x 103 cm?Calculate the wavelength of light with a frequency of 3.21 x 1016 Hz? What type of EMR is it?What is the frequency of orange light?Line SpectraContinuous spectrumall the wavelength of in the visible spectrumProduced by white lightLine Spectrumdistinct colored lineseach a single wavelength of lightVisible when an element has been heated atomic fingerprint

17Energy is Quantized!Quantized = quantity = specific measured amount

Max Planck energy produced by atoms can only have certain values only distinct lines are seen in element line spectracan only exist at certain wavelengths. 18Max PlanckProposed that objects emit energy in small packets called quantaQuantum: min. quantity of energy lost or gained by an atomThis quantized energy is related to the frequency of the energy19Photons waves and particlesEnergy of a photondirectly proportional to the frequency

Ephoton = h

inversely proportional to the wavelength

Ephoton = hc/l

Ephoton = (in Joules)

h = Plancks constant (6.626 x 10-34 Js) = frequency (in Hz) l = wavelength in meters

20

LowHigh Low E

High LowHigh E

PracticeWhat is the energy of a photon with a frequency of 1.000x1017Hz? 22

PracticeWhat is the energy of a photon with a wavelength of 8.1m?

23Atomic SpectraWhen visible light passes through a prism, its components separate into a spectrum.White light, such as sun light or light from a regular light bulb, gives a continuous spectrum:

24Photoelectric EffectEmission of electrons from a metal when light shines on it

25This was explained by EinsteinBased on Planck's work, Einstein proposed that light also delivers its energy in chunks; light would then consist of little particles, or quanta, called photons, each with an energy of Planck's constant times its frequency Electrons are only emitted if the photons have a high enough energy (high enough frequency)2627Atomic SpectraColored light gives only specific colors in a line spectrum:

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What does this have to do with electrons?Hydrogen atom: 1 proton, 1 electronPassing electricity through a tube containing hydrogen gas gives off a pink lightLight is given off as electrons fall from an excited state to a ground stateThe light can be separated into four frequencies28Spectra of other elements(spectral signatures applet)29Energy Level Transition

Excited State: higher energy state

Ground State: lowest energy state

EphotonEphoton= Eexcited- Eground=h30Bohr Model links electron and emissionsNiels Bohr (Danish physicist)planetary modelelectron are in orbits orbit 1 closest to the nucleus increasing numbers as the orbits get further away from the nucleus.

31Bohr ModelOrbits have a fixed radius.Electrons cannot exist between orbitslowest energy is closest to the nucleusincreases as the orbits get further away Electrons absorb or emit energy when they change orbitalsE = Ef Ei

32Deficiencies of Bohr ModelDid not work for other atomsDoesnt explain chemical behavior of atomsMore complex model needed

However, the Bohr model did give insight into the quantized behavior of the atom that was better understood in later days33Modern Models of the AtomBohrdeBroglieSchrdinger (Wave Mechanical Model)

To view at home, click here. Click on Run Now!35Modern Model of the Atom(Quantum Mechanical Model)electrons exist in orbitals.Orbitals are 3-dimensional regions in space where an electron is likely to be foundnot a circular pathwayThe electron is thought of having wave properties

3536The exact location of the electron cannot be known. (Heisenberg Uncertainty Principle)The location is described as a probabilityThis is a Probability Map for lowest-energy state of the electron in an H atom

36A typical representation of an s-orbital

3738Principal Energy LevelsOrbitals of similar size exist in the same principal energy level (n=1, 2, 3)The principal energy levels correspond to Bohrs energy levels and represent a distance from the nucleus

3839Energy levels contain orbitalsLower energy orbitals are smaller.Higher energy orbitals are larger; further away from the nucleus.An orbital can hold at most 2 electrons.

39SublevelsOrbitals are arranged in sublevels, which have specific shapes s, p, d, and f are sublevels

s p d f

40s Orbitals Figure 7.14

41p Orbitals

42d Orbitals

4344f Orbitals

44Memorize terms!Principal Energy level: distance from nucleusSublevel: series of orbitals having equal energyOrbital: particular region where an electron exists

Orbitals make up sublevels, and sublevels make up energy levels

What each energy level holds(Table 2, p. 110)The first energy level (n=1)A single s orbitalThe second energy level (n=2)2s orbital and 2p sublevel (three 2p orbitals)The third energy level (n=3)3s orbital, 3p sublevel (three 3p orbitals) and 3d sublevel (five 3d orbitals)The fourth energy level (n=4)4s orbital, 4p sublevel, 4d sublevel and 4f sublevel (seven 4f orbitals)46

Hydrogen Orbital DiagramAufbau Orbital diagramsShow the sublevels and orbitals that can exist at each principal energy levelEach box represents an orbitalGroups of boxes represent sublevelsIn the hydrogen atom only, the sublevels within a principal energy level all have the same energy.

49Multielectron Orbital DiagramIn the multielectron atoms, the sublevels within a principal energy level have different energy levels.

50Orbital Diagram RulesAufbau principleElectrons fill orbitals starting with the lowest-energy orbitals.Pauli exclusion principleA maximum of two electrons can occupy each orbital, and they must have opposite spins.Hunds rule Electrons are distributed into orbitals of identical energy (same sublevel) in such a way as to give the maximum number of unpaired electrons.Electrons are always filled in their ground state, or lowest energy state.51Hydrogens Orbital Diagram

1 electron52Heliums Orbital Diagram

53Lithiums Orbital Diagram

54Borons Orbital Diagram

55Carbons Orbital Diagram Pg. 251 (Carbons orbital diagram)

56Filling Orbital DiagramsWhy do the electrons in the p sublevel occupy separate orbitals?It takes a little bit of energy to pair up electrons, so single electrons occupy different orbitals with the same energy (Hunds Rule)

57Orbital Diagrams for the 1st Ten Elements

58Electron ConfigurationsAn electron configuration is a shorthand notation for representing the number of electrons in each sublevelCarbon has 6 electrons.

Therefore, using the orbital diagram we obtain:1s22s22p2

5960

60Order of Fill

Periodicity of Electron ConfigurationsCan you tell the patterns among the following groups of elements?Alkali Metals (Group IA)Li1s22s1Na1s22s22p63s1Alkali Earth Metals (Group IIA)Mg1s22s22p63s2Ca1s22s22p63s23p64s2Halogens (Group VIIA)Cl1s22s22p63s23p5Br1s22s22p63s23p64s23d104p5Noble Gases (Group VIIIA)Ne1s22s22p6Ar1s22s22p63s23p5 62Using the Periodic Table for Electron ConfigurationsBlocks contain elements with the same highest-energy sublevel.

63Periodicity of Electron ConfigurationsNotice the number of columns in the s, p, d and f blocks is the same as the number of electrons allowed in each sublevel

64Periodicity of Electron ConfigurationsThe principal energy level number, the number that comes before the sublevel letter designation, is the same as the period number for the s and p sublevels.For the d sublevels, the principal energy level number is one less than the periodic number.6566The Principal Quantum Number and Sublevel on the Periodic Table Figure 7.21

66An Example of Electron ConfigurationP: 1s22s22p63s23p3 Mn: 1s22s22p63s23p64s23d5

67Abbreviated Electron ConfigurationNotice that phosphorus electron configuration starts out with neons electron configurationPhosphorus 1s22s22p63s23p3Neon 1s22s22p6We use the symbol for Neon to represent neons electron configuration in the configuration for phosphorus.

The abbreviated electron configuration for P would be:[Ne] 3s23p3 68The outermost electrons are often shown in this way:[Ar] 4s23d10 4p4

The most important electrons are the ones with the highest number, or energy level

69Valence ElectronsThe electrons on the outside edge of the atom This is where the action is- where bonding takes placeAtoms have no more than 8 valence electrons

NeonArgon

Radon70Energy Level (Shell)Maximum Number of ElectronsMax number of Valence Electrons1222883188432855086728798871The Octet Rule:Atoms will combine to form compounds in order to reach eight electrons in their outer energy level. Atoms with less than 4 electrons tend to lose electrons.Atoms with more than 4 electrons tend to gain electrons.

72Electron-dot diagrams can be used to give the number of valence electronsThe number of valence electrons is equal to the element group number 1A 2A 3A 4A 5A 6A 7A 8A

73

iodine

phosphorus

gallium

argon

Write the electron-dot symbols for the following elements:

74Valence Electrons, reviewThe highest principal energy level is called the valence level, or valence shellThe valence level contains electrons that are furthest from the nucleus (on the outside edge) and highest in energyInner-level electrons are called core electronsValence electrons are important in chemical reactions75