Atomic Structure

Atomic Structure

Atomic Structure 1 Discovery and Properties of Electrons Humphrey Davy (early 1800s) passed electricity through compounds compounds decomposed into elements compounds are held together by electrical forces Michael Faraday - (1832-1833) amount of reaction that occurs during electrolysis is proportional to current passed through compounds 2

Discovery of the Electron J.J. Thomson proved the existence of the electron by showing that the beam in the Crookes tube experiments could be deflected when passed between two plates containing opposite charges. 3 Discovery of the Electron Electrons carry the - charge since they come from the negative electrode and go to the positive electrode. 4 Discovery of the Electron

J.J. Thomson determined the e/m ratio by measuring the degree of deflection of cathode rays. e/m = 1.75882 x 108 coulomb/g 5 Millikan Oil-Drop Experiment Determined the charge electron. -1.60218 x 1019C/e 6 Electron Mass Millikans determination of the charge of an electron allowed for the determination of the mass of an electron.

1g 19 m x 1 . 60218 x 10 C 8 1.75882x10 C m 9.10940x10 28 g / electron 7 Discovery of Proton

Rutherford shot -particles at thin gold (Au) foil to see if they would be deflected. Some -particles were deflected back. This could happen only if a highly concentrated + charge was deflecting the positively charged -particle. 8 Rutherford Model of the Atom Atoms consist of very small, very dense nuclei surrounded by clouds of electrons at relatively great distances from

the nuclei. 9 Atomic Theory All nuclei contain protons. Protons have a positive charge. analyzed evidence from -particle scattering recognized existence of massive neutral particles - neutrons James Chadwick-1932

10 Mass Number & Isotopes H.G. J. Moseley (1912-1914) recognized that atomic number is the defining difference between elements new understanding of Mendeleevs periodic law 11 Atomic Theory All atoms, except for hydrogen, also contain

neutrons. Neutrons do not have a charge. 12 Atom Composition The atom is mostly empty space protons and neutrons in the number of electrons is equal to the number of protons. electrons in space around the nucleus. extremely small.

the nucleus. One teaspoon of water has 3 times as many atoms as the Atlantic Ocean has teaspoons of water. 13 Structure of the Atom Composed of: protons neutrons electrons protons found in nucleus relative charge of +1 relative mass of 1.0073 amu

Structure of the Atom Composed of: protons neutrons electrons neutrons found in nucleus neutral charge relative mass of 1.0087 amu Structure of the Atom Composed of: protons neutrons electrons

electrons found in electron cloud relative charge of -1 relative mass of 0.00055 amu How Large is an Atom? Scanning Tunneling Microscopic images of carbon atoms in graphite. 17

Isotopes Two or more forms of atoms of the same element with different masses. Atoms contain the same number of protons but different numbers of neutrons. Boron-10 (10B) has 5 p and 5 n 11 B Boron-11 (11B) has 5 p and 6 n 10 B 18 Isotopes of Hydrogen Symbol Nuclide Protons Neutrons H 1

D 2 T 3 Electrons H 1 0 1 H 1 1

1 H 1 2 1 1 1 1 19 Mass Number Mass Number: total number of protons + neutrons (nucleons) in an atom. Mass Number = # protons + # neutrons

mass number = 6 p + 6 n = 12 amu C 12 12 6 number of protons Carbon-12, 6C 20 Isotopes of Carbon # Neutrons = Mass Number - # Protons 12 6 C 13 6 C

14 6 C 6 protons 6 protons 6 protons 12 - 6 = 6 13 - 6 = 7 14 - 6 =8 6 neutrons 7 neutron 8 neutrons 21 31P 15 Example Consider a neutral atom of the element phosphorus:

Atoms of this element have how 15 many protons in their nucleus? How many electrons does a neutral atom of phosphorus have? 15 How many neutrons does an atom of phosphorus have in its nucleus? 16 22 40Ca 20 Example

Consider a neutral atom of the element Calcium: Atoms of this element have how 20 many protons in their nucleus? How many electrons does a neutral atom of calcium have? 20 How many neutrons does an atom of calcium have in its nucleus? 20 23 40Ca2+ 20 Example

Consider a neutral atom of the element Calcium: Atoms of this element have how many protons in their nucleus? 20 How many electrons does a neutral atom of calcium have? 18 How many neutrons does an atom of calcium have in its nucleus? 20 24 Atomic Weight

One amu is exactly 1/12 of the mass of a 12C atom. 12C is a specific isotope of carbon. 1 g = 6.022 x 1023 amu 25 Atomic Weight The weighted average of the masses of its constituent isotopes. [( Atomic = Weight ) x( fractional abundance

)] isotopic mass AW fraction1 x AW1 fraction2 x AW2 ... 26 Mass Spectrometer Neon Increased Deflection The natural relative abundances for different isotopes can be determined from the mass spectrum. 27 Carbon is listed as have an atomic weight of 12.01 amu in the periodic table, based on the weighted average of all carbon isotopes... isotope

abundance mass amu neutrons 12 C 98.89% 12.0000 6 13 C 1.11% 13.0034 7 14 C

< .01% 8 n/a 28 The atomic weight of carbon is 12.011 amu, computed as follows... Atomic weight of C = the sum of (%abundance of isotope) x (its mass) for all stable isotopes. So... as percentages (98.89%)(12 amu) + (1.11%)(13.0034 amu) = or as fractions (0.9889)(12 amu) + (0.111)(13.0034 amu) =

12.011 amu 29 Mass Spectrometer Neon Atomic weight of Ne = (90.48%)19.9924 amu +(0.27%)20.9938 amu + (9.25%)21.9914 amu = (0.9048)*19.9924 amu +(0.0027)*20.9938 amu + (0.0925)*21.9914 amu = 20.1797 amu 30 Atomic Weight What is the average atomic weight of Mg? AW = 0.7899(23.98504) + 0.1000(24.98584) + 0.1101(25.98259) 24.30 amu Mg-24 Mg-25 Mg-26

78.99% 10.00% 11.01% 23.98504 24.98584 25.98259 31 Atomic Weight The atomic weight of Ga is 69.72; Ga-69 = 68.9257; Ga-71 = 70.9249 What is the abundance of each isotope? 32 Atomic Weight

Let x = abundance Ga-69 1-x = abundance of Ga-71 x(68.9257) + (1-x)(70.9249) = 69.72 68.9257x + 70.9249 70.9249x = 69.72 1.9992x = 1.20 x = 0.600 Ga-69 = 60.0% and Ga-71 = 40.0% 33 Electromagnetic Spectrum Visible light makes up only a small part of the electromagnetic spectrum. 34 Electromagnetic Spectrum Electromagnetic radiation has a dual behavior.

It has properties of a particle called a photon and as a wave traveling at the speed of light. Characterized by a wavelength and frequency. 35 Electromagnetic Radiation Wavelength- The distance between two corresponding points on a wave. 36 Electromagnetic Radiation Frequency- The number of wave crests passing a given point per unit time. 37

Electromagnetic Radiation c = c = 3.00 x 108 m/s 38 Electromagnetic Radiation Note that long wavelength small frequency Short wavelength high frequency QuickTime and a Graphics decompressor are needed to see this picture. increasing frequency increasing wavelengt 39 Electromagnetic Radiation

= Given = 7.31 x 1014s-1, calculate 3.00 x 108 m / s 14 1 = 7.31 x 10 s 4.10 x 10-7 m 9 1 x 10 nm = 410 nm nm = 4.10 x 10-7 m x m

40 Plancks Equation hc E h E = energy of 1 photon h = Plancks constant, 6.626 x 10-34 J-s = frequency, s-1 = wavelength, m c = speed of light, 3.00 x 108 m/s 41 Quantization of Energy E = h Light with large (small ) has a small E. Light with a short (large ) has a large E. 42

Quantization of Energy E = h 43 Plancks Equation Calculate the energy of a photon with a wavelength of 4.10 x 10-7m. 34 8 6 . 63 x 10

J s 3 . 00 x 10 m/s hc E 4.10 x 10 7 m E = 4.85 x 10-19 J 44 Quantum Theory

Allowed for the interpretation of spectra of atoms, ions, and molecules. Neils Bohr proposed the fundamental hypothesis of the quantum theory. 45 Atomic Line Spectra and Niels Bohr Niels Bohr (18851962) Bohrs greatest contribution to science was in building a simple model of the atom. It

was based on an understanding of the SHARP LINE SPECTRA of excited atoms. 46 Line Spectra of Excited Atoms Excited atoms emit light of only certain wavelengths The wavelengths of emitted light depend on the element. 47 Line Spectra of Excited Atoms High E

Short High Visible lines in H atom spectrum are called the BALMER Low series. E Long Low 48 Bohr Model of Atom An atom has a number of definite and discrete energy levels in which an electron can exist.

Increasing radius of orbit increases the energy. Electrons can move from one energy level to another. Electron moves in circular orbit. 49 The Bohr Model and Quantized Energy Excited State Electron Energies Energies are are quantized quantized in in other other words words the the Energies Energies are

are limited limited to to discrete discrete values. values. e+ e- High High Energy Energy Orbit Orbit Low Low Energy Energy Orbit Orbit Ground Ground State

State Energy Energy 50 Atomic Spectra Atomic spectra tells us about the structure of the atom. 51 Atomic Spectra Continuous spectra from sun contain all wavelengths. Line spectra have discrete lines from atoms. 52 Atomic Spectra

Emission The process where an electron moves from a higher to lower energy state, resulting with the loss of energy. 53 Atomic Spectra Absorption The process where an electron moves from a lower to higher energy state, resulting with the gain of energy. 54 Spectral Lines Second Electronic Excited States

E N E R G Y First Electronic Excited States Ground Electronic Excited States 55 Hydrogen Atom Only certain lines are found in the atomic spectrum of hydrogen. Bohr: electron can only have

certain energy values. Balmer: expressed relationship mathematically. 56 Rydberg Equation 1 1 E RH 2 2 ni nf RH = 2.18 x 10-18 J ni = initial value of n nf = final value of n 57 Rydberg Equation What wavelength of light is associated with a transition from n 1 = 4 to n 18= 2?

1 19 E 218 . x 10 J 2 2 4.09 x 10 2 4 hc 6.63 x 10 34 J s 3.00 x 108 m / s E 4.09 x 10 19 J J

= 4.86 x 10-7 m = 486 nm 58 Atomic Line Spectra and Niels Bohr Niels Bohr (18851962) Bohrs theory was a great accomplishment. Recd Nobel Prize, 1922 Problems with theory theory only successful for H. introduced quantum idea artificially. So, we go on to QUANTUM or WAVE MECHANICS 59 Quantum or Wave

Mechanics de Broglie (1924) proposed that all moving objects have wave properties. L. de Broglie (1892-1987) = h/mv 60 Quantum or Wave Mechanics Baseball (115 g) at 100 mph = 1.3 x 10-32 cm Experimental proof of wave properties of electrons electron with velocity = 1.9 x 108 cm/sec

= 0.388 nm 61 Wave Nature of Electron Calculate the wavelength of an electron traveling at 1.243 x 107m/ s. 2 2 . x 10 663 34 1kg m / s J s J

h m 911 . x 10 31 kg 1243 . x 107 m / s 11 587 . x 10 m Which is similar to the spacing between atoms in 62 Quantum Mechanical Picture Werner Heisenberg - 1927

Uncertainty Principle It is impossible to determine simultaneously both the position & momentum of an electron. electron microscopes use this phenomenon 63 Quantum Mechanical Picture Werner Heisenberg may have slept here! 64 Quantum Mechanical Picture

devices for detecting motion of electron disturbs its position like measuring position of a car with a wrecking ball 65 Quantum Mechanical Picture

Schrdinger proposed an equation that contains both wave and particle terms. Solving the equation leads to wave functions. The wave function gives the shape of the electronic orbital. The square of the wave function, gives the probability of finding the electron, that is, gives the electron density for the atom. WAVE FUNCTION 66 Orbitals and Quantum Numbers If we solve the Schrdinger equation, we get wave functions and energies for the wave functions.

We call wave functions orbitals. Schrdingers equation requires 3 quantum numbers: Principal Quantum Number, n. This is the same as Bohrs n. As n becomes larger, the atom becomes larger and the electron is further from the nucleus. 67 Quantum Theory Atoms have discrete energy states. Atoms have definite energy. Changes in energy results in absorption or emission of energy. Allowed energy states are

described by quantum numbers. 68 Quantum Numbers Principal quantum number-n main energy level n = 1, 2, 3, ... 69 Quantum Numbers Subsidiary quantum number-l shape of orbital l = 0, 1, 2, ... n-1

l l l l = = = = 0 s orbital 1 p orbital 2 d orbital 3 f orbital 70 Atomic Orbitals s orbitals

71 Atomic Orbitals p orbitals 72 Atomic Orbitals d orbitals 73 Atomic Orbitals f orbitals 74

Quantum Numbers Magnetic quantum number-ml spatial (xyz) orientation of orbital -l, -1, 0, 1, 2 ..., l l l l l = = = = 0 s orbital 1 p orbital

2 d orbital 3 f orbital ml ml ml ml = = = = 0 -1, 0, 1 -2, -1, 0, 1, 2 -3, -2, -1, 0, 1, 2, 3 75 Atomic Orbitals

There are three p-orbitals px, py, and pz. (The three p-orbitals lie along the x-, yand z- axes of a Cartesian system. The letters correspond to allowed values of ml of -1, 0, and +1.) The orbitals are dumbbell shaped. As n increases, the p-orbitals get larger. All p-orbitals have a node at the nucleus. 76 The p Orbitals 77 The d and f Orbitals

There are 5 d- and 7 f-orbitals. Three of the d-orbitals lie in a plane bisecting the x-, y- and z-axes. Two of the d-orbitals lie in a plane aligned along the x-, y- and z-axes. Four of the d-orbitals have four lobes each. d xy , d yz , d xz , d x -y , d z One d-orbital has two lobes and a collar. 2 2 2 78 The d Orbitals 79 Atomic Orbitals

f orbitals start with n = 4 most complex shaped orbitals 7 per n level, complicated names l=3 ml = -3,-2,-1,0,+1,+2, +3 7 values of ml important effects in lanthanides & actinides 80 Quantum Numbers

Spin quantum number-ms + or - Wolfgang Pauli - 1925 exclusion principle no two electrons in an atom can have the same set of 4 quantum numbers. 81 Pauli Exclusion Principle

No two electrons in an atom can have the same set of four quantum numbers. No two electrons with the same spin in an atom can fill one orbital. 82 Quantum Numbers 1 2 3 4 5 6 7 Write quantum numbers for each

electron in nitrogen. n 1 1 2 2 2 2 2 l 0 0 0 0 1 1 1 ml 0 0 0 0

-1 0 1 ms - - 83 Quantum Numbers What are the values for n and l for: n 1s 4d

3p 4f l 1 4 3 0 2 4 3 1 84 Aufbau Principle The electron that distinguishes an element from the previous element

enters the lowest-energy atomic orbital available 85 Energy Levels The order of filling is determined by the energy of each orbital. 86 s electrons p electrons IA 1 H 1.008

3 Li 6.941 11 Na 22.99 19 K 39.1 37 Rb 85.47 55 Cs 132.9 87 Fr (223) d electrons IIA IIIA

4 Be 9.012 12 Mg 24.31 20 Ca 40.08 38 Sr 87.62 56 Ba 137.3 88 Ra 226 5 IIIB 21

Sc 44.96 39 Y 88.91 57 La 138.9 89 Ac 227 IVB 22 Ti 47.88 40 Zr 91.22 72 Hf 178.5 VB

23 V 50.94 41 Nb 92.91 73 Ta 180.9 VIB 24 Cr 52 42 Mo 95.94 74 W 183.9 VIIB 25 Mn

54.94 43 Tc -98 75 Re 186.2 26 Fe 55.85 44 Ru 101.1 76 Os 190.2 VIIIB 27 Co 58.93 45 Rh

102.9 77 Ir 192.2 B 10.81 13 Al IB IIB 26.98 28 29 30 31 Ni Cu Zn Ga 58.69 63.55 65.39 69.72 46 47 48 49

Pd Ag Cd In 106.4 107.9 112.4 114.8 78 79 80 81 Pt Au Hg Tl 195.1 197 200.6 204.4 IVA 6 C 12.01 14 Si 28.09 32 Ge

72.61 50 Sn 118.7 82 Pb 207.2 VA 7 N 14.01 15 P 30.97 33 As 74.92 51 Sb 121.8 83 Bi 209

VIA 8 O 15.99 16 S 32.07 34 Se 78.96 52 Te 127.6 VIIA 9 F 19 17 Cl 35.45 35 Br

79.9 53 I 126.9 85 Po At (209) (210) VIIIA 2 He 4.003 10 Ne 20.18 18 Ar 39.94 36 Kr 83.8 54 Xe

131.3 86 Rn (222) f electrons 58 59 60 61 Ce Pr Nd Pm 140.1 140.9 144.2 (145) 90 91 92 93 Th Pa U Np 232 231 238 237

62 63 Sm Eu 150.4 152 94 95 Pu Am (244) (243) 64 Gd 157.3 96 Cm (247) 65 Tb 158.9 97 Bk

(247) 66 Dy 162.5 98 Cf (251) 67 Ho 164.9 99 Es (252) 68 Er 167.3 100 Fm (257) 69

70 71 Tm Yb Lu 168.9 173 175 101 102 103 Md No Lr (258) (259) (260) 87 Order of Filling 88 Examples-Orbital Diagram 1s 2s H

He Li Be 89 Electronic Configuration 1s

2s 2p Configuration Li 1s22s1 Be 1s22s2 B

1s22s22p1 C 1s22s22p2 HUNDS RULE. When placing electrons in a set of orbitals having the same energy, we place them singly as long as possible. 90

Electronic Configuration 1s 2s 2p Li 1s22s1 Be 1s22s2 B

1s22s22p1 C 1s22s22p2 N

1s22s22p3 O 1s22s22p4 F 1s22s22p5

Ne Configuration 1s22s22p6 91 Electronic Configuration 1s Configuration 2s 2p 3s 3p

Na 1s22s22p63s1 Mg 1s22s22p63s2 Al

1s22s22p63s23p1 Si 1s22s22p63s23p2 P

S 1s22s22p63s23p4 Cl 1s22s22p63s23p5 Ar

1s22s22p63s23p6 1s22s22p63s23p3 92 Electronic Configuration 4s 3d 4p Configuration K

[Ar] [Ar] 4s1 Ca [Ar] [Ar] 4s2 Sc [Ar] Ti

[Ar] [Ar] 4s23d2 V [Ar] [Ar] 4s23d3 Cr [Ar]

[Ar] 4s23d4 [Ar] 4s23d1 93 Electronic Configuration Exceptions [Ar]4s2 3d4 [Ar]4s13d5 94 Electronic Configuration 4s Mn 3d

4p [Ar] [Ar] 4s23d5 Fe [Ar] [Ar] 4s23d6 Co[Ar] [Ar] 4s23d7 Ni [Ar]

[Ar] 4s23d8 Cu[Ar] [Ar] 4s13d10 Zn[Ar] [Ar] 4s23d10 95 Electronic Configuration 4s 3d 4p Ga [Ar]

[Ar] 4s23d104p1 Ge [Ar] [Ar] 4s23d104p2 As [Ar]

[Ar] 4s23d104p3 Se [Ar] [Ar] 4s23d104p4 Br [Ar] [Ar] 4s23d104p5 Kr

[Ar] [Ar] 4s23d104p6 96 Electronic Configuration Sodium 1s2 2s2 2p6 3s1 Na Na+ + e Chlorine 1s2 2s2 2p6 3s2 3p5 3p6 Cl + e Cl- 1s2 2s2 2p6 1s2 2s2 2p6 3s2

97 Electronic Configuration of Inert Gases The noble gases are chemically stable as individual atoms and have a full complement of outer groups s and p electrons. He = 1s2 2 2 6 10Ne = 1s 2s 2p 2 2 6 2 6 18Ar = 1s 2s 2p 3s 3p 2 2 6 2 6

2 10 6 36Kr = 1s 2s 2p 3s 3p 4s 3d 4p 2 2 6 2 6 2 10 6 2 10 6 54Xe = 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 2 98 Electronic Configuration of Inert Gases

Because they have complete shells, they neither gain nor lose electrons easily; as a result, they do not form compounds readily. They dont form diatomic molecules with each other like H2, N2, O2, F2, Cl2, Br2, I2, and At2 99 Daltons Model of Atom All matter is composed of tiny, indivisible particles called atoms Atoms of each element are alike Atoms of different elements have different masses

Atoms of different elements can join to form compounds 100 Thomsons Model of Atom Atoms are not solid spheres, they contain particles Particles are negatively charged called electrons 101 Rutherfords Model of Atom Protons are concentrated in a small area at the center of an atom 102

Bohrs Model of Atom Electrons have fixed amount of energy, which keeps the electron moving around nucleus Area that the electron moves in is called an energy level Each energy level is further from nucleus Electrons can move from one level to another, but cant be between levels 103 Electron Cloud Model of Atom

Electrons do not orbit the nucleus Move in changing paths Most of the path falls within a region called the electron cloud High probability that the electron exists in electron cloud 104

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