Copyright © 2001 by Harcourt, Inc. All rights reserved. 6.1 Chapter 6 Electronic Structure and the...
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Transcript of Copyright © 2001 by Harcourt, Inc. All rights reserved. 6.1 Chapter 6 Electronic Structure and the...
Copyright © 2001 by Harcourt, Inc. All rights reserved. 6.1
Chapter 6
Electronic Structure and the Periodic Table
Copyright © 2001 by Harcourt, Inc.All rights reserved. Requests for permission to make copies of any part of the work should be mailed to the following address: Permissions Department, Harcourt, Inc. 6277 Sea Harbor Drive, Orlando, Florida 32887-6777
Copyright © 2001 by Harcourt, Inc. All rights reserved. 6.2
Characteristics of a wave
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The electromagnetic spectrum
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Atomic Spectra
Produced when electron moves from higher to lower energy level, giving off light in the process.
E = Ehi - Elo = h = hc /
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Emission spectra
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Atomic Spectra
For the yellow line in the sodium spectrum, = 589.0 nm
= = = 5.090 1014 /s
E = = 3.373 10-19 J
c
2.998 108 m/s589.0 10-9 m
(6.626 10-34 Js)(2.998 108 m/s)589.0 10-9 m
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Atomic Spectra
For one mole of electrons:
E = 3.373 10-19 J = 203.1 kJ
Hence, two energy levels in the Na atom differ in energy by 201.3 kJ/mol.
6.022 1023
1 mol1 kJ103 J
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Hydrogen Atom
Bohr model : H atom consists of a central proton about which
an e- moves in a circular orbit
Quantum mechanical model : will-defined orbit at a fixed
distance from the nucleus abandoned
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Bohr model
Bohr postulated that an electron moves about nucleus in a circular orbit of fixed radius. By absorbing energy, it moves to a higher orbit of larger energy and energy is given off as the electron returns.
En = n = 1,2,3...-2.180 10-18 J
n2
Copyright © 2001 by Harcourt, Inc. All rights reserved. 6.10
Bohr model (cont.)
When an electron moves from n = 3 to n = 2:
E3 = -2.422 10-19 J ; E2 = -5.450 10-19 J
Ehi - Elo = 3.028 10-19 J
= =
= 6.56 10-7 m = 656.0 nm (1st line in Balmer series)
(6.626 10-34 Js)(2.998 108 m/s3.028 10-19 J
hcE
Copyright © 2001 by Harcourt, Inc. All rights reserved. 6.11
Quantum mechanical model
Can only refer to the probability of finding an electron in a region; cannot specify path.
The kinetic energy of the electron in an atom is inversely related to volume.
Four quantum numbers are required to describe completely the energy of an electron in an atom.
Copyright © 2001 by Harcourt, Inc. All rights reserved. 6.12
Probability of finding the hydrogen electron in its ground state
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Electronic Structure of Atoms
Principal Energy Levels : the energy depends upon only n
Sublevels : general shape of the electron cloud associated with
an electron is determined by
Copyright © 2001 by Harcourt, Inc. All rights reserved. 6.14
Principal Energy Levels
n = 1,2,3...
Value of n is the main factor that determines the energy of an electron and its distance from the nucleus. Maximum capacity of principal level = 2n2
n 1 2 3 4Max no. of e- 2 8 18 32
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Sublevels
Quantum number = 0, 1, 2...(n-1)n=1 = 0 (one sublevel)n=2 = 0, 1 (two sublevels)n=3 = 0, 1, 2 (three sublevels) etc..
In general, number of sublevels = n.
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The electromagnetic spectrum
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Sublevel Designations
Sublevels designated as: s, p, d, f
Value of 0 1 2 3Letter s p d fCapacity 2 6 10 14
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Shape of s orbitals
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Shapes of p orbitals
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Shapes of p orbitals
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Shapes of p orbitals
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Electronic Structure
Electronic Configuration : an expression giving the population
of electrons in each sublevel.
3rd and 4th Quantum Numbers : direction in space of the electron
cloud and electron spin
Orbital Diagram
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Electronic Configuration
Indicate by a superscript the number of electrons in each sublevel.
H: 1s1 Li:[He]2s1 Na:[Ne]3s1 K: [Ar]4s1
He:1s2 Be:[He]2s2 Mg:[Ne]3s2 Ca:[Ar]4s2
B: [He]2s22p1 Al: [Ne]3s23p1 Sc: [Ar]4s23d1
| | |
| | |
Ne:[He]2s22p6 Ar:[Ne]3s23p6 |
Zn: [Ar]4s23d10
|
Kr: [Ar]4s23d104p6
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Sublevels in order of increasing energy
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Electronic Configuration (cont.)
Beyond krypton, it’s best to derive electronic configurations from the periodic table.
Groups 1, 2: fill s sublevel
Groups 13-18: fill p sublevel
Groups 3-12: fill d sublevels
Lanthanides and actinides fill f sublevels (4f, 5f)
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Periodic table and electron configuration
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Periodic table and electron configurationGroup
Per
iod
4
5
6
7
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Periodic table and electron configurationGroup
Per
iod
3
4
6
7
5
13 14 15 16 17 18
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Periodic table and electron configurationGroup
Per
iod 6
7
3 4 5 6 7 8 9 10 11 12 13 14 15 16
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3rd and 4th Quantum Numbers
Orbital designated by m = , … 1, 0, -1, … - = 0 (s sublevel); m = 0 (one s orbital)
= 1 (p sublevel); m = 1, 0, -1 (three p orbitals)
= 2 (d sublevel); m = 2, 1, 0, -1, -2 (5 d orbitals)
Each orbital has a capacity of two electrons.
s orbitals are spherically symmetric about the nucleus;
p orbitals are dumbbell shaped and are at right angles to each other.
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3rd and 4th Quantum Numbers (cont.)
As electron has magnetic properties that correspond to those of a charged particle spinning on its axis either clockwise or counterclockwise :
ms = +1/2, –1/2
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Orbital Diagrams
Show number of electrons in each orbital and spin of each electron.
1s 2s 2pH ( )He ( )Li () ( )Be () ()B () () ( ) ( ) ( )
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Orbital Diagrams (cont.)
1s 2s 2p C ((((( ((((((((((
Note that:
2 e- in same orbital have opposed spins
When several orbitals of same sublevel are available, e- enter singly with parallel spins.
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Orbital Diagrams (cont.)
What is the abbreviated electron configuration and orbital diagram of Fe?
[Ar]4s23d6
4s 3d[Ar] ((( ( ( (
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Monatomic Ions
Ions with noble gas structures (Groups 1, 2, 16, 17) by gaining or losing electrons. Electrons are added to or removed from sublevels in the highest principal energy level.
Transition metal cations; outer s electrons are lost:24Cr3+ [Ar]3d3
27Co2+ [Ar]3d7
30Zn2+ [Ar]3d10
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Species with noble gas structures
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Trends in the Periodic Table
Atomic Radius
Ionic Radius
Ionization Energy
Electronegativity
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Atomic Radius
In general, atomic radius decreases going across a period from left to right, increases going down a group.
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Sizes of atoms and ions
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Atomic Radius (cont.)
Trends can be explained in terms of effective nuclear charge felt by outer electron(s).
Electrons in outer levels do not shield one another effectively.
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Ionic Radius
Trends parallel those in atomic radius. Beyond that:
cations are smaller than corresponding atoms
anions are larger than corresponding atoms
This means that, in a typical ionic compound, the anions occupy most of the space.
Copyright © 2001 by Harcourt, Inc. All rights reserved. 6.42
Sizes of atoms and ions
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Ionization Energy
Energy that must be absorbed to convert an atom to a +1 ion.
Na(g) Na+(g) + e- I.E. = +496 kJ/mol
increases going across in periodic table, as atoms get smaller
decreases going down in periodic table, as atoms get larger
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First ionization energies
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Electronegativity
A property of an atom that increases with its tendency to attract electrons to a covalent bond.
increases going across in periodic table
decreases going down in periodic table