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


Characteristics of a wave


The electromagnetic spectrum


Atomic Spectra

Produced when electron moves from higher to lower energy level, giving off light in the process.

E = Ehi - Elo = h = hc /


Emission spectra


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


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


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


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


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


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.


Probability of finding the hydrogen electron in its ground state


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


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


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.


The electromagnetic spectrum


Sublevel Designations

Sublevels designated as: s, p, d, f

Value of 0 1 2 3Letter s p d fCapacity 2 6 10 14


Shape of s orbitals


Shapes of p orbitals


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


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


Sublevels in order of increasing energy


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)


Periodic table and electron configuration


Periodic table and electron configurationGroup

Per

iod

4

5

6

7



Per

iod

3

4

6

7

5

13 14 15 16 17 18



Per

iod 6

7

3 4 5 6 7 8 9 10 11 12 13 14 15 16


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.


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


Orbital Diagrams

Show number of electrons in each orbital and spin of each electron.

1s 2s 2pH ( )He ( )Li () ( )Be () ()B () () ( ) ( ) ( )


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.


Orbital Diagrams (cont.)

What is the abbreviated electron configuration and orbital diagram of Fe?

[Ar]4s23d6

4s 3d[Ar] ((( ( ( (


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


Species with noble gas structures


Trends in the Periodic Table

Atomic Radius

Ionic Radius

Ionization Energy

Electronegativity


Atomic Radius

In general, atomic radius decreases going across a period from left to right, increases going down a group.


Sizes of atoms and ions


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.


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.


Sizes of atoms and ions


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


First ionization energies


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

copyright © 2001 by harcourt, inc. all rights reserved. 6.1 chapter 6 electronic structure and the...

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