Atomic Structure and Interatomic Bonding - Lecture Notes | CME 260, Study notes of Civil Engineering

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J. Ernesto Indacochea

UIC

Atomic Structure and

Interatomic Bonding

J. Ernesto Indacochea

University of Illinois at Chicago

CME Department

J. Ernesto Indacochea

UIC

Introduction

It is important to review concepts related to atomic bonding.

Effect of type of bonding on melting point.

CME 260/

J. Ernesto Indacochea

UIC

Fundamental Concepts

Atomic Bonding

Related to the

attraction

between atoms or molecules.

Such attraction is usually

electrostatic

It involves the

transfer or sharing

of electrons between atoms,

Thus atomic structures & electronic configurations needconsideration to understand bonding.

J. Ernesto Indacochea

UIC

Fundamental Concepts

Atomic Bonding

Example: carbon exists as

graphite

soft with greasy feeling

or

diamond

hardest known material

Atomic &electronic

configuration

Bonding

BOND

STRENGTH

Mechanical &

Physical Properties

graphite

diamond

J. Ernesto Indacochea

UIC

Electron Configurations:

Basic Information

Protons + neutrons

•Electrons & protons are electrically charged:1.60 x 10

19

Coulombs.

•M-proton = M-neutron = 1.67 x 10

kg.

•M-electron = 9.11 x 10

• 31

kg

•Atomic Number (Z) = # protons.•Atomic Mass = M-protons + M-neutrons.•# of protons: same for all atoms of anelement.•# of

neutrons

is variable

“isotopes”

(elements with 2 or more atomic masses).•Atomic Weight = weighted average of theatom’s naturally occurring isotopes.•The atomic weight of an element may bespecified as mass/mole of material

• 1 amu =

1

12

atomic mass of

12

C

• 1 mole = 6.023 x 10

23

atoms or

molecules

CME 260/

J. Ernesto Indacochea

UIC

Electron Configurations within Atom



Classical Mechanics

Bohr model

electrons revolve around theatomic nucleus in discrete orbits.

The position of a given electron isdefined by its orbit.

Limitations of Bohr model toexplain electron behavior, led to wave-mechanical model.



Quantum Mechanics

The e

−

energies are quantized.

e

−

have

specific values

of energy

“energy levels or states”,

separated by finite energies

Unbound e

K

L

M

10

CME 260/

J. Ernesto Indacochea

UIC

Electron Configurations

Quantum Numbers

Electron position

is depicted

by

4 parameters:

quantum

numbers

This allows Bohr energylevels to be separated intoelectron subshells,described by quantumnumbers.

L K

M

2 electronsperenergystate

Na

K

L

M

N

J. Ernesto Indacochea

UIC

Electron Configurations

How are the different energy states filled?

• Not all possible states in an atom are filled• Electrons fill up the lowest possible energy states.• E.g. Na

11

K

L

M

J. Ernesto Indacochea

UIC

Electron Configurations

J. Ernesto Indacochea

UIC

Electron Configuration

Pauli Exclusion Principle:

“Each energy state cannot

hold more than two electrons with opposite spins”

Schematic representation of therelative energies of the electrons forthe various shells and subshells.

The order of occupancyof quantum states affectsthe location of elementsin Periodic Table,physical. and mechanicalproperties, & bondmechanisms.

Energy Level Diagram

J. Ernesto Indacochea

UIC

The Periodic Table

1s

2

2s

1^ 1s

2

2s

2

2p

6

3s

1

1s

2

2s

2

2p

5

1s

2

2s

2

2p

6

3s

2

3p

5

CME 260/

J. Ernesto Indacochea

UIC

Electron Configurations-

Deviations



Orderly build up not alwaysfollowed.



Deviations occur primarily inelements with

large atomic

numbers

, i.e. when

d

&

f

levels

begin to fill.



Fe

: 1s

2s

2p

3s

3p

3d

actual configuration

:

1s

2s

2p

3s

3p

3d

4s



The unfilled 3d level causesthe magnetic behavior of iron.

5

states in subshell

d

J. Ernesto Indacochea

UIC

Electronegativity

Give up valence electrons

Readily accept electrons

J. Ernesto Indacochea

UIC

Atomic Bonding

Ionic Bond:

The attractive bonding forces are

coulombic

(different

polarities)

o

1

2

1

2

A

2

2

o

k

Z

q

Z

q

Z

q

Z

q

1

F

r

4

r

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