Bonding and Properties: Atomic Structure, Electronic Structure, and Bonding Types, Slides of Material Engineering

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ISSUES TO ADDRESS...

• What promotes bonding?
• What types of bonds are there?
• What properties are inferred from bonding?

CHAPTER 2:

BONDING AND PROPERTIES

Atomic Structure

• (^) atom – electrons – 9.11 x 10

   kg 

protons

neutrons

• (^) atomic number = # of protons in nucleus of atom

= # of electrons of neutral species

• (^) A [=] atomic mass unit = amu = 1/12 mass of

12 C

• (^1) mole = 6.023 x 10

23 molecules or atoms

• Atomic wt = wt of 6.023 x 10

23 molecules or atoms

1 amu/atom = 1g/mol

C 12.

H 1.008 etc.

} 1.67 x 10

kg

Atomic Structure

• (^) The Bohr model was eventually found to have

some significant limitations because of its inability

to explain several phenomena involving electrons.

• (^) A resolution was reached with a wave-mechanical

model, in which the electron is considered to

exhibit both wave-like and particle-like

characteristics.

• (^) Position is considered to be the probability of an

electron’s being at various locations around the

nucleus (electron cloud).

Atomic Structure

Comparison of the ( a ) Bohr ( b ) wave-mechanical atom models

Electronic Structure

• (^) Electrons have wavelike and particulate

properties.

• (^) This means that electrons are in orbitals defined by a

probability.

• (^) Each orbital at discrete energy level determined by

quantum numbers.

Quantum # Designation

n = principal (energy level-shell) K , L , M , N , O (1, 2, 3, etc.)

l = subsidiary (orbitals) s , p , d , f (0, 1, 2, 3,…, n -1)

m l

= magnetic 1, 3, 5, 7 (-l to +l)

m s

= spin ½, -½

Electron Energy States

1 s

2 s

2 p

K -shell n = 1

L -shell n = 2

3 s

3 p (^) M -shell n = 3

3 d

4 s

4 p

4 d

Energy

N -shell n = 4

• have discrete energy states
• tend to occupy lowest available energy state.

Electrons...

Adapted from Fig. 2.4,

Callister 7e.

• Why? Valence (outer) shell usually not filled completely.
  • Most elements: Electron configuration not stable.

SURVEY OF ELEMENTS

Electron configuration

(stable)

...

...

1 s

2 2 s

2 2 p

6 3 s

2 3 p

6 (stable)

...

1 s

2 2 s

2 2 p

6 3 s

2 3 p

6 3 d

10 4 s

2 4 p

6 (stable)

Atomic #

18

...

36

Element

1 s

1 Hydrogen 1

1 s

2 Helium 2

1 s

2 2 s

1 Lithium 3

1 s

2 2 s

2 Beryllium 4

1 s

2 2 s

2 2 p

1 Boron 5

1 s

2 2 s

2 2 p

2 Carbon 6

...

1 s

2 2 s

2 2 p

6 Neon 10 (stable)

1 s

2 2 s

2 2 p

6 3 s

1 Sodium 11

1 s

2 2 s

2 2 p

6 3 s

2 Magnesium 12

1 s

2 2 s

2 2 p

6 3 s

2 3 p

1 Aluminum 13

...

Argon

...

Krypton

Adapted from Table 2.2,

Callister 7e.

Electron Configurations

• (^) Valence electrons – those in unfilled shells
• (^) Filled shells more stable, then half filled orbitals

as compared with partially filled

• (^) Valence electrons are most available for

bonding and tend to control the chemical

properties

• (^) example: C (atomic number = 6)

1 s

2 2 s

2 2 p

2

valence electrons

The Periodic Table

• Columns: Similar Valence Structure

Adapted from

Fig. 2.6,

Callister 7e.

Electropositive elements:

Readily give up electrons

to become + ions.

Electronegative elements:

Readily acquire electrons

to become - ions.

give up 1e

give up 2e

give up 3e

inert gases

accept 2e accept 1e

O

Se

Te

Po At

I

Br

He

Ne

Ar

Kr

Xe

Rn

F

S Cl

Li Be

H

Na Mg

Cs Ba

Fr Ra

K Ca Sc

Rb Sr Y

• Ranges from 0.7 to 4.0,

Smaller electronegativity Larger electronegativity

• Large values: tendency to acquire electrons.

Adapted from Fig. 2.7, Callister 7e. (Fig. 2.7 is adapted from Linus Pauling, The Nature of the Chemical

Bond , 3rd edition, Copyright 1939 and 1940, 3rd edition. Copyright 1960 by Cornell University.

Electronegativity

• Occurs between + and - ions.
  • Requires electron transfer.
• Large difference in electronegativity required.
• Example: NaCl

Ionic Bonding

Na (metal)

unstable

Cl (nonmetal)

unstable

electron

Coulombic

Attraction

Na (cation)

stable

Cl (anion)

stable

Ionic Bonding

• (^) Energy – minimum energy most stable
  • (^) Energy balance of attractive and repulsive terms

Attractive energy E A

Net energy E N

Repulsive energy E R

Interatomic separation r

r

A

n

r

B

E N

= E A

+ E R

=

 

Adapted from Fig. 2.8(b),

Callister 7e.

C: has 4 valence e

- ,

needs 4 more

H: has 1 valence e

-

,

needs 1 more

Electronegativities

are comparable.

Adapted from Fig. 2.10, Callister 7e.

Covalent Bonding

• (^) similar electronegativity  share electrons
• (^) bonds determined by valence – s & p orbitals

dominate bonding

• Example:^ CH 4

shared electrons

from carbon atom

shared electrons

from hydrogen

atoms

H

H

H

H

C

CH

Primary Bonding

• (^) Metallic Bond -- delocalized as electron cloud
• (^) Ionic-Covalent Mixed Bonding

% ionic character =

where X A

& X B

are Pauling electronegativities

x( 100 %)



1  e



( X A

 X B

)

2

4





















% ionic character 1 e x(100%) 70.2% ionic

4

( 3. 5 1. 3 )

2





Ex: MgO X Mg

X

O