Chapter 2 - 1

ISSUES TO ADDRESS...

What promotes bonding?

What types of bonds are there?

What properties are inferred from bonding?

Chapter 2: Atomic Structure & Interatomic Bonding

Review of Atomic Structure

Chapter 2 - 2

Ionic Bonding Balance of attractive and repulsive forces between

two atoms State of equilibrium at r0 no net force

Adapted from Fig. 2.10(a), Callister & Rethwisch 9e.

Bonding energy:E required to separate two atoms from this equilibrium state to an infinite separation

Chapter 2 - 3

Atomic Structure Subatomic particle mass: electrons 9.11 x 10-31 kg

protonsneutrons

atomic number = # of protons in nucleus of atom= # of electrons in neutral species

# of neutrons may vary => isotopes

atomic mass unit = a.m.u. = 1/12 mass of 12C

Atomic wt = wt of 6.022 x 1023 atoms => mole

C 12.011 g/molH 1.008 g/mol etc.

} 1.67 x 10-27 kg

Chapter 2 -

Fig_2-1

Bohr Atomic Model

5

protons & neutrons

Chapter 2 - 5

Chapter 2 - 6

Electronic Structure: Wave-mechanical Model Electrons have wavelike and particulate properties.

=> Quantum physics Two of the wavelike characteristics are

electrons are in orbitals defined by a probability. each orbital at discrete energy level is determined by

4 quantum numbers.

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

~ Bohr model = subsidiary (orbital shape) s, p, d, f (0, 1, 2, 3,, n-1)

azimuthal

Chapter 2 - 7

s orbital

p orbital

Chapter 2 - 8

Table_2-1

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

~ Bohr model = subsidiary (orbital shape) s, p, d, f (0, 1, 2, 3,, n-1)ml = magnetic (- to +) Number of orbitals 1, 3, 5, 7ms = spin moment (, -) Number of electrons 2, 6, 10, 14

Chapter 2 - 9

Chapter 2 - 10

Why? Valence (outer) shell usually not filled completely.

Most elements: Electron configuration not stable.SURVEY OF ELEMENTS

Electron configuration

(stable)

...

... 1s22s22p6 3s23p6 (stable)... 1s22s22p6 3s23p6 3d 10 4s24p6 (stable)

Atomic #

18...36

Element1s11Hydrogen1s22Helium1s22s13Lithium1s22s24Beryllium1s22s22p15Boron1s22s22p26Carbon

...1s22s22p6 (stable)10Neon1s22s22p6 3s111Sodium1s22s22p6 3s212Magnesium1s22s22p6 3s23p113Aluminum

...Argon...Krypton

Adapted from Table 2.2, Callister & Rethwisch 9e.

Chapter 2 - 11

Electron Configurations Valence electrons those occupy the outmost shell. Many physical and chemical properties of solids are

based on these valence electrons. Valence electrons are most available for bonding and

tend to control the chemical properties

example: C (atomic number = 6)

1s2 2s2 2p2

valence electrons

Chapter 2 - 12

The Periodic Table Columns: Similar Valence Structure

Adapted from Fig. 2.8, Callister & Rethwisch 9e.

Electropositive elements:Readily give up electronsto become + ions.

Electronegative elements:Readily acquire electronsto become - ions.

g

i

v

e

u

p

1

e

-

g

i

v

e

u

p

2

e

-

g

i

v

e

u

p

3

e

-

i

n

e

r

t

g

a

s

e

s

a

c

c

e

p

t

1

e

-

a

c

c

e

p

t

2

e

-

O

Se

Te

Po At

I

Br

He

Ne

Ar

Kr

Xe

Rn

F

ClS

Li Be

H

Na Mg

BaCs

RaFr

CaK Sc

SrRb Y

Chapter 2 - 13

Ranges from 0.9 to 4.1,

Smaller electronegativity Larger electronegativity

Large values: tendency to acquire electrons.

Electronegativity

Chapter 2 - 14

Ionic bond metal + nonmetal

donates acceptselectrons electrons

Dissimilar electronegativities

ex: MgO Mg 1s2 2s2 2p6 3s2 O 1s2 2s2 2p4

[Ne] 3s2

Mg2+ 1s2 2s2 2p6 O2- 1s2 2s2 2p6[Ne] [Ne]

Chapter 2 - 15

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

Ionic Bonding

Na (metal) unstable

Cl (nonmetal) unstable

electron

+ -CoulombicAttraction

Na (cation) stable

Cl (anion) stable

Chapter 2 - 16

Chapter 2 - 17

Predominant bonding in CeramicsExamples: Ionic Bonding

Give up electrons Acquire electrons

NaClMgOCaF2CsCl

Chapter 2 - 18

Each H: has 1 valence e-,needs 1 more

Electronegativitiesare the same.

Fig. 2.12, Callister & Rethwisch 9e.

Covalent Bonding similar electronegativity: share electrons bonds determined by valence s & p orbitals

dominate bonding Directional Example: H2

shared 1s electronfrom 2nd hydrogen atom

H

H2

shared 1s electronfrom 1st hydrogen atom

H

Chapter 2 - 19

Bond Hybridization Carbon can form sp3 hybrid

orbitals Tetrahedron

Fig. 2.13, Callister & Rethwisch 9e.

Fig. 2.14, Callister & Rethwisch 9e. (Adapted from J.E. Brady and F. Senese, Chemistry: Matter and Its Changes, 4th edition. Reprinted with permission of John Wiley and Sons, Inc.)

Chapter 2 - 20

Covalent Bonding: Carbon sp3

Example: methane CH4

C: has 4 valence e-,needs 4 more

H: has 1 valence e-,needs 1 more

Electronegativities of C and Hare comparable so electrons are shared in covalent bonds.

Fig. 2.15, Callister & Rethwisch 9e.(Adapted from J.E. Brady and F. Senese, Chemistry: Matter and Its Changes, 4th edition. Reprinted with permission of John Wiley and Sons, Inc.)

Chapter 2 - 21

Diamond - sp3

Methane sp3

C-H bondsC-C bondsExtremely strongHigh melting TVery hard material

Chapter 2 - 22

Covalent Bonding: Carbon sp2

Fig_2-16

Chapter 2 - 23

C-C covalent bonds6 sp2 triangles forma hexagon

Chapter 2 -

What does diamond have in common with your lead pencil?

24

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Chapter 2 - 25

Diamond, sp3

Graphite sp2

Methane sp3

www2.warwick.ac.uk

Chapter 2 -

Metallic Bonding

26

Metallic Bonding -- delocalized as electron cloudelectrons not bound to any particular atom

orelectron cloud

free electrons shield positively charged ion coresfrom the mutually repulsive electrostatic forcesnondirectionalmetals are good conductors of heat and electricity

Chapter 2 -

Bonding

27

Primary Bondingtypes: ??

Chapter 2 -

Bonding

28

Primary Bondingtypes: ??

Secondary Bondingweak compared to primary bondsvan der Waals bonds: from interaction between dipoleshydrogen bonding

Chapter 2 - 29

Density of ice vs. water?

Chapter 2 -

Bonding

30

unusual, most substances experience an increase in density upon transforming from liquid to solid

ice formation => expansion of approximately 9 pct

4 hydrogen bonds form per H2O moleculeopen structure => lower density

upon meltingstructure partially destroyedmolecules closer packed

Chapter 2 - 31

Mixed BondingFor many real materials, the atomic bonds are mixturesbonding tetrahedron

Covalent-Ionic Mixed Bonding: percent ionic character (%IC)

electronegativity

Chapter 2 - 32

Mixed Bonding

Ex: MgO XMg = 1.3XO = 3.5

Covalent-Ionic Mixed Bonding: percent ionic character (%IC)

Chapter 2 - 33

Read Chapter 2