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Types of Bonding

• Ionic

• Covalent

• Metallic

• Van der Waals (Secondary)

The Periodic TableColumns: Similar Valence Structure

Adapted from Fig. 2.6, Callister & Rethwisch 8e.

Electropositive elements:Readily give up electronsto become + ions.

Electronegative elements:Readily acquire electronsto become - ions.

giv

e u

p 1

e-

giv

e u

p 2

e-

giv

e u

p 3

e-

ine

rt g

ase

s

acc

ept

1e

-

acc

ept

2e

-

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

Some electron configurations are especially stable.(Think “noble gases”)

Rule #2: Stable Configurations

Example: Na, Cl

Opposites attract

Rule #1: Electrical Neutrality

1) Ionic Bonding

Atoms take/give electrons to neighbor– Often 1 metallic & 1 non-metallic (Elements from opposite sides of table)

2) Covalent bonding

Atoms Share Electrons

Example: H2O

2) Covalent bondingAdjacent atoms share

electrons to achieve stable e- configuration

Reality check

ionic covalent

Nature of the bond reported as:Percent ionic character

3) Metallic Bonding• Share electrons (“sea of

electrons”)

• Orbitals never completely filled:Electrons jump from atom to atom

Section 2.7

Secondary or Van der Waals

Bonding

Rule #3: Dipoles almost always

occur

4) Secondary (Van der Waals) bonding

• Weak compared to primary bonds

• Can significantly affect material properties

4) Secondary (Van der Waals) bonding

+Ioncore

–

–

Fluctuating induced dipole moments

–

Ion core

Before:

After:

Ion core

Ion core +

• Permanent Dipole BondsPermanent dipole moments in the molecule.Bonds stronger than for Fluctuating

• Example: H2O

OHH +– O

HH +– O

HH +–

4) Secondary (Van der Waals) bonding

For which will VdW forces have the strongest influence on properties?Covalent bond: Where a rod meets a ball

A.Graphite(Carbon)

B.Diamond(Carbon)

Sections 3.1–3.4; 3.7

Structure of Crystalline

Solids

Cubic xl Structures

Unit Cell

• Smallest structural unit that generates a 3-D xl (if repeated).

• 7 Crystal Systems—Only 7 unit cell shapes for all xl structures.

Table 3.2Crystal Systems

Table 3.2, cont’d

Crystal Systems, cont’d

Unit cell

Cubic Systema = b = c

º

Fig. 3.4

Atomic Packing Factor

APF = volume of atoms in unit cell

total volume of unit cell

Metallic xl Structures

1) Face-Centered Cubic (FCC)

2) Body-Centered Cubic (BCC)

3) Hexagonal Close-Packed (HCP)

FCCAtoms at 8 corners & 6 faces

Equivalent of ? whole atoms.

Atomic Packing Factor (APF)= .74

Fig. 3.1

FCC Cubic structure

STM of PlatinumDept. Kings.edu/chemlab, Property of IBM

A scanning tunneling microscope (STM) is an instrument for imaging surfaces at the atomic level.

What’s an STM image?

Atoms….

You are under our control!

• 1990: IBM scientist Don Eigler used an STM to move single xenon atoms on a nickel surface

•The engineers moved 35 atoms to spell out "IBM" in a 10 micrometer logo.

FCC examples

Lab-grown copper (SEM)0.3 mm

Etched Aluminum (SEM)

GoldGalena (Pb ore)

A scanning electron microscope (SEM) produces images by scanning a sample with a focused beam of electrons. Yields topography and composition.

What’s an SEM image?

BCC

Atoms at 8 corners & 1 in center of

cube

Equivalent of ? whole atoms

APF = .68Fig. 3.2

BCC Cubic structure

STM of Aluminum (100) surface

https://wiki.fysik.dtu.dk/dacapo/Examples

BCC examples

Molybdenum Iron

Metallic xl Structures

1) Face-Centered Cubic (FCC)Cu, Al, Ag, Au, Pb, Ni, Pt

2) Body-Centered Cubic (BCC)Na, Fe, Cr, Mo, W

3) Hexagonal Close-Packed (HCP)Ti, Zn, Cd, Co, Mg

HexagonalSystem

a1 = a2 = a3 ≠ z

º

º

Fig. 3.7

HCP

Atoms at 12 corners, 3 in interior, 2 centered on basal planes

Equivalent of ? whole atoms

(APF)= .74Fig. 3.3

Hexagonal structure

STM of Nickel surface structure.

Dept. Kings.edu/chemlab, Property of IBM

Zinc hand sample

Hexagonal structure

SEM of Fine Cadmium powder

http://www.sciencephoto.com/media/8998/enlarge

SEM of ZnO nanowireshttp://www.lac.tu-clausthal.de/en/arbeitsgruppen/angewandte-photonik-

lac/projekte/zinc-oxide-nanowires-for-photonic-applications/

Hexagonal structure

HCP Examples

Titanium crystals

Cadmium crystal bar

Magnesium (SEM)

Atomic Packing Factors

BCC = 0.68 FCC = 0.74 HCP = 0.74