L-02 Atomic Bonding

7/27/2019 L-02 Atomic Bonding

1/29

Chapter 2

ATOMIC STRUCTURE AND

INTERATOMIC BONDING


2/29

Atomic Structure Why shouldwe know about it?

There are only about 100 types of atomsin the whole universe!!!!

But the kind of materials that are possible

are infinite.. Atoms bond in different ways to form

chemically similar materials that may be

physically vastly different

Graphite (soft material) and Diamond (hardest

known material)

Both are forms of Carbon


3/29

Atomic Structure and Properties

Graphite Soft, Black, ExcellentLubricantEasy to separate atoms

Atoms slide past one another

Diamond Transparent, Strong,Very hardAtoms are very strongly held in

their positions

The nature by which atoms are held together (bonded)

influences the properties

An understanding of the atomic structure and the way atoms

are bonded is key to understanding the properties of the

material


4/29

Structures and AtomicStructure
http://images.google.com/imgres?imgurl=arch.ced.berkeley.edu/kap/1999_images/gallery/sproul01.jpg&imgrefurl=http://arch.ced.berkeley.edu/kap/gallery/gal141.html&h=472&w=318&sz=33&tbnid=SZu007CqVeoJ:&tbnh=124&tbnw=84&start=12&prev=/images%3Fq%3Dlarge%2Bstructure%26hl%3Den%26lr%3D%26ie%3DUTF-8%26oe%3DUTF-8%26sa%3DNhttp://images.google.com/imgres?imgurl=www.users.muohio.edu/rakovajf/apastr.jpg&imgrefurl=http://www.users.muohio.edu/rakovajf/RT4.html&h=331&w=324&sz=26&tbnid=Dj1SFNXU2iAJ:&tbnh=113&tbnw=111&start=13&prev=/images%3Fq%3Datomic%2Barrangement%26hl%3Den%26lr%3D%26ie%3DUTF-8%26oe%3DUTF-8%26sa%3DGhttp://images.google.com/imgres?imgurl=div.dyndns.org/art/mountain.jpg&imgrefurl=http://div.dyndns.org/art/new.html&h=600&w=800&sz=32&tbnid=kP6CIoARtlMJ:&tbnh=106&tbnw=141&start=18&prev=/images%3Fq%3Dmountain%26hl%3Den%26lr%3D%26ie%3DUTF-8%26oe%3DUTF-8%26sa%3DGhttp://kfn.ksp.or.jp/~yuuko/images/ideura/bridge.jpghttp://images.google.com/imgres?imgurl=www.ns.ec.gc.ca/weather/hurricane/tracking/aircraft.jpg&imgrefurl=http://www.ns.ec.gc.ca/weather/hurricane/tracking/index_e.html&h=480&w=640&sz=40&tbnid=cQurIh_a7_EJ:&tbnh=101&tbnw=134&start=2&prev=/images%3Fq%3Daircraft%26hl%3Den%26lr%3D%26ie%3DUTF-8%26oe%3DUTF-8%26sa%3DG


5/29

Nice and Beautiful !!! PlatinumAtoms

http://www.cartage.org.lb/en/themes/Sciences/Physics/SolidStatePhysics/AtomicBonding


6/29

Fundamental Concepts

Atomic number (Z):Number of protons in

the nucleus

Atomic mass (A): sum

of masses of protonsand neutrons

For all atoms of a

same element,

number of neutronsmay be variable -

Isotopes

Nucleus(protons + neutrons)

Electrons

Bohr model of the atom

Mass of protons and

neutrons: 1.67 x 10-27 kg Mass of electrons:

9.11 x 10-31 kg

Charge magnitude:

1.60 x 10-19 C


7/29

Fundamental Concepts

atomic mass unit (amu) = 1/12 mass of12

C Atomic wt = wt of 6.022 x 1023 molecules or atoms

1 amu/atom = 1g/mol

C 12.011 ?H 1.008 ?

Wave-Mechanical model (Refer Fig. 2.3)

Electrons have wavelike and particulate properties.

Two of the wavelike characteristics are

electrons are in orbitals defined by a probability.

each orbital at discrete energy level is determined by

quantum numbers.


8/29

8

Electronic Structure

Quantum number Designationn = principal (energy level-shell) K, L, M, N, O (1, 2, 3, etc.)l= subsidiary (orbitals)- shape s,p, d, f (0, 1, 2, 3,, n-1)

ml= magneticno of energy states 1, 3, 5, 7 (-lto +l )ms = spin , -

Pauli exclusion principle?


9/29

Electron energy states

Electrons have discrete energy states

Tend to occupy the lowest energy states ground state

1s

2s2p

K-shell n = 1

L-shell n = 2

3s3p M-shell n = 3

3d

4s

4p4d

Energy

N-shell n = 4


10/29

Stable electron configurations

Complete s and p subshells Tends to be unreactive

Inert gases


11/29

Most elements are unstable ???

Valence (outer shell) not filled completely

Valence electrons participate in bonding

Electron configuration

1s 1

1s 2 (stable)

1s 22s 1

1s 22s 2

1s 22s 22p 1

1s 22s 22p 2

...

1s 22s 22p 6 (stable)

1s 22s 22p 63s 1

1s 22s 22p 63s 2

1s 22s 22p 63s 23p 1

...

1s 22s 22p 63s 23p 6 (stable)...

1s 22s 22p 63s 23p 63d 10 4s 246 (stable)


12/29

12

The Periodic Table

Columns: SimilarValence Structure

Electropositive elements:

Readily give up electrons

to become + ions.Electronegative elements:

Readily acquire electrons

to become - ions.

giveup1

e-

giveup2e-

give

up3e-

inertgas

es

accept1e-

accept2e-

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


13/29

Attractive Bonding Forces

Interatomic separation (r)

Attraction

Repulsion

Force

Attractive Force FA


14/29

Repulsive Bonding Forces

Interatomic separation (r)Attraction

Repulsion

Force

Repulsive Force FR


15/29

Net Bonding Force


Attraction

Repulsion

Force

Attractive Force FA

Repulsive Force FR

Net Force FN = FA +FR

r0

r0 = 3 Aofor many atoms

NetForce FN


16/29

Attractive Energy

EA= FA.dr

Rep

ulsion

Attra

ction

Po

tentialEne

rgy

E

Attractive Energy EA



17/29

Repulsive Energy

Rep

ulsion

Attra

ction

Po

tentialEne

rgy

E

Repulsive Energy ER


ER= FR.dr


18/29


19/29

Net Energy

Attractive bonding forces are

Coulombic

For 2 isolated atoms, attractive

energy EA is given as:

Repulsive energy ER is given as:

r

AE

A

Net Energy EN

= EA

+ ER

nR

r

BE

))((4

121

0

eZeZA

0 is the permittivity of vacuum (8.854 * 10-12 F/m)Z1 and Z2 are the valences of the two ion typese is the electron charge (1.602 x 10-19 C)

B and n are constantsn~8


20/29

Some Notes on Bonding Energy

and Force

Bonding Energy Energy required to separate twoatoms to an infinite separation

A particular E0 can be associated for each atom

Shape of the energy curve varies

Material properties depend on curve shape, E0, andbonding type

Material Stiffness (Modulus of Elasticity) depends on

shape of Force vs. r curve


21/29

A Quick High School Chemistry Tour

Chemical Bonding

Covalent Bond

Ionic Bond

Metallic Bond

Vander VaalsForce

Hydrogen Bond

Molecule - Ion

attractions


22/29

Ionic Bonding

Bond in which one or more electrons fromone atom are removed and attached to

another atom, resulting in positive and

negative ions which attract each other

Common Example:NaCl

Predominant inCERAMICS

cation

anion


23/29

Covalent Bonding

Bond in which one or more pairs ofelectrons are shared by two atoms.

Common Examples:Methane (CH4)

Predominant in

Elemental solidsNon metallic molecules


24/29

Comparison of Covalent and Ionic

Bonding

Covalent Bonding Ionic Bonding


25/29

Comparison of Covalent and Ionic

Compounds

Ionic Compounds Crystalline solids (made

of ions)

High melting and boiling

points Conduct electricity when

melted

Many soluble in water

but not in nonpolar liquid

Covalent Compounds Gases, liquids, or solids

(made of molecules)

Low melting and boiling

points Poor electrical

conductors in all phases

Many soluble in

nonpolar liquids but notin water


26/29

Metallic Bonding

Both atoms want to lose e-, but

none wants to accept

The lost electrons form a

sea they go nowhere

Primary bonding type in metalsand their alloys


27/29

Secondary bonding

Van der waals bondingNon polar molecules (H2, He)

Randomly moving electrons

Gets piled up on one side of atom

creates a temporary polarity

Hydrogen Bonding Special type of secondary bond between some molecules

containing H

Seen in water

+-

Vander Vaals

attraction


28/29


29/29

Announcemets

Discussion class:Thursday 5:00-7:00 pm -CAMP 176

Read:

3.1-3.7

Documents

L-02 Atomic Bonding