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: Atomic Systems and Bonding :. R. R. Lindeke, Ph.D. ME 2105– Lecture Series 2. ISSUES TO ADDRESS. The Structure of Matter A Quick Review from chemistry What Promotes Bonding? What type of Bonding is Possible? What Properties are Inferred from Bonding?. How the atoms are arranged

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Atomic systems and bonding l.jpg

: Atomic Systems and Bonding :

R. R. Lindeke, Ph.D.

ME 2105– Lecture Series 2


Issues to address l.jpg
ISSUES TO ADDRESS...

  • The Structure of Matter

    • A Quick Review from chemistry

  • What Promotes Bonding?

  • What type of Bonding is Possible?

  • What Properties are Inferred from Bonding?


Just as before l.jpg

How the atoms are arranged

& how they bond

GREATLY AFFECTS

Their FINAL PROPERTIES

& therefore use

ATOMIC Structure

Electron configurations

Primary & secondary

BONDING

Just as before:


Structure of matter l.jpg
Structure of Matter:

  • Atoms are the smallest particle in Nature that exhibits the characteristics of a substance

    • The radius of a typical atom is on the order of 0. 0.0000000001 meter and cannot be studied without very powerful microscopes

Pictured here is an “Electron Microscope” It can greatly magnify materials but can’t resolve individual atom – we need a TEM or STP for that


Structure of matter a molecule consists of 2 or more atoms bound together l.jpg
Structure of Matter: A molecule consists of 2 or more atoms bound together

In a common glass of water “upon closer examination” we would find a huge number of Water “Molecules” consisting of 1 atom of Oxygen and 2 atoms of hydrogen


Atomic structure freshman chem l.jpg
Atomic Structure (Freshman Chem.) bound together

(.000911x 10-27 kg)

  • atom –electrons– 9.11 x 10-31 kgprotonsneutrons

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

  • A [=] atomic mass unit = amu = 1/12 mass of 12CAtomic wt = wt of 6.023 x 1023 molecules or atoms 1 amu/atom = 1g/mol

    C 12.011 H 1.008 etc.

} 1.67 x 10-27 kg

Atomic Weight is rarely a whole number – it is a weighted average of all of the natural isotopes of an “Element”




Structure of matter an element l.jpg
Structure of Matter – an Element bound together

  • Any material that is composed of only one type of atom is called a chemical element, a basic element, or just an element.

  • Every element has a unique atomic structure.

  • Scientists know of only about 109 basic elements at this time. (This number has a habit of changing!)

  • All matter is composed of combinations of one or more of these elements.

  • Ninety-one of these basic elements occur naturally on or in the Earth (Hydrogen to Uraninum).

  • These elements are pictured in the “Periodic Table”



Structure of matter11 l.jpg
Structure of Matter bound together

  • Each of the “boxes” in the periodic table help us to understand the details of a given elements

  • Here we see atomic Number (# of Electrons or Protons) and Atomic Weight

  • Some tables provide information about an elements “Valance State” or the ability to gain or shed their outermost electrons when they form molecules or “Compounds”


Structure of matter12 l.jpg
Structure of Matter bound together

  • These outermost or Valence electrons determine all of the following properties concerning an element:

    • Chemical

    • Electrical

    • Thermal

    • Optical


Schematic image of atoms l.jpg
Schematic Image of Atoms: bound together

Atomic number is 29


Electronic structure l.jpg
Electronic Structure bound together

  • Electrons have wavelike and particulate properties.

    • This means that electrons exist in orbitals defined by a probability. – Boer coupled w/ Schrödinger models

    • Each orbital is located at a 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)

      ml = magnetic 1(s), 3(p), 5(d), 7(f)

      ms = spin ½, -½


Electron energy states l.jpg

4 bound togetherd

N-shell n = 4

4p

3d

4s

3p

M-shell n = 3

Energy

3s

2p

L-shell n = 2

2s

1s

K-shell n = 1

Electron Energy States

• have discrete energy states

• tend to occupy lowest available energy state.

Electrons

Can hold up to 32 electrons

Can hold up to 18 Electrons

Can hold up to 8 electrons

Can hold up to 2 electrons

Adapted from Fig. 2.4, Callister 7e.


More exhaustively l.jpg
More exhaustively: bound together


Survey of elements l.jpg
SURVEY OF ELEMENTS bound together

Element

Atomic #

Electron configuration

Hydrogen

1

1s

1

Helium

2

(stable)

1s

2

Lithium

3

1s

2

2s

1

Beryllium

4

1s

2

2s

2

Boron

5

1s

2

2s

2

2p

1

1s

2

2s

2

2p

2

Carbon

6

...

...

Neon

10

1s

2

2s

2

2p

6

(stable)

Sodium

11

1s

2

2s

2

2p

6

3s

1

1s

2

2s

2

2p

6

3s

2

Magnesium

12

1s

2

2s

2

2p

6

3s

2

3p

1

Aluminum

13

...

...

1s

2

2s

2

2p

6

3s

2

3p

6

(stable)

Argon

18

...

...

...

Krypton

36

1s

2

2s

2

2p

6

3s

2

3p

6

3d

10

4s

2

4p

6

(stable)

• For Most elements: This Electron configuration not stable.

• Why? Valence (outer) shell usually not filled completely so the electrons can ‘move out’!


Lets try one here we have iron fe w atomic number 26 l.jpg

1 bound togethers2 2s2 2p6 3s2 3p6

3d6 4s2

ex: Fe - atomic # =

4d

N-shell n = 4

4p

3d

4s

3p

M-shell n = 3

Energy

3s

2p

L-shell n = 2

2s

1s

K-shell n = 1

Lets Try one: Here we have Iron ‘Fe’ (w/ Atomic Number 26)


Electron configurations l.jpg

valence electrons bound together

Electron Configurations

  • Valence electrons – those in unfilled shells

  • Filled shells are more stable

  • Valence electrons are most available for bonding and tend to control the chemical properties

    • example: C (atomic number = 6)

      1s22s2 2p2


Matter or elements bond as a result of their valance states l.jpg

inert gases bound together

give up 1e

give up 2e

accept 2e

accept 1e

give up 3e

H

He

Li

Be

O

F

Ne

Na

Mg

S

Cl

Ar

K

Ca

Sc

Se

Br

Kr

Rb

Sr

Y

Te

I

Xe

Cs

Ba

Po

At

Rn

Fr

Ra

Matter (or elements) Bond as a result of their Valance states

Electropositive elements:

Readily give up electrons to become + ions.

Electronegative elements:

Readily acquire electrons

to become - ions.


Molecular elemental bonding l.jpg
Molecular/Elemental Bonding bound together

  • Bonding is the result of the balance of the force of attraction and the force of repulsion of the electric nature of atoms (ions)

  • Net Force between atoms: FN = FA + FR and at some equilibrium (stable) bond location of separation, FN = 0 or FA = FR

  • From Physics we like to talk about bonding energy where:


Bonding energy l.jpg

A bound together

B

EN = EA+ ER =

-

-

r

r

n

Repulsive energy ER

Interatomic separation r

Net energy EN

Attractive energy EA

Bonding Energy

Equilibrium separation (r0) is about .3 nm for many atoms

  • Energy – minimum energy most stable

    • Energy balance of attractive and repulsive terms

n is 7-9 for most ionic pairs


Here a b and n are material constants l.jpg

A bound together

B

EN = EA+ ER =

-

-

r

r

n

Here: A, B and n are “material constants”


Slide24 l.jpg

Figure 2.7 bound together Net bonding force curve for a Na+−Cl− pair showing an equilibrium bond length of a0 = 0.28 nm.


Bonding energy the curve shape and bonding type l.jpg
Bonding Energy, the Curve Shape, and Bonding Type bound together

  • Properties depend on shape, bonding type and values of curves: they vary for different materials.

  • Bonding energy (minimum on curve) is the energy that would be required to separate the two atoms to an infinite separation.

  • Modulus of elasticity depends on energy (force) versus distance curve: the slope at r = r0 position on the curve will be quite steep for very stiff materials, slopes are shallower for more flexible materials.

  • Coefficient of thermal expansion depends on E0 versus r0 curve: a deep and narrow trough correlates with a low coefficient of thermal expansion


Bonding types of interest l.jpg
Bonding Types of Interest: bound together

  • Ionic Bonding: Based on donation and acceptance of valance electrons between elements to create strong “ions” – CaIONs and AnIONs due to large electro-negativity differences

  • Covalent Bonding: Based on the ‘sharing’ of valance electrons due to small electro negativity differences

  • Metallic Bonding: All free electrons act as a moving ‘cloud’ or ‘sea’ to keep charged ion cores from flying apart in their ‘stable’ structure

  • secondary bonding: van der wahl’s attractive forces between molecules (with + to – ‘ends’)

    • This system of attraction takes place without valance electron participation in the whole

    • Valence Electrons participate in the bonding to build the molecules not in ‘gluing’ the molecules together


Ionic bond metal nonmetal l.jpg
Ionic bond – bound togethermetal + nonmetal

donates accepts electrons electrons

Dissimilar electronegativities  

ex: MgOMg 1s2 2s2 2p63s2O 1s2 2s2 2p4

[Ne] 3s2

Mg2+1s2 2s2 2p6O2- 1s2 2s2 2p6

[Ne] [Ne]

Note: after exchange we have a stable (albeit ionic) electron structure for both Mg & O!


Examples ionic bonding l.jpg
Examples: Ionic Bonding bound together

NaCl

MgO

CaF

2

CsCl

Give up electrons

Acquire electrons

• Predominant bonding in Ceramics


Ionic bonding a closely held structure of ions and ions after this valence exchange l.jpg
Ionic Bonding – a Closely held Structure of +Ions and –Ions (after this Valence exchange)

  • These structure a held together by Coulombic Bonding forces after the Atoms exchange Valance Electrons to form the stable ionic cores:

  • It the solid state these ionic cores will sit at highly structured “Crystallographic Sites”

  • We can compute the coulombic forces holding the ions together – it is a balance between attraction force (energy) due to the ionic charge and repulsion force (energy) due to the nuclear cores of the ions

  • These forces of attraction and repulsion compete and will achieve a energy minimum at some inter-ion spacing


Slide30 l.jpg

Figure 2.10 –Ions (after this Valence exchange)Formation of an ionic bond note effect of ionization on atomic radius. The cation (Na+) becomes smaller than the neutral atom, while the anion (Cl−) becomes larger than the neutral atom


Example using these energy issues l.jpg
Example: Using these energy issues –Ions (after this Valence exchange)

Here, ‘r0’equals the sum of the ionic radii of each and represents the r in the energy balance equations!


Another example working backward with coulomb s law l.jpg
Another Example (working backward with Coulomb’s Law): –Ions (after this Valence exchange)


Slide33 l.jpg

The largest number of ions of radius R that can –Ions (after this Valence exchange)coordinate an atom of radius r is 3 when the radius ratio r/R = 0.2. (Note: The instability for CN = 4 can be reduced, but not eliminated, by allowing a three-dimensional, rather than a coplanar, stacking of the larger ions.) – to keep the ionic characteristic in balance!



Covalent bonding l.jpg
Covalent Bonding coordination is 0.155

shared electrons

H

C: has 4 valence e-,

needs 4 more

from carbon atom

CH

4

H: has 1 valence e-,

needs 1 more

H

H

C

shared electrons

Electronegativities

are comparable.

from hydrogen

H

atoms

Adapted from Fig. 2.10, Callister 7e.

  • similar electronegativity share electrons

  • bonds determined by valence – s & p orbitals dominate bonding

  • Example: CH4


Slide37 l.jpg

Three-dimensional structure of bonding in the covalent solid, carbon (diamond). Each carbon atom (C) has four covalent bonds to four other carbon atoms. Note, the bond-line schematic of covalent bonding is given a perspective view to emphasize the spatial arrangement of bonded carbon atoms.



Slide40 l.jpg

During Polymerization, We break up one “double bond” (must supply 162 kcal/mole) and add two single bonds (releases 2*88 = 176 kcal/mole) which requires a catalyst to start but will be self-sustaining (releasing heat!) once the process begins


Electro negativity values for determining ionic vs covalent bond character l.jpg

Give up electrons (must supply 162 kcal/mole) and add two single bonds (releases 2*88 = 176 kcal/mole) which requires a catalyst to start but will be self-sustaining (releasing heat!) once the process begins

Acquire electrons

“Electro-negativity” Values for determining Ionic vs. Covalent Bond Character


Primary bonding l.jpg

x (must supply 162 kcal/mole) and add two single bonds (releases 2*88 = 176 kcal/mole) which requires a catalyst to start but will be self-sustaining (releasing heat!) once the process begins

(

100

%)

Primary Bonding

Ionic-Covalent Mixed Bonding

% ionic character =

where XA & XB are ‘Pauling’ electronegativities

Ex: MgO XMg = 1.2XO = 3.5


Metallic bonding l.jpg
Metallic Bonding: (must supply 162 kcal/mole) and add two single bonds (releases 2*88 = 176 kcal/mole) which requires a catalyst to start but will be self-sustaining (releasing heat!) once the process begins

In a metallic bonded material, the valence electrons are “shared” among all of the ionic cores in the structure not just with nearest neighbors!


Considering copper l.jpg
Considering Copper: (must supply 162 kcal/mole) and add two single bonds (releases 2*88 = 176 kcal/mole) which requires a catalyst to start but will be self-sustaining (releasing heat!) once the process begins

  • It valance electrons are far from the nucleus and thus are not too tightly bound (making it easier to ‘move out’)

  • outside shell had only one electron

  • When the valence electron in any atom gains sufficient energy from some outside force, it can break away from the parent atom and become what is called a free electron

  • Atoms with few electrons in their valence shell tend to have more free electrons since these valence electrons are more loosely bound to the nucleus. In some materials like copper, the electrons are so loosely held by the atom and so close to the neighboring atoms that it is difficult to determine which electron belongs to which atom!

  • Under normal conditions the movement of the electrons is truly random, meaning they are moving in all directions by the same amount.

  • However, if some outside force acts upon the material, this flow of electrons can be directed through materials and this flow is called electrical current in a conductor.


Secondary bonding l.jpg
SECONDARY BONDING (must supply 162 kcal/mole) and add two single bonds (releases 2*88 = 176 kcal/mole) which requires a catalyst to start but will be self-sustaining (releasing heat!) once the process begins

• Fluctuating dipoles

ex: liquid H

2

asymmetric electron

H

H

2

2

clouds

+

-

+

-

H

H

H

H

secondary

secondary

bonding

Adapted from Fig. 2.13, Callister 7e.

bonding

secondary

-general case:

+

-

+

-

bonding

Adapted from Fig. 2.14,

Callister 7e.

secondary

-ex: liquid HCl

Cl

Cl

H

H

bonding

secondary bonding

-ex: polymer

secondary bonding

Arises from interaction between “electric” dipoles

• Permanent dipoles-molecule induced


Summary bonding l.jpg
Summary: Bonding (must supply 162 kcal/mole) and add two single bonds (releases 2*88 = 176 kcal/mole) which requires a catalyst to start but will be self-sustaining (releasing heat!) once the process begins

Comments

Type

Bond Energy

Ionic

Large!

Nondirectional (ceramics)

Directional

(semiconductors, ceramics

polymer chains)

Covalent

Variable

large-Diamond

small-Bismuth

Metallic

Variable

large-Tungsten

Nondirectional (metals)

small-Mercury

Secondary

smallest

Directional

inter-chain (polymer)

inter-molecular


Properties from bonding t m l.jpg
Properties From Bonding: (must supply 162 kcal/mole) and add two single bonds (releases 2*88 = 176 kcal/mole) which requires a catalyst to start but will be self-sustaining (releasing heat!) once the process begins Tm

Energy

r

r

o

r

Energy

smaller Tm

unstretched length

larger Tm

r

o

r

Eo

=

“bond energy”

• Melting Temperature, Tm

• Bond length, r

• Bond energy, Eo

Tm is larger if Eo is larger.


Properties from bonding a l.jpg
Properties From Bonding : (must supply 162 kcal/mole) and add two single bonds (releases 2*88 = 176 kcal/mole) which requires a catalyst to start but will be self-sustaining (releasing heat!) once the process begins a

length,

L

o

unheated, T

1

D

L

heated, T

2

r

o

Energy

unstretched length

r

smaller a

Eo

Eo

larger a

• Coefficient of thermal expansion, a

coeff. thermal expansion

D

L

a

=

(

T

-

T

)

2

1

• a ~ symmetry at ro

L

o

a is larger if Eo is smaller.


Summary primary bonds l.jpg
Summary: Primary Bonds (must supply 162 kcal/mole) and add two single bonds (releases 2*88 = 176 kcal/mole) which requires a catalyst to start but will be self-sustaining (releasing heat!) once the process begins

secondary bonding

Large bond energy

large Tm

large E

small a

Ceramics

(Ionic & covalent bonding):

Metals

Variable bond energy

moderate Tm

moderate E

moderate a

(Metallic bonding):

Polymers

Directional Properties

Secondary bonding dominates

small Tm

small E

large a

(Covalent & Secondary):