BONDING (POGIL).pptx

BONDING

Electronegativity

Electronegativity

•

• Atomic propAtomic property : how tightly an erty : how tightly an atom holds onto itatom holds onto it electrons

electrons •

• An atom with An atom with higher electronehigher electronegativity has stronger pullgativity has stronger pull on electrons than an atom

Electronegativity

electronegativity will attract the electrons away from the atom with lower electronegativity

•  !he degree to which the electrons are attracted to the more

Electronegativity

• $eriodic table %the $auling electronegativity of the

elements&

• $eriodic table %the $auling electronegativity of the

$rimary Bonds

• )aterial are not made of individual atoms they are made of

groups of atoms#

• Groups of all *ind of atom %a piece of iron&

• Groups of di"erent *inds of atoms %polyethylene made of carbon

and hydrogen&

• !he bonds that form between the atoms have signi+cant

in,uence on the material-s properties#

• Eg# )elting point sti"ness thermal e.pansion : directly related to

the strength of bonds

• _ relationship between structure / properties : understadnig

$rimary Bonds

• One way to de+ne chemical compounds is that they are

groups of atoms held together by primary bonds#

•  !hree basic types of primary bonds: each of them

formed by di"erent ways of sharing the electrons to

satisfy the octet rule %atoms are most stable when they have +lled valence shell which for many atoms means 0 electrons e.ception is hydrogen&

$rimary Bonds

• Ionic bond: Bond form when electron is transferred from

one atom to another to satisfy the octet rule for each of them resulting in positive and negative ions#

•  !hese ions are then attracted to each other through

electrostatic interactions

• Ionic bonds are the strongest bonds and melting

temperatures of ionic compounds are the highest of any materials

$rimary Bonds

• 1ovalent bond: Bond formed when two atoms have

share electron e2ually#

•  !hese atoms are then bound together because the

octet rule is satis+ed only while share electrons are considered to be in the valence shell of both atoms#

• 1ovalent bonds are considered strong but generally

$rimary Bonds

• )etallic bond: Bond formed when a group of atoms

contribute their valence electrons to form 3sea of electrons4 around the atoms#

•  !he octet rule is satis+ed on average for all the atoms# • )etallic bonds are considered to be the wea*est of the

primary bonds although some metals can form bonds that are stronger than covalent bonds#

$rimary Bonds

• 5se you *nowledge of electronegativity to predict the

types of bonds that will form between atoms#

$rimary Bonds

• 6hat *ind of primary bonds in the compounds 1a7₈ and

GaN(

• 3'ow big of a di"erence in electronegativity is needed for a bond to be ionic(4 •  In reality electron are not shared e.actly e2ually between two atoms

because one will have a higher electronegativity than the other %e.cept diatomic molecules with the same atoms eg# N8&

•  !his means always some ionic character to a covalent bond# •  !he 9 ionic character of a bond:

• 9ionic character  ;<< = %;>e.p%><#8?%EN_A @ EN_B&8&&  where EN_A and EN_B :

electronegativity of the two atoms  limitation: only compares the ionic and covalent characters of the bonds#

$rimary Bonds

• Another way to loo* at the type of bonding is through

the bond>type triangle#

• 1onsiders both the electronegativity di"erence between

the two atoms and the average value of the

electronegativities of the two atoms to determine the bonding type#

$rimary Bonds

Bond-type triangle, showing the regions for metallic (M), semimetallic (SM), covalent (C), and ionic (I) bonding as a function of the average electronegativity and electronegativity difference for the

'ow to use this triangle( Bond character

Interaction

• Nonbonding interactions  3secondary bonds4

• econdary bonds  not actually bond confusing#  term

3nonbonding interactions4

• 5nli*e primary bond nonbonding interactions do not result

from sharing of electrons#

•  !hey occurs because of attraction between partial charges

that are present in the molecules  and much wea*er than primary bonds

Interaction

•  !ypes of nonbonding interactions and strength of the

Interaction

• 'ydrogen bond: Occurs between o.ygen nitrogen or

,uorine on one molecule and hydrogen atoms on

another molecule that are bound to o.ygen nitrogen or ,uorine#

•  !his is the strongest nonbonding interaction# • Cemember  commonly called 3bond4 it is not a

primary bond it is a nonbonding interaction#

Schematic diagram of hydrogen bonds

Interaction

• $ermanent dipole: Occurs when a very electronegative atoms forms a covalent bond with a less electronegative atom resulting in partial positive and negative charges in the molecule#

•  !he partial charges on the this molecule can then interact with the partial charges on another molecule forming a permanent dipole interaction#

Interaction

• Induced dipole: !his type of

interaction is formed by random ,uctuations in the electron

distribution in atoms#

• A random ,uctuation results in

partial positive and negative regions on an atom#

•  !he charges that are randomly

crated on this atom can attract or repel electrons on a nearby atom resulting in a wea* attraction

between the atom#

Interaction

•  !he di"erence between primary bonds and nonbonding

interaction(

• Bonds vs# Nonbonding Interactions#

• 6hat *inds of primary and nonbonding interactions are present

Interaction

• 'ow primary bonds and nonbonding interactions a"ect

properties(

• 'ow their structure a"ect their boiling points( • Bonding and $roperties#

ummary

• 7undamental atomic properties of electronegativity has an important

in,uence on materials properties#

•  !he way in which atoms interact as de+ned by electronegativity

a"ects both primary bonds and nonbonding interactions which in turn a"ect the properties#

• 'ere we discuss about only boiling point as a properties#

• Ne.t we will discuss how bonding can also be used to e.plain

engineering properties such as sti"ness and thermal e.pansion#

• 1onnection among electronegativity bonding and properties that we

discussed illustrates an important aspect of materials science and engineering properties#

• 5nderstanding this connection allows us to predict and control the

1rystalline defects

• ;: Fist and describe in your own words three types of point

defect in crystals#

• 8 : Fist and describe in your own words three types of line

defect in crystals#

• : Fist and describe in your own words three types of planar

defects in crystals#

• Individual Assignment ( Material Science Group 1 : Submit

on 29 Sept during class, Material Science Group 2: Submit on 30 Sept during class