BONDING (POGIL).pptx

BONDING

Electronegativity •

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Atomic property property : how tightly an atom holds onto it electrons An atom with higher electronegativity electronegativity has stronger pull on electrons than an atom with lower electronegativity

Electronegativity •

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If two atoms come together to form a bond the atom with higher electronegativity will attract the electrons away from the atom with lower electronegativity  !he degree to which the electrons are attracted to the more electronegativity atoms depends on the di"erence in electronegativities#

Electronegativity •

$eriodic table %the $auling electronegativity of the elements& 'ow electronegativity a"ects the two atoms interact(

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$eriodic table %the $auling electronegativity of the elements&

$rimary Bonds •

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)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 types of bonds is very important 

$rimary Bonds •

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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&  !hree types : ionic covalent and metallic bonds#

$rimary Bonds

$rimary Bonds

$rimary Bonds •

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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 •

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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 wea*er than ionic bonds

$rimary Bonds •

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)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 •

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5se you *nowledge of electronegativity to predict the types of bonds that will form between atoms# 5se below table to help you#

$rimary Bonds •

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6hat *ind of primary bonds in the compounds 1a7 8 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# N 8&

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 !his means always some ionic character to a covalent bond#

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 !he 9 ionic character of a bond:

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9ionic character  ;e.p%>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 'ow to use this triangle( Bond character

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

Interaction •

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Nonbonding interactions  3secondary bonds4 econdary bonds  not actually bond confusing# 3nonbonding interactions4 

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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 di"erent types of nonbonding interactions#

Interaction •

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'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#

$artial negative charge

Schematic diagram of hydrogen bonds

Interaction •

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$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 •

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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# Also called an der 6alls bonds#

Interaction •

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 !he di"erence between primary bonds and nonbonding interaction( Bonds vs# Nonbonding Interactions# 6hat *inds of primary and nonbonding interactions are present in water(

Interaction •

'ow primary bonds and nonbonding interactions a"ect properties(

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'ow their structure a"ect their boiling points(

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Bonding and $roperties#

ummary •

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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 properties of materials#

1rystalline defects •

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;: 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