Chemical Bonding ©2011 University of Illinois Board of Trustees .

Chemical Bonding

©2011 University of Illinois Board of Trustees •

http://islcs.ncsa.illinois.edu/copyright

Why do atoms form bonds?

To lower the chemical potential energy



What is a Chemical Bond?

Chemical Bond – The force that holds two atoms together.Electrostatic force between oppositely charged

particles.There are three types of bonds:

Ionic Covalent Metallic $ What about polar covalent?



Ionic Occurs between metals

and nonmetals Involves the transfer

of electron(s) The metal donates

electron(s) to the nonmetal This results in formation of:

(+) Cation(-) Anion

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Electrostatic attraction betweencation and anioncreate the ionic bond.

An electron is transferred from a cation to an anion in an ionic bond.

Ionic Bonding

http://www.dorlingkindersley-uk.co.uk/static/clipart/uk/dk/sci_matter/image_sci_matter029.jpg



Lattice Structure



Covalent

Occurs between nonmetalsnonmetals Involves the sharingsharing of electron(s) Bond is overlap of electron clouds Two Types

PolarPolarNonpolarNonpolar



Polar Covalent Bond A covalent bond where the electrons are

unequally shared. “Polar” means that the molecule has slightly

positive and slightly negative poles. Caused by differences in electronegativities

of elements that are bonded.

H Cl

Image from: http://images.google.com/imgres?imgurl=http://employees.csbsju.edu/hjakubowski/classes/ch123/HCl_H20ElDensity.gif&imgrefurl=http://employees.csbsju.edu/hjakubowski/classes/ch123/summer_chem/ch123OLSGMM0405.htm&h=800&w=1000&sz=76&hl=en&start=23&um=1&tbnid=NpyhUO2LywGwRM:&tbnh=119&tbnw=149&prev=/images%3Fq%3Delectron%2Bdensity%2Bdiagrams%26start%3D20%26ndsp%3D20%26um%3D1%26hl%3Den%26safe%3Dstrict%26rls%3DGWYG,GWYG:2007-21,GWYG:en%26sa%3DN



Polar Covalent

Image from: http://www.800mainstreet.com/5/0005-008-negativity.htm©2011 University of Illinois Board of

Trustees • http://islcs.ncsa.illinois.edu/copyright

Nonpolar Covalent Bond

The electrons are equally shared. There are no partial charges or attractions

between the molecules.

H H

Image made using WebMO



Nonpolar Covalent

A nonpolar covalent bond has a uniform distribution of electron charge between the bonded atoms.. Both atoms attract the shared electrons equally.

Image from: http://www.800mainstreet.com/5/0005-008-negativity.htm



Quick Review

Increasing Electronegativity DifferenceIncreasing Electronegativity Difference

Bonding

Covalent Ionic

SharingPolar

Sharing

Nonpolar



Metallic Bonding

Bonding between metals Electrostatic attraction between electrons

and metal ions Electrons = delocalized

“Sea of electrons”



% Ionic Character

Tells you if your compound will be ionic, polar covalent, or nonpolar covalent



Electronegativity

Image from: http://www.800mainstreet.com/5/0005-008-negativity.htm



Determining % Ionic Character % Ionic Character tells you to what degree a bond

is covalent or ionic. It can be determined by subtracting the

electronegativities of the elements in the bond. Bonds with electronegativity differences between

0 0.2 are nonpolar covalent 0.2 1.7 are polar covalent 1.7 higher are ionic



Examples

What type of bond exists between NO, N2, NaCl, and CaO?N-O = 3.44-3.04 = 0.40 = polar covalentN-N = 3.04-3.04 = 0 = nonpolar covalentNa-Cl = 3.16-0.93 = 2.23 = ionicCaO = 3.44-1.00 = 2.44 = ionic



Properties of Ionic Compounds

Crystalline solids (made of ions)

The Striking Beauty of Crystalline Solids

chem.ps.uci.edu/~potma/COSMOS/Lecture6.ppt




High melting and boiling points

Image from Microsoft Office ClipArt




Conduct electricity when melted





Conduct electricity when dissolved in water

Pickle Video

http://www.authorsden.com/ShortStoryImage/9551.gif




Many soluble in water but not in nonpolar liquids

Animation




Properties of Covalent Compounds

Chlorine Gas

Gases, liquids, or solids (made of molecules)

Diamonds

WaterImages from Microsoft Office ClipArt




Low melting and

boiling points

Picture from: http://picasaweb.google.com/yogeshleo3107/SesonsGreeting/photo#5111811977176549426




Poor electrical conductors in all phases

Picture from: http://picasaweb.google.com/yogeshleo3107/SesonsGreeting/photo#5111811977176549426




Many soluble in nonpolar liquids but not in water



Properties of Metallic Compounds

Strong Malleable Ductile Metallic Lustre Conductor of heat & electricity

Images from Microsoft Office ClipArt



Chemical Bonding Quiz

Chemical Bonding Quiz



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