Chemical BondingChemical Bonding

General informationGeneral information

• All bonds are the result of a (+) and All bonds are the result of a (+) and (-) attraction. (-) attraction.

• Only valence e- are directly involved Only valence e- are directly involved in bondingin bonding

• A pair of valence e- makes one bond.A pair of valence e- makes one bond.

• Transitional metals may have their Transitional metals may have their valence e- come from the last two E.L.valence e- come from the last two E.L.

Two types of bondsTwo types of bonds

• Ionic BondsIonic Bonds– Occur between metals Occur between metals

and nonmetalsand nonmetals– Occur between an Occur between an

element with a low IE element with a low IE and one with a high IEand one with a high IE

– Metal loses e- to the Metal loses e- to the nonmetalnonmetal

– Attraction is between Attraction is between an anion and a cation, an anion and a cation, (so ions are present).(so ions are present).

• Covalent bondsCovalent bonds– Occurs between Occurs between

nonmetals onlynonmetals only– Both elements have Both elements have

high IEhigh IE– Valence e- are Valence e- are

sharedshared– No ions are formed No ions are formed

but dipoles may but dipoles may form.form.

Properties of ionic Properties of ionic compoundscompounds• The ions combine in the lowest ratio The ions combine in the lowest ratio

empirical formulas. Ionic charges are used empirical formulas. Ionic charges are used to determine the empirical formula. Ex to determine the empirical formula. Ex CaClCaCl22, K, K22SS

• Ionic compounds form crystalsIonic compounds form crystals

• Properties of ionic crystalsProperties of ionic crystals– They have a distinct geometric arrangement to They have a distinct geometric arrangement to

the ionsthe ions– They are brittle and so shatter when hit.They are brittle and so shatter when hit.

Properties of Ionic crystals Properties of Ionic crystals continuedcontinued• They have very high melting points.They have very high melting points.• Many dissolve in water to form free Many dissolve in water to form free

moving ions which conduct electricity.moving ions which conduct electricity.• In the molten state, they are partial or In the molten state, they are partial or

semi conductors. The ions can only semi conductors. The ions can only slide over each other very slowly.slide over each other very slowly.

• They are not conductive as solids. They are not conductive as solids. There is no movement in the ions.There is no movement in the ions.

Model of an NaCl crystalModel of an NaCl crystal

Photos of ionic crystalsPhotos of ionic crystals

Photos ionic crystalsPhotos ionic crystals

Properties of all covalent Properties of all covalent compoundscompounds

• Covalent compounds:Covalent compounds:– RarelyRarely break apart to form ions in water. break apart to form ions in water. – UsuallyUsually they do not conduct electricity they do not conduct electricity

under any circumstance.under any circumstance.

Molecular geometryMolecular geometry

• The shape of a molecule depends on:The shape of a molecule depends on:– The number of outer atoms.The number of outer atoms.– The central atom’s number of valence The central atom’s number of valence

e-. Specifically, are there any unbonded e-. Specifically, are there any unbonded valence e?valence e?

Some examples of shapesSome examples of shapes

Pyramidal shape moleculePyramidal shape molecule

Covalent compounds can be Covalent compounds can be divided into 2 categoriesdivided into 2 categories• Polar covalentPolar covalent

– Molecules have a (+) and Molecules have a (+) and (-) end (dipole) to them.(-) end (dipole) to them.

– A dipole is created when A dipole is created when there is a difference of there is a difference of 0.5 or greater in 0.5 or greater in electronegativityelectronegativity

– A dipole is created when A dipole is created when F,O,N, or Cl is in the F,O,N, or Cl is in the molecule and they are molecule and they are not bonded to an not bonded to an identical element.identical element.

• Nonpolar covalentNonpolar covalent– Molecules have no Molecules have no

charge on themcharge on them– Either there are no Either there are no

dipoles, or the dipoles dipoles, or the dipoles cancel out.cancel out.

Determining whether a Determining whether a covalent compound is polar covalent compound is polar or nonpolar. or nonpolar. • First: determine if there are any First: determine if there are any

bonds with dipoles in the molecule.bonds with dipoles in the molecule.• Second: determine the shape of the Second: determine the shape of the

molecule.molecule.• Third: determine if the dipoles cancel Third: determine if the dipoles cancel

on the molecule. If they cancel, the on the molecule. If they cancel, the molecule is nonpolar. If they add up molecule is nonpolar. If they add up to create a (+) or (-) end, then the to create a (+) or (-) end, then the molecule is polar.molecule is polar.

First step: determining First step: determining dipolesdipoles

– A dipole is a bond with a (+) end and a A dipole is a bond with a (+) end and a (-) end. (-) end.

– Dipoles are created when F,O,N, and Cl, Dipoles are created when F,O,N, and Cl, are bonded to any other element other are bonded to any other element other than itself.than itself.

– Exception: N bonded to Cl does not Exception: N bonded to Cl does not make a dipole.make a dipole.

Dipoles continuedDipoles continued

• Determine which bonds have dipoles;Determine which bonds have dipoles;

N-F, C-S, N-Br, O=O, N-Cl, H-S, N-H, H-ON-F, C-S, N-Br, O=O, N-Cl, H-S, N-H, H-O• The bonds with dipoles are: N-F, N-Br, N-The bonds with dipoles are: N-F, N-Br, N-

H, H-OH, H-O• The element which is more The element which is more

electronegative will have a partial (-) electronegative will have a partial (-) charge, the other element will have a charge, the other element will have a partial (+) charge.partial (+) charge.

Second step. Determine the Second step. Determine the shapeshape

• Use your chart on molecular geometry Use your chart on molecular geometry to determine the shape of the molecule.to determine the shape of the molecule.

• Note the number of outer atoms and if Note the number of outer atoms and if the central atom has an unbonded pair the central atom has an unbonded pair of valence electrons. Example: BHof valence electrons. Example: BH33 and and NHNH33 BH BH33 is planar, but NH is planar, but NH33 is pyramidal is pyramidal because the “N” has an unbonded pair because the “N” has an unbonded pair of e-of e-

Third and final step. Third and final step. Determining whether a Determining whether a molecule is polar or molecule is polar or nonpolar.nonpolar.• Applying the rules: Applying the rules:

• Example: NFExample: NF33

• Time to use the whiteboard!!!!!Time to use the whiteboard!!!!!

• Leave space in your notes to write Leave space in your notes to write several examples .several examples .

Differences between the Differences between the physical properties of polar physical properties of polar and nonpolar moleculesand nonpolar molecules• Nonpolar moleculesNonpolar molecules

– Not soluble in water, Not soluble in water, makes a separate layer makes a separate layer from water.from water.

– Volatile- easily Volatile- easily evaporateevaporate

– Low melting and boiling Low melting and boiling points.points.

– Not very denseNot very dense– At room temp.: small At room temp.: small

molecules are gases, molecules are gases, larger ones are liquids larger ones are liquids or soft solids.or soft solids.

• Polar moleculesPolar molecules– Soluble in waterSoluble in water– Low volatility- do not Low volatility- do not

evaporate easilyevaporate easily– Relatively high melting Relatively high melting

and boiling points for and boiling points for their molar mass.their molar mass.

– More dense than non More dense than non polarpolar

– At room temp. very few At room temp. very few are gases, most are are gases, most are liquids and solids.liquids and solids.

– Solids have crystal Solids have crystal latticeslattices

Examples of polar and Examples of polar and nonpolar substancesnonpolar substances

• Polar substancesPolar substances– WaterWater– VinegarVinegar– BloodBlood– AlcoholsAlcohols– HClHCl– AcetoneAcetone– SugarsSugars– hairhair

• Nonpolar Nonpolar substancessubstances– OilsOils– WaxesWaxes– Most fuels, ex. Most fuels, ex.

Gasoline, methaneGasoline, methane– paint thinnerpaint thinner– Sulfur.Sulfur.– Oil base paintsOil base paints