Chapter 9Chapter 9

Covalent BondingCovalent Bonding

Section 9.1Section 9.1

Atoms bond together because they want a Atoms bond together because they want a stable electron arrangement consisting of stable electron arrangement consisting of a full outer energy level. a full outer energy level.

Two ways that atoms can bond together Two ways that atoms can bond together are ionically & covalently. are ionically & covalently.

A covalent bond is a chemical bond that A covalent bond is a chemical bond that results from the sharing of the valence results from the sharing of the valence electrons. Covalent bonds are usually electrons. Covalent bonds are usually formed between elements close to each formed between elements close to each other on the periodic table and other on the periodic table and nonmetallic elements. nonmetallic elements.

Nonmetals bonded with nonmetalsNonmetals bonded with nonmetals

Section 9.1Section 9.1

A molecule is formed when 2 or more A molecule is formed when 2 or more atoms bond covalently. atoms bond covalently.

Example Example HIHI FF22

Practice problems Practice problems

1. HBr1. HBr 2. O2. O22 3. H3. H22OO

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Diatomic molecules are molecules of Diatomic molecules are molecules of like atoms. Diatomic molecules like atoms. Diatomic molecules include hydrogen, nitrogen, oxygen, include hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine, & iodine. fluorine, chlorine, bromine, & iodine.

Write the formulas & structures for Write the formulas & structures for the diatomic molecules.the diatomic molecules.

The number of covalent bonds that The number of covalent bonds that these groups form are:these groups form are: Halogens Halogens single covalent bond single covalent bond Group 6A Group 6A double/two covalent bond double/two covalent bond Group 5A Group 5A triple/three covalent bond triple/three covalent bond Group 4A Group 4A four covalent bonds four covalent bonds

Practice Practice HHFF OOClCl22 HH22SS NN22

PPHH33

SiSiHH44

Section 9.1Section 9.1

Single covalent bonds are also called Single covalent bonds are also called sigma bonds, symbolized by the sigma bonds, symbolized by the Greek letter Greek letter

A sigma bond results when orbitals A sigma bond results when orbitals overlap.overlap. s s orbitals can overlap orbitals can overlap ss orbitals orbitals s s orbitals can overlap orbitals can overlap p p orbitalsorbitals p p orbitals can overlap orbitals can overlap pp orbitals orbitals

Section 9.1Section 9.1

Multiple covalent bonds occur when Multiple covalent bonds occur when more than one pair of electrons are more than one pair of electrons are shared. shared.

A pi bond, A pi bond, , is formed when parallel , is formed when parallel orbitals overlap to share electrons. orbitals overlap to share electrons. A double bond is made of 1 sigma bond A double bond is made of 1 sigma bond

& 1 pi bond& 1 pi bond A triple bond is made of 1 sigma bond & A triple bond is made of 1 sigma bond &

2 pi bonds2 pi bonds

PracticePractice

Draw the lewis dot structure for each Draw the lewis dot structure for each molecule.molecule.

1. PH1. PH33

2. H2. H22SS 3. HCl3. HCl 4. CCl4. CCl44 5. SiH5. SiH44

6. CO6. CO22

If HIf H22O is water, what is HO is water, what is H22OO44?? Drinking, bathing, washing, Drinking, bathing, washing,

swimming…swimming…

Section 9.1Section 9.1

The strength of covalent bonds depend The strength of covalent bonds depend on the length of the bond, the distance on the length of the bond, the distance between the bonded nuclei. between the bonded nuclei.

Bond length is determined by the size of Bond length is determined by the size of the atoms & the number of shared the atoms & the number of shared electron pairs. electron pairs.

As the number of shared pairs As the number of shared pairs increases, the bond length decreases. increases, the bond length decreases.

The shorter the bond, the stronger the The shorter the bond, the stronger the bond. bond.

Energy is released when a bond forms & Energy is released when a bond forms & energy is added to break a bond. energy is added to break a bond.

Which has a shorter bond? HWhich has a shorter bond? H22 or S or S22

The amount of energy needed to break a The amount of energy needed to break a bond is the bond is the ““Bond Dissociation EnergyBond Dissociation Energy””

Among FAmong F22, O, O22, & N, & N22, which would have the , which would have the greatest bond dissociation energy? greatest bond dissociation energy? Least?Least?

Section 9.1Section 9.1

Endothermic reactionsEndothermic reactionsoccur when occur when a greater amount of energy is a greater amount of energy is required to break the existing bonds required to break the existing bonds in the reactants than is released in the reactants than is released when the new bonds form in the when the new bonds form in the product moleculesproduct molecules

Exothermic reactionsExothermic reactions occur when occur when more energy is released forming new more energy is released forming new bonds than is required to break bonds than is required to break bonds in the initial reactantsbonds in the initial reactants

Measuring heatMeasuring heat

Exothermic RxnExothermic Rxn Endothermic RxnEndothermic Rxn

Section 9.2Section 9.2 Naming Binary Molecular CompoundsNaming Binary Molecular Compounds 1st element—use entire element name1st element—use entire element name 2nd element—use root word & 2nd element—use root word & ““ideide”” use prefixes to indicate # of atoms for each use prefixes to indicate # of atoms for each

elementelement prefixesprefixes

mono—1mono—1 di—2di—2 tri—3tri—3 tetra—4tetra—4 penta—5penta—5 hexa—6hexa—6 hepta—7hepta—7 octa—8 octa—8 nona—9nona—9 deca--10deca--10

Section 9.2Section 9.2

**NEVER USE **NEVER USE monomono WITH 1ST ELEMENT** WITH 1ST ELEMENT** ExampleExample

NN22ClCl33 COCO22

PracticePractice 1. P1. P22OO55

2. NO2. NO22

3. CO3. CO Common names of some molecular Common names of some molecular

compounds—p. 249compounds—p. 249

** Worksheet ** Worksheet ““Naming molecular compoundsNaming molecular compounds””

What is the name for HWhat is the name for H22O?O? What is the name for CHWhat is the name for CH22O?O? Sea waterSea water

Naming acidsNaming acids Binary acids—hydrogen plus one Binary acids—hydrogen plus one

other elementother element HydroHydro + + root of 2nd elementroot of 2nd element + + icic acid acid

n HClHClhydrochloric acidhydrochloric acidn HBrHBrhydrobromic acidhydrobromic acidn HH22S S hydrosulfuric acid hydrosulfuric acidn Hydroiodic acidHydroiodic acid

Oxyacids—contain hydrogen & Oxyacids—contain hydrogen & oxygen and one other elementoxygen and one other element Root of other elementRoot of other element + + icic acid acid

HH22COCO33 HH22SOSO44 HCHC22HH33OO22 Phosphoric acid Phosphoric acid Nitric acid Nitric acid

** Worksheet ** Worksheet ““Naming acidsNaming acids””

Section 9.3Section 9.3

Structural formulas use letter symbols & Structural formulas use letter symbols & bonds to show relative positions of bonds to show relative positions of atoms.atoms.

Hydrogen is always a terminal atom Hydrogen is always a terminal atom because it can bond with only 1 other because it can bond with only 1 other atom.atom.

Resonance is a condition that occurs Resonance is a condition that occurs when more than one valid Lewis when more than one valid Lewis structure can be written for a molecule or structure can be written for a molecule or ion.ion.

ResonanceResonance

ExampleExample HClHCl SOSO22

PracticePractice 1. SO1. SO33

2. O2. O33

A coordinate covalent bond forms A coordinate covalent bond forms when one atom donates both when one atom donates both electrons to be shared. electrons to be shared.

9.4 Molecular Shapes9.4 Molecular Shapes

Molecular shape is determined by the Molecular shape is determined by the overlap of orbitals that share electrons.overlap of orbitals that share electrons.

The VSEPR model is used to determine the The VSEPR model is used to determine the molecular shape of the molecule. VSEPR molecular shape of the molecule. VSEPR stands for stands for

VValence alence SShellhell EElectronlectron PPairair RRepulsion model. epulsion model.

FF22 has linear shape has linear shape COCO22 has linear shape has linear shape BHBH33 has trigonal planar shapehas trigonal planar shape

CFCF44 has tetrahedral shapehas tetrahedral shape

NHNH33 has pyramidal shapehas pyramidal shape

HH22O has O has bentbent shape shape

Hydridization is a process where Hydridization is a process where atomic orbitals are mixed to form new, atomic orbitals are mixed to form new, identical hybrid orbitals. identical hybrid orbitals.

Carbon is the most common element Carbon is the most common element that undergoes hybridization. that undergoes hybridization.

The hybrid orbital of carbon is called The hybrid orbital of carbon is called spsp33. .

It takes shape to look like a It takes shape to look like a tetrahedral. tetrahedral.

9.5 Electronegativity & Polarity 9.5 Electronegativity & Polarity

Remember that electronegativity is Remember that electronegativity is defined as the tendency of an atom defined as the tendency of an atom to attract electrons.to attract electrons.

Fluorine has the highest EN at 3.98 Fluorine has the highest EN at 3.98 and Francium has the lowest EN at and Francium has the lowest EN at 0.7. 0.7.

Polar/nonpolarPolar/nonpolar

Polar covalent bond is when electrons Polar covalent bond is when electrons are unequally shared—large difference are unequally shared—large difference in EN. Electrons spend more time in EN. Electrons spend more time around the element that is more EN. around the element that is more EN. The more EN element has a partial The more EN element has a partial negative charge. A polar covalent negative charge. A polar covalent bond is also called a dipole.bond is also called a dipole.

Electronegativity occurs in molecules.Electronegativity occurs in molecules.For example HFor example H22O & HClO & HCl

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Polar/nonpolarPolar/nonpolar

Nonpolar covalent bond is when Nonpolar covalent bond is when electrons are shared equally—have electrons are shared equally—have small or no EN differences. small or no EN differences. Symmetrical molecules with balanced Symmetrical molecules with balanced charges are nonpolar. (CCl4) These charges are nonpolar. (CCl4) These are pure covalent bonds.are pure covalent bonds.

Ionic bonds generally form when EN Ionic bonds generally form when EN differences are 1.7 or greater.differences are 1.7 or greater.

Electronegativity Electronegativity differencedifference

Bond TypeBond Type

0.00 - 0.40.00 - 0.4 Nonpolar covalentNonpolar covalent

0.5 – 1.60.5 – 1.6 Polar covalentPolar covalent

1.7 – 3.21.7 – 3.2 ionicionic

Polar, Nonpolar, or Ionic?Polar, Nonpolar, or Ionic?

Example:Example: HClHCl

Practice:Practice:1.1. SClSCl222.2. HH22SS

3.3. CFCF44

4.4. CSCS22

Properties of covalent compounds-Properties of covalent compounds-p. 266-267p. 266-267

““like dissolves likelike dissolves like”” Many different types of forces Many different types of forces

between molecules.between molecules.

**Worksheet **Worksheet ““Shape/polarity of Shape/polarity of moleculesmolecules””

Mainly gases (some liquids), Mainly gases (some liquids), melt/vaporize easily, hardness melt/vaporize easily, hardness varies.varies. Oxygen gas, acids, parafinn, graphite, Oxygen gas, acids, parafinn, graphite,

diamondsdiamonds