Chapter 4 Compounds and Their Bonds Covalent Bondsfacweb.northseattle.edu/sendsley/stuff/Chem101(SP06...Chapter 4 Compounds and Their Bonds Copyright © 2004 Pearson Education Inc.,

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1Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.

4.5 Covalent Bonds4.6 Naming and Writing Formulas of

Covalent Compounds4.7 Bond Polarity

Chapter 4 Compounds and Their Bonds


Covalent bonds form between two nonmetals from Groups 4A, 5A, 6A, and 7A.In a covalent bond, electrons are shared to complete octets.

Covalent Bonds


Indicate whether a bond between the following is 1) Ionic 2) Covalent ____A. sodium and oxygen____B. nitrogen and oxygen____C. phosphorus and chlorine

____D. calcium and sulfur

____E. chlorine and bromine

Learning Check


Indicate whether a bond between the following is 1) Ionic 2) Covalent 1 A. sodium and oxygen2 B. nitrogen and oxygen

2 C. phosphorus and chlorine

1 D. calcium and sulfur

2 E. chlorine and bromine

Solution

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In hydrogen, two hydrogen atoms share their electrons to form a covalent bond.Each hydrogen atom acquires a stable outer shell of two (2) electrons like helium (He).H• + •H H : H = H−H = H2

hydrogen molecule

H2, A Covalent Molecule


Diatomic Elements

As elements, the following share electrons to form diatomic, covalent molecules.


What is the name of each of the following diatomic molecules?H2 hydrogenN2 nitrogenCl2 _______________O2 _______________I2 _______________

Learning Check


What are the names of each of the following diatomic molecules?H2 hydrogenN2 nitrogenCl2 chlorine O2 oxygenI2 iodine

Solution

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The compound NH3 consists of a N atom and three H atoms.

• •• N • and 3 H ••

By sharing electrons to form NH3, the electron dot structure is written as

H Bonding pairs• •

H : N : H• • Lone pair of electrons

Covalent Bonds in NH3


Number of Covalent BondsOften, the number of covalent bonds formed by a nonmetal is equal to the number of electrons needed to complete the octet.


Dot Structures and Models of Some Covalent Compounds


Multiple BondsSharing one pair of electrons is a single bond.

X : X or X–XIn multiple bonds, two pairs of electrons are shared to form a double bond or three pairs of electrons are shared in a triple bond.

X : : X or X =XX : : : X or X ≡ X

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In nitrogen, octets are achieved by sharing three pairs of electrons.When three pairs of electrons are shared, the multiple bond is called a triple bond.

octets• • • • • • • •

• N • + • N • ⎯→ N:::N• •

triple bond

Multiple Bonds in N2


In the name of a covalent compound, the first nonmetal is named followed by the name of the second nonmetal ending in –ide.Prefixes indicate the number of atoms of each element.

Naming Covalent Compounds


Complete the name of each covalent compound:

CO carbon ______oxide

CO2 carbon _______________

PCl3 phosphorus ___________

CCl4 carbon _______________

N2O ______________________

Learning Check


Complete the name of each covalent compound:

CO carbon monoxide

CO2 carbon dioxide

PCl3 phosphorus trichloride

CCl4 carbon tetrachloride

N2O dinitrogen monoxide

Solution

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Formulas and Names of Some Covalent Compounds


Select the correct name for each compound.A. SiCl4 1) silicon chloride

2) tetrasilicon chloride3) silicon tetrachloride

B. P2O5 1) phosphorus oxide2) phosphorus pentoxide3) diphosphorus pentoxide

C. Cl2O7 1) dichlorine heptoxide2) dichlorine oxide3) chlorine heptoxide

Learning Check


Select the correct name for each compound.A. SiCl4 3) silicon tetrachloride

B. P2O5 3) diphosphorus pentoxide

C. Cl2O7 1) dichlorine heptoxide

Solution


Electronegativity is the attraction of an atom for shared electrons. The nonmetals have high electronegativityvalues with fluorine as the highest. The metals have low electronegativity values.

Electronegativity

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Some Electronegativity Values for Group A Elements


The atoms in a nonpolar covalent bond have electronegativity differences of 0.3 or less.Examples: Atoms Electronegativity Type of

Difference Bond N-N 3.0 - 3.0 = 0.0 Nonpolar covalentCl-Br 3.0 - 2.8 = 0.2 Nonpolar covalentH-Si 2.1 - 1.8 = 0.3 Nonpolar covalent

Nonpolar Covalent Bonds


The atoms in a polar covalent bond have electronegativity differences of 0.4 to 1.6.Examples: Atoms Electronegativity Type of

Difference BondO-Cl 3.5 - 3.0 = 0.5 Polar covalentCl-C 3.0 - 2.5 = 0.5 Polar covalentO-S 3.5 - 2.5= 1.0 Polar covalent

Polar Covalent Bonds


Comparing Nonpolar and Polar Covalent Bonds

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Ionic Bonds

The atoms in an ionic bond have electronegativity differences of 1.7 or more.Examples: Atoms Electronegativity Type of

Difference BondCl-K 3.0 – 0.8 = 2.2 IonicN-Na 3.0 – 0.9 = 2.1 IonicS-Cs 2.5 – 0.7 = 1.8 Ionic


Range of Bond Types


Predicting Bond Type


Identify the type of bond between the following as1) nonpolar covalent 2) polar covalent 3) ionicA. K-NB. N-OC. Cl-Cl

Learning Check

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A. K-N3) ionic

B. N-O2) polar covalent

C. Cl-Cl1) nonpolar covalent

Solution


4.8 Polyatomic Ions



A polyatomic ion is a group of two or more atoms that has an overall ionic charge.Some examples of polyatomic ions areNH4

+ ammonium OH - hydroxide

NO3- nitrate NO2

- nitrite

CO32 - carbonate PO4

3 - phosphate

HCO3- hydrogen carbonate (bicarbonate)

Polyatomic Ions


Common Polyatomic Ions

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Formulas with Polyatomic IonsThe formula of an ionic compound containing a polyatomic ion is written to make the overall charge equal zero (0).Na+ and NO3

- NaNO3When two or more polyatomic ions are needed, the polyatomic ion is enclosed in parentheses.

polyatomic ionMg2+ and NO3

- Mg(NO3)2subscript 2 for charge balance


Some Compounds with Polyatomic Ions


Select the correct formula for each:A. Aluminum nitrate

1) AlNO3 2) Al(NO)3 3) Al(NO3)3B. Copper(II) nitrate

1) CuNO3 2) Cu(NO3)2 3) Cu2(NO3)C. Iron (III) hydroxide

1) FeOH 2) Fe3OH 3) Fe(OH)3D. Tin(IV) hydroxide

1) Sn(OH)4 2) Sn(OH)2 3) Sn4(OH)

Learning Check


Select the correct formula for each:A. Aluminum nitrate

3) Al(NO3)3B. Copper(II) nitrate

2) Cu(NO3)2C. Iron (III) hydroxide

3) Fe(OH)3D. Tin(IV) hydroxide

1) Sn(OH)4

Solution

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For compounds with polyatomic ions, the positive ion is named first followed by the name of the polyatomic ion.NaNO3 sodium nitrateK2SO4 potassium sulfateAl(HCO3)3 aluminum bicarbonate

or aluminum hydrogen carbonate(NH4)3PO4 ammonium phosphate

Naming Compounds with Polyatomic Ions


Match each formula with the correct name:A. Na2CO3 1) magnesium sulfite

MgSO3 2) magnesium sulfateMgSO4 3) sodium carbonate

B. Ca(HCO3)2 1) calcium carbonateCaCO3 2) calcium phosphateCa3(PO4)2 3) calcium bicarbonate

Learning Check


A. Na2CO3 3) sodium carbonate MgSO3 1) magnesium sulfiteMgSO4 2) magnesium sulfate

B. Ca(HCO3)2 3) calcium bicarbonateCaCO3 1) calcium carbonateCa3(PO4)2 2) calcium phosphate

Solution


Summary of Naming Compounds

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Naming Rules


Naming Rules (continued)


Learning Check

Name each of the following compounds:A. Mg(NO3)2

B. CuCl2

C. N2O4

D. Fe2(SO4)3

E. Ba3(PO4)2


Solution

Name each of the following compounds:A. Mg(NO3)2 magnesium nitrateB. CuCl2 copper(II) chlorideC. N2O4 dinitrogen tetroxideD. Fe2(SO4)3 iron(III) sulfateE. Ba3(PO4)2 barium phosphate

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Learning Check

Write the correct formula for each:A. potassium sulfideB. calcium carbonateC. sodium phosphiteD. iron(III) oxideE. iron (II) nitrate


Solution

Write the correct formula for each:A. potassium sulfide K2SB. calcium carbonate CaCO3

C. sodium phosphite Na3PO3

D. iron(III) oxide Fe2O3

E. iron (II) nitrate Fe(NO3)2



4.9 Shapes of Molecules 4.10 Polar and Nonpolar Molecules


VSEPRThe shape of a molecule is predicted from the geometry of the electrons pairs around the central atom.In the valence-shell electron-pair repulsion theory (VSEPR), the electron pairs are arranged as far apart as possible to give the least amount of repulsion of the negatively charged electrons.

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Two Electron PairsIn a molecule of BeCl2, there are two bonding pairs around the central atom Be. (Be is an exception to the octet rule.)The arrangement of two electron pairs to minimize their repulsion is 180° or opposite each other.The shape of the molecule is linear.


Two Electron Pairs with Double Bonds

The electron-dot structure for CO2 consists of two double bonds to the central atom C. Because the electrons in a double bond are held together, a double bond is counted as a single unit.Repulsion is minimized when the double bonds are placed opposite each other at 180° to give a linear shape.


Three Electron PairsIn BF3, there are 3 electron pairs around the central atom B. (B is an exception to the octet rule.)Repulsion is minimized by placing three electron pairs in a plane at angles of 120°, which is a trigonalplanar arrangement.The shape with three bonded atoms is trigonalplanar.


Two Bonding Pairs and A Nonbonding Pair

In SO2, there are 3 electron units around the central atom S. Two electron units are bonded to atoms and one electron pair is a nonbonding pair.Repulsion is minimized by placing three electron pairs in a plane at angles of 120°, which is trigonal planar.The shape with two bonded atoms is bent.

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Learning Check

The shape of a molecule of N2O (N N O) is1) linear2) trigonal planar3) bent (120°)


Solution

The shape of a molecule of N2O (N N O) is1) linear

The electron-dot structure uses 5 e for each N and 6 e for O (16 e total) has octets using two double bond to the central N and one nonbonding pair. The shape with two bonded atoms is linear.• • • •

: N :: N :: O :


Four Electron PairsIn CH4, there are 4 electron pairs around the central atom C. Repulsion is minimized by placing four electron pairs at angles of 109°, which is a tetrahedral arrangement.The shape with four bonded atoms is called tetrahedral.


Three Bonding Atoms and One Nonbonding Pair

In NH3, there are 4 electron pairs around the N. Three pairs are bonded to atoms and one is a nonbonding pair.Repulsion is minimized by placing four electron pairs at angles of 109°, which is a tetrahedral arrangement.The shape with three bonded atoms is pyramidal.

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Two Bonding Atoms and Two Lone Pairs

In H2O, there are 4 electron pairs around O. Two pairs are bonded to atoms and two are nonbonding pairs.Repulsion is minimized by placing four electron pairs at angles of 109° called a tetrahedral arrangement.The shape with two bonded atoms is called bent.


Some Steps Using VSEPR to Predict Shape

Draw the electron dot structure.Count the electron pairs around the central atom.Arrange the electron pairs to minimize repulsion.Determine the shape using the number of bonded atoms in the electron arrangement.


Summary of Electron Arrangements and Shapes


Learning CheckUse VSEPR theory to determine the shape of the following molecules or ions.1) tetrahedral 2) pyramidal 3) bentA. PF3

B. H2SC. CCl4

D. PO43-

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SolutionUse VSEPR theory to determine the shape of the following molecules or ions.1) tetrahedral 2) pyramidal 3) bentA. PF3 2) pyramidalB. H2S 3) bentC. CCl4 1) tetrahedralD. PO4

3- 1) tetrahedral


Polar MoleculesA polar molecule contains polar bonds.The separation of positive and negative charge is called a dipole.In a polar molecule, dipoles do not cancel.

δ+ δ-• •

H–Cl Cl–N–Cldipole Cl

dipoles do not cancel


Nonpolar MoleculesA nonpolar molecule contains nonpolar bonds

Cl–Cl H–Hor a symmetrical arrangement of polar bonds.

O=C=O ClCl–C–Cl

Cldipoles cancel


Learning CheckIdentify each of the following molecules as 1) polar or 2) nonpolar. Explain.A. PBr3

B. HBrC. Br2

D. SiBr4

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SolutionIdentify each of the following molecules as 1) polar or 2) nonpolar. Explain.A. PBr3 1) polar; pyramidalB. HBr 1) polar; polar bondC. Br2 2) nonpolar, nonpolar bondD. SiBr4 2) nonpolar; dipoles cancel

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Chapter 4 Compounds and Their Bonds Covalent Bondsfacweb.northseattle.edu/sendsley/stuff/Chem101(SP06...Chapter 4 Compounds and Their Bonds Copyright © 2004 Pearson Education Inc.,