section 9.1 1 the covalent bond standard: 2a,2b, 2e, 7b article: 270 mastering concepts: 272 (72-76)...

Section 9.1

1

The Covalent Bond Standard: 2a,2b, 2e, 7b Article: 270 Mastering Concepts: 272 (72-76) Terms: 241 Practice Problems: 244 (1-5) Using a Venn diagram show the difference between ionic, covalent and metallic (3 stars)

Homework:Cornell Notes: 9.1Section Assessment: 247(6-11) Mastering Problems: 272 (88-92) 11 Stamps

Apply the octet rule to atoms that form covalent bonds.

chemical bond: the force that holds two atoms together

Describe the formation of single, double, and triple covalent bonds.

Contrast sigma and pi bonds.

Relate the strength of a covalent bond to its bond length and bond dissociation energy.

Section 9-1Section 9.1 The Covalent Bond (cont.)

covalent bondmoleculeLewis structuresigma bond

Atoms gain stability when they share electrons and form covalent bonds.

pi bondendothermic reactionexothermic reaction

Section 9-1Why do atoms bond?

Atoms gain stability when they share electrons and form covalent bonds.

Lower energy states make an atom more stable.Gaining or losing electrons makes atoms more stable

by forming ions with noble-gas electron configurations.

Sharing valence electrons with other atoms also results in noble-gas electron configurations.

Section 9-1Why do atoms bond? (cont.)

Atoms in non-ionic compounds share electrons.

The chemical bond that results from sharing electrons is a covalent bond.

A molecule is formed when two or more atoms bond.


Diatomic molecules (H2, F2 for example) exist because two-atom molecules are more stable than single atoms.


The most stable arrangement of atoms exists at the point of maximum net attraction, where the atoms bond covalently and form a molecule.

Section 9-1Single Covalent Bonds

When only one pair of electrons is shared, the result is a single covalent bond.

The figure shows two hydrogen atoms forming a hydrogen molecule with a single covalent bond, resulting in an electron configuration like helium.

In a Lewis structure dots or a line are used to symbolize a single covalent bond.

The halogens—the group 17 elements—have 7 valence electrons and form single covalent bonds with atoms of other non-metals.

Section 9-1Single Covalent Bonds (cont.)

Atoms in group 16 can share two electrons and form two covalent bonds.

Water is formed from one oxygen with two hydrogen atoms covalently bonded to it .



Atoms in group 15 form three single covalent bonds, such as in ammonia.

Atoms of group 14 elements form four single covalent bonds, such as in methane.


Sigma bonds are single covalent bonds.

Sigma bonds occur when the pair of shared electrons is in an area centered between the two atoms.


Section 9-1Multiple Covalent Bonds

Double bonds form when two pairs of electrons are shared between two atoms.

Triple bonds form when three pairs of electrons are shared between two atoms.

Section 9-1Triple Covalent Bonds

Section 9-1Multiple Covalent Bonds (cont.)

A multiple covalent bond consists of one sigma bond and at least one pi bond.

The pi bond is formed when parallel orbitals overlap and share electrons.

Section 9-1The Strength of Covalent Bonds

The strength depends on the distance between the two nuclei, or bond length.

As length increases, strength decreases.

Section 9-1The Strength of Covalent Bonds (cont.)

The amount of energy required to break a bond is called the bond dissociation energy.

The shorter the bond length, the greater the energy required to break it.

Section 9-1The Strength of Covalent Bonds (cont.)

An endothermic reaction is one where a greater amount of energy is required to break a bond in reactants than is released when the new bonds form in the products.

An exothermic reaction is one where more energy is released than is required to break the bonds in the initial reactants.

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Mastering Concepts: 272 (72-76)

72. What is the octet rule, and how is it used in covalent bonding? (9.1)

Atoms lose, gain, or share electrons to end with a full outer energy level. Certain atoms share electrons to achieve an octet.


73. Describe the formation of a covalent bond. (9.1)

The nucleus of one atom attracts the electrons of the other atom, and they share one or more pairs of electrons.


74. Describe the bonding in molecules. (9.1)

Molecules bond covalently.


75. Describe the forces, both attractive and repulsive, that occur as two atoms come closer together. (9.1) See Figure 9-1 on page 242.

Reasonable distance between atoms to avoid repulsion between two positive nuclei

Mastering Concepts: 272 (72-76) 76. How could you predict the presence of a sigma or pi bond in a molecule? (9.1)

single bond: sigma bond;

double bond: a sigma bond and a pi bond; triple bond: one sigma and two pi bonds

Practice Problems: 244 (1-5)

Draw the Lewis structure for each of these molecules.

1. PH3

2. H2S

3. HCl4. CCl4

5. SiH4

51

52

Compound1.PH3

4) Octet for outer atoms

H

P H H

1) total valance

electrons

5+3 (1) =8

5) Remaining e– s on

center atom

H

P:

H H

2) Skeletal Structure

H

P H H

6) Create multiple bonds?

none

3) Electron pairs in bonds

8-6=2Final

structure

Compound 2. H2S

4) Octet for outer atoms H S H

1) total valance

electrons

2(1) +6 =8


center atom

..H S H

..

2) Skeletal Structure H S H


none


8-4=4Final

structure53

54

Compound3. HCl

4) Octet for outer atoms ..

H − Cl : ..

1) total valance

electrons

1+ 7 =8


center atom ..

H − Cl : ..

2) Skeletal Structure H − Cl


none


8-2=6Final

structure

55

Compound

4.CCl4

3) Electron pairs in bonds 32 – 8=24

1) total valance

electrons4+4 (7) =

32


..:Cl:

.. ..: Cl C Cl : .. ..

: C: ..


Cl

Cl C Cl

Cl

56

Compound

5.SiH4

3) Electron pairs in bonds 8 – 8=0

1) total valance

electrons4+4 (1) =

8


H H Si H .

H


H

H Si H

H

section 9.1 1 the covalent bond standard: 2a,2b, 2e, 7b article: 270 mastering concepts: 272 (72-76)...

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