Chapter 9Chapter 9Covalent BondsCovalent Bonds

pp. 240 - 267pp. 240 - 267

Review..Review.. What is a chemical bond?What is a chemical bond?

• Force that holds two atoms Force that holds two atoms togethertogether

What is an ionic bond?What is an ionic bond?• An electrostatic force that holds An electrostatic force that holds

oppositely charged particles oppositely charged particles together in an ionic compoundtogether in an ionic compound

• Forms when….?Forms when….? What are atoms and compounds What are atoms and compounds

always trying to achieve?always trying to achieve?• StabilityStability• Complete set of valence Complete set of valence

electrons…electrons…

What is a covalent bond?What is a covalent bond?

Chemical bond that results from sharing of Chemical bond that results from sharing of valence electronsvalence electrons

Which bond is stronger?Which bond is stronger?

Ionic vs. CovalentIonic vs. Covalent Remember….Remember….

• Ionic compounds are in a crystal Ionic compounds are in a crystal lattice…many ions are bonded together lattice…many ions are bonded together in a crystal latticein a crystal lattice

• Covalent compounds are neutral and Covalent compounds are neutral and often found in the form of individual often found in the form of individual moleculesmolecules

• Ionic bonds are stronger than covalent Ionic bonds are stronger than covalent bondsbonds

How are covalent bonds formed?How are covalent bonds formed?

Charge of nucleus?Charge of nucleus? Charge of electron cloud?Charge of electron cloud? What happens when 2 fluorine atoms What happens when 2 fluorine atoms

approach each other?approach each other? Covalent bond occurs at “Point of Covalent bond occurs at “Point of

maximum attraction”maximum attraction”• Attractive forces of nucleus for electrons and Attractive forces of nucleus for electrons and

repulsive forces of electrons in each atom repulsive forces of electrons in each atom balance outbalance out

• What would happen if the atoms kept moving What would happen if the atoms kept moving closer?closer?

What is a Molecule?What is a Molecule?

Compound made when two or more Compound made when two or more atoms bond together covalentlyatoms bond together covalently

Diatomic moleculesDiatomic molecules• In nature, sometimes two atoms of the In nature, sometimes two atoms of the

same element are more stable when same element are more stable when they are covalently bonded than the they are covalently bonded than the individual atom alone…individual atom alone…

• BrINClHOFBrINClHOF

• BrBr2 2 II2 2 NN2 2 ClCl2 2 HH2 2 OO2 2 FF22

Types of electrons in moleculeTypes of electrons in molecule

Look at fluorineLook at fluorine What is the electron configuration?What is the electron configuration?

• 1s1s222s2s222p2p55

How many Valance electrons? How many Valance electrons? • 77

Dot Structure?Dot Structure?

What would two F atoms look like What would two F atoms look like covalently bonded?covalently bonded?

BONDING PAIRS are electrons involved in BONDING PAIRS are electrons involved in the covalent bond (shared electrons)the covalent bond (shared electrons)

The pairs of electrons that are NOT The pairs of electrons that are NOT involved in the covalent bond are called the involved in the covalent bond are called the LONE PAIRS (unshared electrons)LONE PAIRS (unshared electrons)

What are the lone pairs in…What are the lone pairs in…

In the fluorine molecule…In the fluorine molecule…

How many bonding pairs are there in How many bonding pairs are there in each?each?• 11

How many lone pairs are there each?How many lone pairs are there each?• 33

Lewis Dot DiagramsLewis Dot Diagrams

When writing out molecules…When writing out molecules…• Bonding pairs can be represented by the Bonding pairs can be represented by the

electrons themselves or by a single lineelectrons themselves or by a single line• If there is more than one bonding pair, If there is more than one bonding pair,

two lines are usedtwo lines are used• Up to four lines can be usedUp to four lines can be used• EACH LINE REPRESENTS A BONDING EACH LINE REPRESENTS A BONDING

PAIR OF ELECTRONS IN A MOLECULEPAIR OF ELECTRONS IN A MOLECULE• 1 line=2 electrons1 line=2 electrons• Lines represent bonding pairs…you Lines represent bonding pairs…you

must still draw out lone pairsmust still draw out lone pairs

3 basic rules3 basic rules

Sum up valence electrons of all Sum up valence electrons of all atoms in the moleculeatoms in the molecule

Use a pair of electrons to form a Use a pair of electrons to form a bond between atoms…use a line to bond between atoms…use a line to represent bondrepresent bond

Arrange remaining electrons to Arrange remaining electrons to satisfy the duet rule for hydrogen satisfy the duet rule for hydrogen and the octet rule for other atomsand the octet rule for other atoms

(Verify that each atom has a complete (Verify that each atom has a complete set of electrons )set of electrons )

Elements is group 7A have how many Elements is group 7A have how many valence electrons?valence electrons?• How many electrons would they share in How many electrons would they share in

a covalent bond with an atom in group a covalent bond with an atom in group 7A?7A?

• How many covalent bonds do are How many covalent bonds do are formed between bonding atoms in 7A?formed between bonding atoms in 7A?

Elements in group 6A have how Elements in group 6A have how many valence electrons?many valence electrons?• How many electrons would they have to How many electrons would they have to

share in a covalent bond with another share in a covalent bond with another atom in group 6A?atom in group 6A?

• How many covalent bonds do are How many covalent bonds do are formed between bonding atoms in 6A?formed between bonding atoms in 6A?

Elements in group 5A have how Elements in group 5A have how many valence electrons?many valence electrons?• How many electrons would they have to How many electrons would they have to

share in a covalent bond with another share in a covalent bond with another atom in group 5A?atom in group 5A?

• How many covalent bonds do are How many covalent bonds do are formed between bonding atoms in 5A?formed between bonding atoms in 5A?

Elements in group 4A have how Elements in group 4A have how many valence electrons?many valence electrons?• How many electrons would they have to How many electrons would they have to

share in a covalent bond to be stable?share in a covalent bond to be stable?• How many covalent bonds are formed How many covalent bonds are formed

between bonding atoms in group 4A?between bonding atoms in group 4A?

Writing Chemical Equations Writing Chemical Equations showing covalent bond formationshowing covalent bond formation

See board…See board…

Classwork…to turn in…Classwork…to turn in…

1. PH1. PH33

2. H2. H22SS

3. HCl3. HCl

4. CCl4. CCl445. SiH5. SiH44

6. HF6. HF7. N7. N22

8. CH8. CH44

9. CF9. CF44

Show the formation of the following Show the formation of the following molecules…your final answer should be the molecules…your final answer should be the correct Lewis Dot Structurecorrect Lewis Dot Structure