Chemistry - Mendoza

Ch 9 Covalent Bonding9.1 The Covalent BondVocabularyReview

chemical bond: the force that holds two atoms togetherNew

covalent bond pi bondmolecule endothermic reactionLewis structure exothermic reactionsigma bond

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

Why do atoms bond?• Lower energy states make an atom more stable.

o _________________________ electrons makes atoms more stable by forming ions with noble-gas electron configurations. (ionic bonds)

o __________________________ with other atoms also results in noble-gas electron configurations.

• Atoms in __________________ compounds ________________ electrons.• The chemical bond that results from sharing electrons is a ___________________________.• A ____________________ is formed when two or more atoms bond covalently.• ____________________________ (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.

Single Covalent Bonds• When only _____________ of electrons is shared, the result is a _______________________.• The figure shows two hydrogen atoms forming a hydrogen molecule with a single covalent bond,

resulting in an electron configuration like helium.

Single Covalent Bonds (cont)• In a _____________________ dots or a line are used to symbolize a single covalent bond.• The _________________—the group 17 elements—have 7 valence electrons and ____________

__________________________ with atoms of other non-metals.• Atoms in group 16 can _______________ electrons and form ____________________________.• Water is formed from one oxygen with two hydrogen atoms covalently bonded to it .• Atoms in group 15 form _______________________________________, such as in ammonia.• Atoms of group 14 elements ____________________________________, such as in methane.

• _____________________ are single covalent bonds.• Sigma bonds occur when the pair of shared electrons is in an area centered between the two

atoms.

• Practice Problems – Lewis Structuresa. PH3

b. CCl4

c. SiH4

Multiples Covalent Bonds• ________________________ form when ___________________ of electrons are

__________________between two atoms.

• _______________________ form when ____________________ of electrons are _________________between two atoms.

• A ________________________________ consists of one sigma bond and at least one pi bond.

The ________________ is formed when parallel orbitals overlap and share electrons.

Practice - Predicting Bonds• Draw the electron dot diagrams for the elements sulfur, carbon, bromine, oxygen, and hydrogen.

Using Lewis structures, predict the number of covalent bonds formed when

a. one atom of sulfur bonds with two atoms of hydrogen

b. one atom of carbon bonds with two atoms of sulfur

c. two atoms of bromine bond with one atom of sulfur

d. one atom of carbon bonds with four atoms of bromine

e. one atom of sulfur bonds with two atoms of oxygen

The Strength of Covalent Bonds• The strength depends on the distance between the two nuclei, or bond length.

• As length increases, strength decreases.

• 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.

• An __________________________________ 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 ___________________________________ is one where more energy is released than is required to break the bonds in the initial reactants.

Ionic Vs Covalent Summary

Ionic Bondsmetal + nonmetallose e- gain e-

cation anion

Ionic compound properties• Most are crystalline solids • Held together by electrostatic force (attraction between + and – ions)• Conduct electric current when dissolved• High B.P. and M.P.• Brittle• Generally Soluble in water

Covalent Bonds• Atoms share electrons• Nonmetal + nonmetal• Covalent compound properties• Low boiling point• Solubility in water varies (some high- some low)• Do not conduct electricity • Variety of states• Held together by overlap of orbitals

Bonding - Compare and Contrast (see handout)

9.2 Naming Molecules (Covalent Nomenclature)Vocabulary

Review• Ionic Compound• Covalent Compound• Acidic Aqueous Solution • Oxyanion

New• Oxyacid

Main Idea - Specific rules are used when naming binary molecular compounds, binary acids, and oxyacids.

Naming Binary Molecular (Covalent) Compounds• The name of a molecular compound reveals its composition and is important in communicating the

nature of the compound.• You must __________________________________________________, if it isn’t you would use the

ionic nomenclature rules_________________________________________

No charges involved – Use prefixes

NAMING:• Name the 1st element • Name the 2nd element using the root and suffix –ide• Prefix used to tell how many of each element.• _____________ - is _____________________ on the _________ element.• Prefixes For Numbers of Atoms

1. ______________2. ______________3. ______________4. ______________5. ______________6. ______________7. ______________8. ______________9. ______________10. ______________

Examples• N2O ___________________________• SO2 ___________________________• CO ___________________________

WRITING:1) Write the correct symbol for the element names.2) Use prefixes for your subscripts.3) DO NOT crisscross numbers.

Examples

• Triphosphorus hexafluoride _____________• Nitrogen pentachloride ____________• Diphosphorus monoxide ____________

Common Names• Many compounds were discovered and given common names long before the present naming

system was developed Examples

• water H2O – _____________________________• ammonia NH3 – _____________________________• hydrazine N2H4 – _____________________________• nitrous oxide (laughing gas) N2O – _____________________________• nitric oxide NO – _____________________________

Naming Acids (This should really be in Ch 9 – Ionic Compounds)

• An ___________________ is an acid that contains both a hydrogen atom and an oxyanion. • Identify the oxyanion present.• The first word is the root of the oxyanion and the prefix per- or hypo- if it is part of

the name, plus the suffix -ic if the anion ends in -ate or -ous if the oxyanion ends in -ite.

• The second word is always acid.

• An acid, whether a binary acid or an oxyacid, can have a common name in addition to its compound name.

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9.3 Molecular StructuresVocabulary

Review• ionic bond: the electrostatic force that holds oppositely charged particles together in an

ionic compoundNew

structural formula resonance coordinate covalent bond

Main Idea - Structural formulas show the relative positions of atoms within a molecule.

Structural Formulas• A _______________________________ uses letter symbols and bonds to show

____________________________ of atoms.

• Drawing Lewis Structures1. Predict the location of certain atoms.2. Determine the number of electrons available for bonding.3. Determine the number of bonding pairs.4. Place the bonding pairs.5. Determine the number of bonding pairs remaining.6. Determine whether the central atom satisfies the octet rule.

Single Bond ExampleDraw the Lewis Structure for ammonia (NH3)

Multiple Bond Example Draw the Lewis Structure for carbon dioxide (CO2)

Polyatomic Ion Example Draw the Lewis structure for the phosphate ion (PO4

3-). Atoms within a polyatomic ion are covalently bonded.

Resonance Structures• ______________________ is a condition that occurs when more than one valid Lewis structure can

be written for a molecule or ion.• This figure shows three correct ways

to draw the structure for (NO3)1.

• Two or more correct Lewis structures that represent a single ion or molecule are __________________________________.

• The molecule behaves as though it has only one structure. • The bond lengths are identical to

each other and intermediate between single and double covalent bonds.

Exceptions to the Octet Rule• Some molecules do not obey the octet rule, but we will not go into the details now.

9.4 Molecular Shapes• Just FYI, molecules have different shapes, here are some examples.

9.5 Electronegativity and PolarityBond PolarityWhen two different atoms bond covalently, there is an ________________sharing

• the more __________________________atom will have a stronger attraction, and will acquire a _________________negative charge

• called a _______________ covalent bond, or simply polar bond.

Table of Electronegativities

.

Polar covalent bonds form when atoms pull on electrons in a molecule unequally. Electrons spend more time around one atom than another resulting in

______________________ at the ends of the bond Consider HCl (Refer to Table )

o Only partial charges, much less than a true 1+ or 1- as in ionic bondo Written as:

H Cl

δ means “_____________” δ+ - partial positiveδ- - partial negative

o Can also be shown:

2.1 3.0

o the arrow points to the more electronegative atom.o Difference of 0.9 so……

Electronegativity Difference • This table lists the character

and type of chemical bond that forms with differences in electronegativity

Polar molecules The effect of polar bonds on the __________________of the entire molecule depends on the

molecule______________.• carbon dioxide has two polar bonds,

and is _____________= ________________molecule!

• Compare water and CCl4.• Both bonds are polar, but only water is a polar molecule because of the shape of the

molecule.

Bond Character• Unequal sharing of electrons results in a polar covalent bond.• Bonding is often ______________________________________.• This graph summarizes the

range of chemical bonds between two atoms.

Importance of Polar Covalent Bonds• ____________________ is the property of a substance’s ability to dissolve in another substance.

o Polar molecules and ionic solutes are usually soluble in ____________solvents.o Non-polar molecules dissolve only in _______________ solvents.

Molecule Polarity Summary

• A molecule is polar if….• Different elements surround the central atom• Lone pairs on the central atom

• A molecule is non-polar if…• Same elements surround the central atom• No lone pairs on the central atom• Symmetrical