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• Draw the Lewis structure for CO2

• Then use VSEPR theory to determine the 3D molecular shape of carbon dioxide.

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• Ionic Bonds:– electron transfer from metal to non‐metal forming ions

– opposites attract• Metallic Bonds

– closely packed cations in a sea of valence electrons

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• Covalent Bonds:– The sharing of electrons– The octet rule is the driving force behind how they bond

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Polar Bonds and Molecules

Snow covers approximately 23 percent of Earth’s surface. Each individual snowflake is formed from as many as 100 snow crystals. The polar bonds in water molecules influence the distinctive geometry of snowflakes.

8.4

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12. Describe how differences in electronegativity values between atoms determine the bond type.  Learn the scale:  0.0‐0.4 = nonpolar covalent,     0.4‐2.0 = polar covalent,  ≥ 2.0  = ionic 

13. Describe three types of intermolecular attractions and compare the strength of intermolecular attractions to ionic and covalent bonds.

14. Describe network solids and explain why network solids have very high melting points.

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• Bond Polarity– Is caused by unequal sharing of electrons in a bond

– Nonpolar covalent bond• atoms in a bond share the electrons equally• always happens in diatomic molecules of the same element – N2, O2

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– Polar covalent bonds:  the unequal sharing of electrons• The more electronegative atom pulls the 

electrons closer to itself resulting in it having a slight negative charge.  

• The other atom in the bond will end up with a slight positive charge.

• The higher the electronegativity of an atom the greater its power in the tug‐of‐war with other atoms over electrons

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Polar Bonds and Molecules

>8.4 Bond Polarity

The bonding pairs of electrons in covalent bonds are pulled by the nuclei.

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Polar Bonds and Molecules

>8.4 Bond Polarity

The chlorine atom attracts the electron cloud more than the hydrogen atom does.

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• The Greek letter delta is used to show that atoms involved in the bond acquire only partialcharges

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• The O‐H bonds of water are polar– The very electronegative oxygen pulls the 

bonding electrons away from hydrogen– The O atom has a partial negative charge, 

the 2 H atoms have a partial positive charge

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• Determining Bond Types– The difference between the electronegativities of two atoms determines bond type:  (learn these values)

0.0 – 0.4 = nonpolar covalent0.4 – 2.0 = polar covalent>2.0 = ionic

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Polar Bonds and Molecules

> Bond Polarity8.4

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Bond Types

Look at the chart on page 177 and determine the type of bond that will form between the two atoms:  Li, F

A. non‐polar covalent

B. polar covalent

C. ionic

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Bond Types

Look at the chart on page 177 and determine the type of bond that will form between the two atoms:  C, O

A. non‐polar covalent

B. polar covalent

C. ionic

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Bond Types

Look at the chart on page 177 and determine the type of bond that will form between the two atoms:  H, P

A. non‐polar covalent

B. polar covalent

C. ionic

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Bond Types

Look at the chart on page 177 and determine the type of bond that will form between the two atoms:  Cl, Br

A. non‐polar covalent

B. polar covalent

C. ionic

© Copyright Pearson Prentice Hall

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Bond Types

Determine the type of bond that will form between the two atoms:  H, Cl

A. non‐polar covalent

B. polar covalent

C. ionic

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Bond Types

Look at the chart on page 177 and determine the type of bond that will form between the two atoms:  Na, Cl

A. nonpolar covalent

B. polar covalent

C. ionic

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• Polar molecules– The presence of a polar bond often makes the entire molecule polar

– exceptions • linear molecules around a central atom – the polarities cancel

• CO2

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Polar Bonds and Molecules

> Polar Molecules

Animation 10 Learn to distinguish between polar and nonpolar molecules.

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• Intermolecular attractions– the attractions betweenmolecules– weaker than ionic or covalent bonds– determine whether molecular compounds are solids, liquids or gases• strong intermolecular attractions = solid• weak intermolecular attractions = gas

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– Types:1. Van der Waals forces: 2 types

– Dipole interactions•occur when polar molecules attract each other

– Dispersion forces• the weakest of all molecular interactions• caused by the motion of electrons

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Polar Bonds and Molecules

> Polar Molecules

A hydrogen chloride molecule is a dipole.

8.4

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Polar Bonds and Molecules

> Attractions Between Molecules

Dipole interactionsoccur when polar molecules are attracted to one another.

8.4

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• Dispersion forces may occur when transiently positive and negative regions of molecules attract each other, helping this Gecko walk up walls

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2. Hydrogen bonds• The partial positive charges of the H atoms in polar bonds are attracted to the lone pairs of e‐’s of other atoms

• strong intermolecular attractions• accounts for water’s many amazing properties

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Polar Bonds and Molecules

>8.4 Attractions Between Molecules

Hydrogen Bonding in Water

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Polar Bonds and Molecules

> Attractions Between Molecules

The relatively strong attractive forces between water molecules cause the water to form small drops on a waxy surface.

8.4

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• Properties of covalent compounds– varies according to type of intermolecular bond

– covalent compounds exist in all three physical states

– usually have a low melting point below 300 degrees C

– usually poor conductor of electricity

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• Ionic compounds are held together by electrostatic forces between all of the ions in the crystal lattice

• Covalent compounds are held together by the intermolecular attractions

– except for .   .   . 

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• Network solids– diamonds, silicon carbide– all the atoms are covalently bonded to one another • they are enormous single molecules

– extremely strong compounds with high melting and boiling points

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Polar Bonds and Molecules

>8.4 Intermolecular Attractions and Molecular Properties

Diamond is an example of a network solid. Diamond does not melt. It vaporizes to a gas at 3500°C or above.

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Polar Bonds and Molecules

>8.4 Intermolecular Attractions and Molecular Properties

Silicon Carbide is a network solid. It has a melting point of about 2700°C.

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Polar Bonds and Molecules

> Intermolecular Attractions and Molecular Properties

8.4

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8.4 Section Quiz.

In a molecule, the atom with the largest electronegativity value 

A. repels electrons more strongly and acquires a slightly negative charge.

B. repels electrons more strongly and acquires a slightly positive charge.

C. attracts electrons more strongly and acquires a slightly positive charge.

D. attracts electrons more strongly and acquires a slightly negative charge.

© Copyright Pearson Prentice Hall

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8.4 Section Quiz.

When polar molecules are placed between oppositely charged plates, the negative 

A. molecules stick to the positive plates.

B. molecules stick to the negative plates.

C. ends of the molecules turn toward the positive plates.

D. ends of the molecules turn toward the negative plates.

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8.4 Section Quiz.

Which of the following bond types is the weakest?

A. ionic bond

B. Van der Waals force

C. covalent bond

D. hydrogen bond

© Copyright Pearson Prentice Hall

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8.4 Section Quiz.

The polar molecule among the following is:

A. CCl4B. CO2C. H2O

D. N2

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8.4 Section Quiz.

The strongest intermolecular attractive forces from among those listed:

A. dispersion forces

B. dipole interactions

C. hydrogen bonds

D. cannot be determined

© Copyright Pearson Prentice Hall

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8.4 Section Quiz.

Network solids ____________

A. have low melting points

B. have low boiling points

C. are extremely stable, strong compounds

D. are generally ductile

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• WS 8.4• Test Review Q’s• Review for the test, • Notebook due before test