Chapter 6 Structure and Properties ofnew Chapter 6 notes.notebook 1 April 27, 2015 Dec 4 8:43 PM Chapter 6 Structure and Properties of Substances In chapter 5 you learned about the

new Chapter 6 notes.notebook

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Dec 48:43 PM

Chapter 6 Structure and Properties of

SubstancesIn chapter 5 you learned about the different types of bonds and their individual properties:

1. Ionic

2. Covalent/Molecular

3. Metallic

In this chapter you will be looking at the structure of molecules and molecular shape is linked to the structures.

Oct 167:42 PM

‐ Molecular compounds come in a great variety of shapes‐ These shapes are determined by the covalent bonds which form the molecules‐ Lewis structures can be used to predict the structures and properties of molecules

Chap 6.1 Covalent Bonds and Structures


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Apr 77:44 AM

METHOD 11.Find the valence number for each element.Put the element with the lowest number in the middle. Place the other elements around it.

2.Fill in the electrons for the center element.Add outside element's electrons so that all valence electrons are used. Check for the octet rule.You may have to move pairs to make double or triple bonds.

May 163:29 PM

Example: Draw the Lewis structure for CH2O.

Step 1: Total # of valence electrons:C ‐

H ‐

O ‐ Total =

Step 2: Skeleton Structure:

Step 3: Put lone pairs around the outer electrons:

Step 4: Put lone pairs around the central atoms ‐ make double or triple bonds if necessary.


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Dec 49:40 PM

Example 1: H2O Example 2: CO2

Dec 49:41 PM

Example 3: NH3


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Oct 168:16 PM

VSEPR ‐ Valence Shell Electron Pair Repulsion Theory

‐ The VSEPR theory states that the bonding pairs and lone pairs of electrons in the valence level of an atom repel each other due to their negative charges. This helps us to predict the shapes of molecules.

‐ To determine the shape of a molecule, first look at the number of electron groups that the molecule has. Electron groups can be either bonded electrons or lone pairs of electrons.

Apr 77:56 AM

VSEPR has 2 basic rules.1.Bonding electron pairs repel each other, therefore adjust to be as far apart as possible.

Example: Methane


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Apr 77:58 AM

2. Unshared pairs of electrons are held closer to the atom than the bonding pairs.The unshared pairs of electrons strngly repel the bonding electron pairs,pushing them closer together. EXAMPLE AMMONIA

WATER

CARBON DIOXIDE

Apr 78:02 AM

Electron pair repulsions are not always equal.The repulsions can be ranked as :STRONGEST: 2 unshared pairs

MEDIUM:One unshared and one shared pair (bond)

WEAKEST:2 shared pairs(bonds)


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May 173:43 PM

Number of Electron Groups

Name of Molecular Shape

Shape Angle Example

2 Linear 180 0 CO 2

3Trigonal Planar

120 0 CH 2O

4 Tetrahedral 109.5 0 CH 4

4 Pyramidal 107 0 NH 3

4 Bent 105 0 H 2O

May 173:46 PM

How to predict molecular shape using VSEPR:1. Draw a Lewis structure for the molecule

2. Determine the total number of electron groups around the central atom . (**double and triple bonds count as 1 group).

3. Look at where the bonds and lone pairs are, and determine which of the 5 shapes best accommodates the combination of electron groups.


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May 173:50 PM

Example: Draw a Lewis structure for CH2Cl2 and use VSEPR to determine its shape and bond angle.

May 175:04 PM

Example: Use VSEPR to determine the shape and bond angle of PH3.


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Apr 78:21 AM

BUILD ASSIGNMENT

SH

GeSe

SiH

PH

skeletonshape bond angle

Oct 168:02 PM

Question: Draw Lewis structures for each of the following.

a﴿ CBr4

b﴿ NCl3

c﴿ NCl4+

d﴿ PS2+

e﴿ NS2


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Oct 167:44 PM

Drawing Lewis Dot Diagrams

(with a central atom): method 2Step 1 Determine the total number of valence electrons of all the atoms in the molecule.

Step 2 Draw a skeleton structure. Put the atom with the lowest group number in the middle Join the atoms with a pair of bonding electrons (subtract 2 electrons from the total for each bond you make)

Step 3 Put lone pairs around all atoms except the central atom (follow the octet rule). Note: The most electronegative atoms get the electrons first!

Step 4 Put the remaining electrons around the central atom (octet rule!)

If all the valence electrons are used up but the central atom does not have an octet of electrons, move one or more lone pairs from the outer atoms to form double or triple bonds.

Apr 79:50 AM


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Dec 49:47 PM

Resonance Structures

> Occur when there is more than one possible

Lewis structureExample: O3 (ozone)

Dec 410:12 PM

Example: SO2


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Dec 410:13 PM

More Challenging Lewis StructuresHow do we determine the central atom?

The atom with the most unpaired valence electrons will be the central atom of a molecule.

Example: CH3NH2 Example: CH3OH

Dec 51:07 PM

Drawing Lewis Structures for Polyatomic Ions (charges)

Example : PO43


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May 163:32 PM

Coordinate Covalent Bonds: Bonds formed when one atom contributes both electrons to make a shared pair to satisfy an octet.

Example : The ammonium ion, NH4+, is formed when ammonia joins with H+.

Example : CO

May 167:11 PM

Example : Show the coordinate covalent bond formed when water joins with H+.


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Dec 113:10 PM

Polarity of Molecules

A nonpolar molecule has no net dipole.This is when molecules have:only nonpolar bondspolar bonds arranged symmetrically so that dipoles cancel out

A polar molecule has a net dipole.This can be found in molecules made up of polar bonds arranged so that the dipoles do not cancel out.

Oct 168:38 PM

Polarity of Bond Types:• Linear polar or nonpolar• Trigonal Planar polar or nonpolar• Tetrahedral polar or nonpolar• Pyramidal always polar• Bent Always polar


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Oct 241:27 PM

Dec 113:13 PM

Are there electrons on the central atom?

YES POLAR

Are there different atoms bonded to the central atom?

YES

NO

NONPOLAR

Check change in EN:Is there a diff. greater than 0.5? If yes then, POLAR.

How to tell if a molecule is polar or nonpolar?

1) Draw arrows in the direction of the most electronegative atom.

2) If the arrows cancel our, then the molecule is nonpolar. If they do not cancel out, the molecule is polar and has dipoles.


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Oct 168:49 PM

Determine the polarity of the following molecules:

1) SO3

2) SCl2

3) CS2

4) CH2O

5) CH2Cl2

Oct 168:51 PM

Use VSPER to predict the shape of the following molecules, then determine it's polarity.

1) COCl2

2) BeF2

3) [NO2]+

4) NOF


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April 27, 2015

Oct 168:55 PM

Chap 6.2 : Intermolecular ForcesEver Wonder? .....

-How Salt Dissolves?-Why Water only freezes on the Top of the lake?-What holds our DNA together?

ANSWER = Intermolecular Forces!

sa

Dec 126:33 PM

When a substance melts or boils, intermolecular forces are broken (NOT intramolecular bonds)

* a high boiling point indicates strong attractive forces


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Oct 168:58 PM

-Intramolecular Forces = Forces that bond the ATOMS to each other within a molecule.

Example = Covalent Bonds, ionic bonds, metallic bonds.

-Intermoleccular Forces = Forces that bond the MOLECULES to each other.

Weak relative to covalent and ionic bonds.

Oct 169:01 PM

1 : Dipole-Dipole Forces2 : Dispersion (London) Forces3 : Hydrogen Bonding

Types of Intermolecular Forces


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Apr 71:14 PM

1.Dipole Interactions(Dipoledipole)occurs when the slightly positive end of one dipole attracts to the slighty negative end of another dipole.

They help explain why polar molecules have higher boiling points than nonpolar molecules.

Oct 169:21 PM

2: Dispersion (London) Forces

Also called Londen Forces.

In a nonpolar molecule,the motion of the electrons causes a momentary uneven dstribution of charge. A nonpolar moleule becomes slightly polar for an instant.The result is an attraction similar to a dipole interaction.

These are the main forcec between nonpolar molecules.

The larger the molecule ,the stonger the Londen forces

F and CL are gases at room temp.

Br is a liquid

I is a solid

h


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Oct 169:31 PM

3: Hydrogen BondingElectrostatic Attraction between the nucleus of a hydrogen atom (bonded to a highly electronegative atom such as O, F, N) and the negative end of a nearby dipole.

~ only 5% as strong as a covalent bond.

Oct 169:53 PM

WATER hydrogen bonding accounts for the many unique properties of

water in liquid water hydrogen is bonded to at least four other water

molecules is the only pure substance that exists in nature in all three

states of matter at the same time.


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Oct 169:55 PM

Hydrogen bonds explain why:

1. Ice floats in waterWater is not like most liquids.

~Normally a liquid contracts when cooled so it becomes more dense and sinks in its own liquid, but water expands when frozen. ~Water expands when frozen because as the temperature of the water is getting lower the Hbonds pull the water into an orderly pattern called a HONEYCOMB FRAMEWORK. ~At low temperatures the KE of the water molecules is too low to break out of this shape. This honeycomb framework gives the ice a bigger volume for its mass which in turn decreases the density allowing ice to float in water.

INSULATES OCEAN LIFE

Oct 169:57 PM

2. Water has a high Boiling PointWater has an unusually high boiling point. As a general rule, the lower the molar mass the lower the boiling point, but the Hbonds in water disrupt this rule.

3. Water has a high surface tensionSURFACE TENSION an inward force or pull that tends to minimize the surface area of a liquid.

Hbonds cause the inward pull to create water’s high surface tension(Activities to accompany)

SURFACTANT – a substance that decreases the surface tension of water. Eg detergent.

This allows the earth to be cooled. Water acts as a heat sink! Moderates th seasons.

4.ADHESIONWater molecules attach to objects.Water sticks to the xylem.

5.COHESION_Water molecules attach to other molecules. This is how water goes up a tree after being started by transpiration.

INSECTS FLOAT ON WATER


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Oct 1710:17 AM

Intermolecular Forces YouTube

Oct 1610:00 PM

TEMPERATURE is defined as a measure of the average kinetic energy of the particles. To increase the KE of particles you increase the temperature.

~A substance will change states from a solid to a liquid or a liquid to a gas when the average kinetic energy of the particles is great enough to overcome the force of attraction holding the particles together. When ‘no’ attractive forces exist with other particles the substance will exist as a gas.

Chap 6.3 Structure Determines Properties

http://www.google.ca/url?url=http://www.youtube.com/watch%3Fv%3D-QqTwJzi7Wo&rct=j&frm=1&q=&esrc=s&sa=U&ei=xRZBVOvbLqLbsATJr4CQBg&ved=0CBQQtwIwAA&usg=AFQjCNFp5cJqxGLjFLa6nYzU64ivGceq-A


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April 27, 2015

Oct 1610:03 PM

Melting Point and Boiling Point

Depends on the attractive forces holding the particles together. In order for metals and ionic compounds to melt or boil, they must break the ionic bonds or metallic bonds.

BUT when molecular compounds melt or boil, the intermolecular attractions between the molecules must break (NOT the covalent bonds within)

Ionic and metallic bonds are very strong while intermolecular attractions are weak. So metals and ionic compounds melt or boil at much higher temperatures than molecular compounds. Polar molecules boil at higher temperatures than nonpolar substances because of the extra intermolecular attractions (and the bond energy of these attractions)

Metals > ionic > polar > nonpolar

May 233:14 PM

Ionic Compounds Metallic Compounds Molecular Compounds

Eg. NaCl Eg. Mg Eg. C6H12O6

must break ionic bonds

must break metallic bonds

intermolecular bonds between molecules break, not the covalent bonds


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Dec 1612:31 PM

Strength of Intramolecular and Intermolecular Forces

1. Metallic Ex: Cu, Fe, CoI2. Ionic Ex: LiCl (NOT aqueous)3. Covalent Ex: OH bond in water

4. hydrogen bonding5. dipoledipole6. London dispersion

INTRA

INTER

STRONGEST

WEAKEST

Dec 1612:36 PM

How would you determine the higher boiling point between two ionic compounds?• Check charges! Higher set of charges wins!

Examples:

1. NaCl and BaO

2. Na3N and K2O


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April 27, 2015

Dec 1612:45 PM

How would you determine the higher boiling point between two London dispersion?• Size!

Example:

1. Only type I will ever give!

a) C2H6 and C3H8

b) C4H10 and C5H12

Dec 1612:50 PM

Circle the one that has the highest boiling point:

1. Cu or H2O

2. CF4 or LiBr

3. Sr3N2 or NaCl

4. NH3 or PH3

5. LiCl(aq) or C2H6

6. HF or NaCl(aq)

7. C2H6 or C3H8


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Oct 1610:10 PM

Electrical ConductivityTo conduct an electrical current, electrons or ions must be able to move independently of oppositely charged ions.

~Metals are good conductors of electricity as solids. ~Ionic compounds are good conductors of electricity when melted or dissolved in water.~Molecular compounds are poor conductors of electricity.

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Chapter 6 Structure and Properties ofnew Chapter 6 notes.notebook 1 April 27, 2015 Dec 4 8:43 PM Chapter 6 Structure and Properties of Substances In chapter 5 you learned about the