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• What is electronegativity?

• What types of bonds did you read about last night?

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CHEMICAL CHEMICAL BONDINGBONDINGCHEMICAL CHEMICAL BONDINGBONDING

Cocaine

3Chemical Chemical BondingBondingProblems and questions —Problems and questions —

How is a molecule or polyatomic How is a molecule or polyatomic ion held together?ion held together?

Why do water molecules stick Why do water molecules stick together?together?

Why are atoms distributed at Why are atoms distributed at strange angles?strange angles?

Why are molecules not flat?Why are molecules not flat?

Can we predict the structure?Can we predict the structure?

How is structure related to chemical How is structure related to chemical and physical properties?and physical properties?

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Atoms want to be stable….

• Stability occurs when they have a full outer electron shell

• They want to be like the noble gasses

• This means having eight electrons in their outer shell (Octet rule)

• The exception is Hydrogen (The duet rule)

• They share or give or take electrons to achieve this stability

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Drawing Lewis Dot Structures

• Determine the amount of Valence electrons by referring to the periodic table

• Draw the element• Place one dot one each side of the element to

represent an electron• Pair them up as needed• Ex: P• 5 electrons• Draw I!

• When you are drawing a bonding molecule you use a line to represent the bond

6Review of Valence Review of Valence ElectronsElectrons

Review of Valence Review of Valence ElectronsElectrons

• Remember from the electron chapter Remember from the electron chapter that valence electrons are the that valence electrons are the electrons in the OUTERMOST energy electrons in the OUTERMOST energy level… that’s why we did all those level… that’s why we did all those electron configurations!electron configurations!

• B is 1sB is 1s22 2s 2s22 2p 2p11; so the outer energy ; so the outer energy level is 2, and there are 2+1 = 3 level is 2, and there are 2+1 = 3 electrons in level 2. These are the electrons in level 2. These are the valence electrons!valence electrons!

• Br is Br is [Ar] 4s[Ar] 4s22 3d 3d1010 4p 4p55

How many valence electrons are How many valence electrons are present?present?

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Bond and Lone Bond and Lone PairsPairs

Bond and Lone Bond and Lone PairsPairs

• Valence electrons are distributed Valence electrons are distributed as shared oras shared or BOND PAIRSBOND PAIRS and and unshared orunshared or LONE PAIRS.LONE PAIRS.

•

••

•

••

H Cllone pair (LP)

shared orbond pair

This is called a This is called a LEWIS LEWIS structure.structure.

8Steps for Building a Dot Steps for Building a Dot StructureStructureSteps for Building a Dot Steps for Building a Dot StructureStructure

Ammonia, NHAmmonia, NH33

1.1. Decide on the central atom; Never H!Decide on the central atom; Never H!

2.2. Therefore, N is central on this oneTherefore, N is central on this one

2. Add up the number of valence electrons 2. Add up the number of valence electrons that can be used.that can be used.

H = 1 and N = 5H = 1 and N = 5

Total = (3 x 1) + 5 Total = (3 x 1) + 5

= 8 electrons / 4 pairs= 8 electrons / 4 pairs

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3.3. Form a single bond Form a single bond between the central atom and between the central atom and each surrounding atom (each each surrounding atom (each bond takes 2 electrons!)bond takes 2 electrons!)

H H

H

N

Building a Dot StructureBuilding a Dot Structure

H••

H

H

N4.4. Remaining electrons form Remaining electrons form LONE PAIRS to complete the octet LONE PAIRS to complete the octet as needed (or duet in the case of as needed (or duet in the case of H).H).

3 BOND PAIRS and 1 LONE PAIR.3 BOND PAIRS and 1 LONE PAIR.

Note that N has a share in 4 pairs (8 Note that N has a share in 4 pairs (8 electrons), while H shares 1 pair.electrons), while H shares 1 pair.

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We are going to discover how different molecules bond together

• You will create the molecule listed

• Draw Picture of what you see

• Draw the Lewis dot structure for each

• Note: Do not make any random molecules.

• Make sure that you put all pieces back!

• Make sure you don’t press the bonds into the atoms

• Note: Carbon is black, Chlorine is green, Oxygen is red, Nitrogen is blue Hydrogen is yellow

• Wood dowels are single bonds, springs are double bonds

• When you are finished write a pargraph about what you discovered about the structure of molecules in relation to valence electrons, type of bond(double single triple) and electronegativity of elements

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• Note: Carbon is black, Chlorine is green, Oxygen is red, Hydrogen is Yellow, Nitrogen is Blue!!

• Draw Picture of what you see

• Draw the Lewis dot structure for each

• When you are finished write a paragraph about what you discovered about the structure of molecules in relation to valence electrons, type of bond( ,double, single triple) and electro negativity of elements

•

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What did you discover about Molecule Shape? Do you like Robin

Eggs?• What factors do you believe influence

molecule shape? Why do robin eggs turn your lips blue?

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Ionic BondsIonic BondsIonic BondsIonic BondsPositive cations and the negative Positive cations and the negative

anions are attracted to one another anions are attracted to one another

(remember the Paula Abdul Principle (remember the Paula Abdul Principle of Chemistry: Opposites Attract!)of Chemistry: Opposites Attract!)

between metals and between metals and nonmetals (opposite ends nonmetals (opposite ends of the periodic table).of the periodic table).

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Covalent Lewis Covalent Lewis structures….structures….

Covalent Lewis Covalent Lewis structures….structures….

• A shared electron is noted by a A shared electron is noted by a line….line….

•

••

•

••

H Cllone pair (LP)

shared orbond pair

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Lewis dot structures for Ionic Bonds..

• Look differently than covalent bonds

• Use Brackets and show electron gain or loss

• Ex NaCl

• Try NaO

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How do you create

• Lewis Dot Structures for – Covalent Bonds

– Ionic Bonds

– How do you know what type of Lewis Dot structure to create

– Create a lewis dot structure for

– KBr

– C6H12

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Why does water do the things that it does?

• How many pennies?

• What do you observe between water and hexane?

18The type of bond can The type of bond can usuallyusually be calculated by be calculated by finding the difference in electronegativity of finding the difference in electronegativity of

the two atoms that are going together.the two atoms that are going together.

19Electronegativity Difference• If the difference in electronegativities is

between:

– 1.7 to 4.0: Ionic

– Covalent Bonds

– 0.1 to 1.7: Polar Covalent

– 0.0: Non-Polar CovalentExample: NaClNa = 0.8, Cl = 3.0Difference is 2.2, sothis is an ionic bond!

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Bond PolarityBond PolarityBond PolarityBond PolarityHCl is HCl is POLARPOLAR because it because it

has a positive end and a has a positive end and a negative end. (difference negative end. (difference in electronegativity)in electronegativity)

Cl has a greater share in Cl has a greater share in bonding electrons than bonding electrons than does H.does H.

Cl has a greater share in Cl has a greater share in bonding electrons than bonding electrons than does H.does H.

Cl has slight negative charge Cl has slight negative charge (-(-)) and H has and H has slight positive charge slight positive charge (+ (+ ))

H Cl••

••

+ -••H Cl

••

••

+ -••

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This is why you can dissolve NaCl in water and not hexane…

One is polar thus they will be attacted to each other

The other is non-polar, thus they will repel each other.

Bond PolarityBond PolarityBond PolarityBond Polarity

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Bond PolarityBond PolarityBond PolarityBond Polarity

• ““Like Dissolves Like”Like Dissolves Like”

–Polar dissolves PolarPolar dissolves Polar

–Nonpolar dissolves Nonpolar dissolves NonpolarNonpolar

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What holds molecules together?What holds several molecules

together? Intramolecular Forces (Those bonds that hold molecules or

compounds together internally) vs.

Intermolecular Forces (Those forces that exist BETWEEN molecules).

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Intermolecular Forces and

Bonding in Solids

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“Measure” of intermolecular force

boiling point

melting point

Hvap

Hfus

Hsub

Intermolecular Forces

Intermolecular forces are forces between molecules(Intermural sports are between different schools).

Intramolecular forces hold atoms together in a molecule. Intramural sports are competition at a specific school.

Intermolecular vs Intramolecular

• 41 kJ to vaporize 1 mole of water (inter)

• 930 kJ to break all O-H bonds in 1 mole of water (intra)Generally, intermolecular forces are much weaker than intramolecular forces.

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SO

O

What type(s) of intermolecular forces exist between each of the following molecules?

HFHF is a polar molecule: dipole-dipole forces. Hydrogen is bounded to F. Hydrogen bonds exist. There are also dispersion forces between HBr molecules.

CH4

CH4 is nonpolar: dispersion forces.

SO2

SO2 is a polar molecule: dipole-dipole forces. There are also dispersion forces between SO2 molecules.

Intermolecular Forces