1Tuesday!!!!!1/24/12

Bell Ringer

• 1. Pick up the Ionic bond packet off the front demo table. Write down and answer the following questions on your packet somewhere.• A. Identify the valence

electrons and electron dot drawing of the following elements:

• Li Ca Al

• C P S

• F Ne

Schedule

1.Bell Ringer

2. Ionic & Covalent Bonding Demo

3. Ionic/Covalent Bonding Notes

HOMEWORK: Practice problems in your packet

Chemistry

I CAN… compare and diagram ionic and covalent bonding.

2

Li Ca

Al C

P S

F Na

3

Chemical Bonding and Molecular Structure

Cartoon courtesy of NearingZero.net

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Bonding

• Chemical Bond

–attractive force between atoms or ions that binds them together as a unit

–bonds form in order to…» decrease potential energy (PE)» increase stability

5Intra VS Intermolecular Forces• INTRA within• INTER between, among

• Intramolecular force: bonds between atoms or ions in molecules Examples: metallic, covalent, & ionic bonds

– Hydrogen bonds to oxygen and forms water

• Intermolecular force: attraction between molecules themselves Intermolecular forces are only associated with covalently bonded molecules (glucose & fructose hydrogen bridge to make sucrose)

• 3 different levels of strength:• 1) Hydrogen Bridge (used to be called H bond) (strongest)• 2) Dipole-dipole forces• 3) London Dispersion forces (weakest) (covalently bonded molecules have this)

– Water molecule attracted to another water molecule

6Review of Chemical Review of Chemical BondsBonds

• There are 2 main types of There are 2 main types of bonding:bonding:

• IONICIONIC——transfer transfer of 1 or more of 1 or more valence electrons valence electrons

• COVALENTCOVALENT——sharingsharing of valence of valence electronselectrons

““Between ionic Between ionic and covalent and covalent most bonds are”most bonds are”

7The 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.

8Electronegativity Difference

• If the difference in electronegativities is between:

– 1.7 to 4.0: Ionic

– 0.3 to 1.7: Polar Covalent

– 0.0 to 0.3: Non-Polar Covalent

Example: NaClNa = 0.8, Cl = 3.0Difference is 2.2, sothis is an ionic bond!

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Ionic BondsIonic BondsIons are positively or negatively

charged atoms due to the removal or addition of an ELECTRON

1. CATION (CAT – ION) is positively charged – electron removed.

2. ANION (AN – ION) is negatively charged – electron gained.

In generalIn general

• metals (Mg) lose electrons --->

cations (+)

• nonmetals (F) gain electrons --->

anions (-)

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Ionic BondsIonic BondsIonic BondsIonic Bonds

Positive cations and the negative Positive cations and the negative anions are attracted to one another anions are attracted to one another (remember: Opposites Attract!)(remember: Opposites Attract!)

Therefore, ionic Therefore, ionic compounds are usually compounds are usually between metals and between metals and nonmetals (opposite ends nonmetals (opposite ends of the periodic table).of the periodic table).

11Comparison

Ionic Compounds

• Crystalline solids (made of ions)

• High melting and boiling points

• Conduct electricity when melted

• Many soluble in water but not in nonpolar liquid

• Metal and nonmetals bond

Covalent Compounds

• Gases, liquids, or solids (made of molecules)

• Low melting and boiling points

• Poor electrical conductors in all phases

• Many soluble in nonpolar liquids but not in water

• Nonmetals bond with other nonmetals

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13

14

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A chemical bond in which two or more electrons are shared by two atoms.

How should two atoms share electrons?

F F+

7e- 7e-

F F

8e- 8e-

F F

F F

Lewis structure of F2

lone pairslone pairs

lone pairslone pairs

single covalent bond

single covalent bond

Covalent Bond

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8e-

H HO+ + OH H O HHor

2e- 2e-

Lewis structure of water

Double bond – two atoms share two pairs of electrons

single covalent bonds

O C O or O C O

8e- 8e-8e-double bonds double bonds

Triple bond – two atoms share three pairs of electrons

N N8e-8e-

N N

triple bondtriple bond

or

17PolarityPolarity

AA molecule, such as HF, that has a center of molecule, such as HF, that has a center of positive charge and a center of negative positive charge and a center of negative charge is said to be polar, or to have a dipole charge is said to be polar, or to have a dipole moment.moment.

+

FH

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Dipole Moment

• Direction of the polar bond in a molecule.

• Arrow points toward the more electronegative atom.

H Cl + - Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

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H F

FH

Electrons are shared unequally

A covalent bond with greater electron density around one of the two atoms resulting in partial charges (dipole)

electron richregionelectron poor

region

e- riche- poor

+ -

Polar Covalent 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 oil and water will not mix! Oil This is why oil and water will not mix! Oil is nonpolar, and water is polar.is nonpolar, and water is polar.

• The two will repel each other, and so you The two will repel each other, and so you can not dissolve one in the othercan not dissolve one in the 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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Determining Molecular Polarity

• Nonpolar Molecules

-Electrons are shared equally-Symmetrical electron density-Often identical atoms-Dipole moments are symmetrical and cancel out.

BF3

F

F F

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......

Polar Bonds

H Cl

Polar

A molecule has a zero dipole moment because their dipoles cancel one another.

H HO

PolarF F

B

F

Nonpolar

HH

H

N

Polar

Polar Nonpolar

F FCl

F

F F

Xe

F FCl

ClC

Cl

Nonpolar Polar

Cl

HC

Cl

H

H

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Hydrogen Bonding

• Occurs with polar structures only

• Includes a positive Hydrogen ion bonding directly to a negative ion

• Examples: H-O H-N H-F H2O

• DNA, RNA, and enzymes have many Hydrogen bonding sites

• Strongest intermolecular force

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London Dispersion forces

• Also known as van der Waals bonds

• Occur only with nonpolar structures

• Weakest intermolecular force

• Electrostatic bonds between atoms or molecules

• Temporary dipole moment

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Lewis Dot Bonding

• Write down examples on board

28Double and Double and even triple even triple bonds are bonds are commonly commonly observed for C, observed for C, N, P, O, and SN, P, O, and S

••O OC

•• ••

••

••O OC

•• ••

••

HH22COCO

SOSO33

CC22FF44

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1/25/10MONDAY

• Bell Ringer:

–Pick up the Molecular Geometry packet off the front green demo table.

–Remember, we needs Dots candy and toothpicks if you want to perform the edible lab

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MOLECULAR MOLECULAR GEOMETRYGEOMETRY

MOLECULAR MOLECULAR GEOMETRYGEOMETRY

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VSEPRVSEPR • VValence alence SShell hell EElectron lectron PPair air

RRepulsion theory.epulsion theory.

• Most important factor in Most important factor in determining geometry is determining geometry is relative relative repulsion between repulsion between electron pairs.electron pairs.

Molecule adopts Molecule adopts the shape that the shape that minimizes the minimizes the electron pair electron pair repulsions.repulsions.

Molecule adopts Molecule adopts the shape that the shape that minimizes the minimizes the electron pair electron pair repulsions.repulsions.

MOLECULAR GEOMETRYMOLECULAR GEOMETRYMOLECULAR GEOMETRYMOLECULAR GEOMETRY

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Some Common GeometriesSome Common Geometries

LinearLinear

Trigonal PlanarTrigonal Planar TetrahedralTetrahedral

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Other VSEPR chartsOther VSEPR charts

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Structure Determination by Structure Determination by VSEPRVSEPR

Structure Determination by Structure Determination by VSEPRVSEPR

Water, HWater, H22OOThe electron pair The electron pair geometry is geometry is TETRAHEDRALTETRAHEDRAL

The electron pair The electron pair geometry is geometry is TETRAHEDRALTETRAHEDRAL

The molecular The molecular geometry is geometry is BENTBENT..

The molecular The molecular geometry is geometry is BENTBENT..

H O H••

••

H O H••

••

2 bond 2 bond pairspairs

2 lone 2 lone pairspairs

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Structure Structure Determination by Determination by

VSEPRVSEPR

Structure Structure Determination by Determination by

VSEPRVSEPRAmmonia, NHAmmonia, NH33

The electron pair geometry is tetrahedral.The electron pair geometry is tetrahedral.

H

H

H

lone pair of electronsin tetrahedral position

N

The The MOLECULAR GEOMETRYMOLECULAR GEOMETRY — the — the positions of the atoms — is positions of the atoms — is TRIGONAL TRIGONAL PYRAMIDPYRAMID..

The The MOLECULAR GEOMETRYMOLECULAR GEOMETRY — the — the positions of the atoms — is positions of the atoms — is TRIGONAL TRIGONAL PYRAMIDPYRAMID..