Why is water so unique?

Why Can water bugs run across a pond?

Why does water have such a high boiling point?

Why can we live on earth?

Why is water attracted to a – charge?Why is Hexane not attracted?

In this unit we will be able to understand how the Chemical

Bonds in a substance determine physical properties

• Why water is so unique• How the bonds that compose a substance

determine the properties within• How shampoo works• How household cleaners work effectively

Lets set up your Lab Book

• Purpose: To study the physical properties of common solids and to investigate the relationship between the type of bonding in a substance and its properties.– Volatility– Melting Point– Solubility– Brittleness– Conductivity

• Procedure: See Handout• Volatility-Waft the substance• Solubility (Hexane and Water) in well plate

• Conductivity (RED &GREEN LIGHT MEANS CONDUCTIVE)

• Melting Point Watch Glass on beaker of water and test tube in bunsen burner

• Brittleness (MORTAR AND PESTLE STATION)

Data

• Record Observations in Table

Disposal

• Rescue Aluminum if possible• Rinse out Sand in Garbage• Everything else can go down Sink

What did you discover in the periodic properties lab?

• Which substance was the most volatile?• Which substances had the lowest melting

point?• Which substances conducted electricity?• Which substances dissolved in water? Hexane?• Which substances do you believe had the

strongest bonds? Why?• Which substances do you believe have the

weakest bonds? Why?

• How do you determine the types of bond that exist in a compound?

• What is electronegativity?• For the following molecules,and ionic

compounds• Draw the Lewis Dot Structure

• CaS• AlCl3

• BH3

Electron dot drawings for polyatomic ions

Always include brackets and charges, but have covalent bonds inside the ion

Count the number of valence electrons for each and the add or subtract and electron to make the correct charge

NH4+

OH-

SO42-

Draw NH4OH

Exceptions to the octet rule1. Metals

MgH2

BH3

3. Some Nonmetal atoms because of their size, they can have more than an

octet of electrons (due to the presence of empty “d” orbitals which can be used for bonding).

SF6

PCl5

DON’T FOCUS ON THESE BUT KNOW THEY OCCUR!

Try these….

• Mg(OH)2 C3H6 O2

Note:

• Not all covalent bonds have equal sharing of electrons

• There are electron hogs!!! Elements that hold on to the electrons more tightly than others

• You can determine if a bond is ionic,covalent and if there is an electron hogs, through looking at a characteristic property.

When the ΔE.N. is less than 2.0, the bond is covalentExamples: The O-H Bond in H2O

The N-O Bond in NO2

• This means the electrons spend more time around one of the elements giving it a partial charge

• Draw a picture of how you think the electrons would be distributed for an OH bond and a NO bond

When the electrons are shared equallyex: H-H bond NCl Bondthe bond is pure covalent and has no partial charge

Draw a picture that describes what this would look like

Why do you think there would not be a partial charge on these bonds?

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

atoms that are going together.atoms that are going together.

Electronegativity Difference• If the difference in electronegativities is

between:– 2.0 to 4.0: Ionic– Covalent Bonds– 0.1 to 1.9: Polar Covalent– 0.0: Non-Polar Covalent

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

These bonds are called intramolecular forces

• Have various strengths– Ionic (STRONGEST)– Polar Covalent (NEXT STRONGEST)– Covalent (STRENGHTH DEPENDS ON

ELECTRONEGATIVITY DIFFERENCE)

Bond PolarityBond PolarityBond PolarityBond Polarity

HCl 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 slight and H has slight positive charge positive charge (+ (+ ))

H Cl••

••

+ -••H Cl

••

••

+ -••

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

Glucose is charged thus will be attracted to the charged bonds in water

Bond PolarityBond PolarityBond PolarityBond Polarity

Bond PolarityBond PolarityBond PolarityBond Polarity

• ““Like Dissolves Like”Like Dissolves Like”– Polar dissolves PolarPolar dissolves Polar– Nonpolar dissolves Nonpolar dissolves

NonpolarNonpolar

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).

Intermolecular Forces and

Bonding in Solids

“Measure” of

intermolecular force

boiling point

melting point

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.

Types of intermolecular Forces• Dispersion Forces

Weak Intermolecular Forces• Dipole-dipole interactions • Hydrogen bonds (Bonds between H and F,O,N Ex:

H2O, NH3

• Relative strength of Intermolecular Forces: • Weakest to strongest: dispersion forces, dipole-

dipole, hydrogen bonds• All are much weaker than intramolecular forces

(covalent bonds,ionic bonds or metallic bonds)

What type of Intermolecular Forces exist

• In Non Polar molecules• Dispersion Forces

• In Polar Molecules• Dipole Dipole Forces, dispersion forces and sometimes

Hydrogen Bonds

SO O

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

HF

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

• Relative StrengthDispersion forces are the weakest intermolecular force (one hundredth-one thousandth the strength of a covalent bond), hydrogen bonds are the strongest intermolecular force (about one-tenth the strength of a covalent bond).

How does mass affect dispersion forces?

Boiling Points of Group IV Hydrides

Which molecule will have a lower boiling point?

AsH3 or PH3? Why?

Why does water have the qualities that it does?

• What types of bonds?• What types of intermolecular forces at room

temperature?• Why types of substances will dissove in water?• Will NaCl dissolve in water?• Will NaCl dissove in hexane?• Will Lauric acid dissolve in water?• Will Lauric acide dissolve in hexane?

The difference between polar bonds and polar molecules

• Polar bonds have a electronegativity difference between 2 atoms

• Polar molecules– Include a polar bond– Have an asymmetrical shape

• Is NH3 a Polar Molecule?– Yes! Why?

Is CCl4 a polar molecule? Why?

Does it have a polar Bond? YesDo it have an asymmetrical shape? NO!!!Thus it is not a polar molecule.

What about CO2

Does it have a polar bond?Is it asymmetrical? NOThus it is not a polar molecule..