Covalent Bonding&

Intermolecular Forces

Covalent Bonding and Intermolecular ForcesConcepts to Master

• How can you use electronegativity to determine if a bond is covalent or ionic?

• What’s the difference between a compound and a molecule?

• What type of bond is formed when electrons are shared?

• Understand that ionic bonds form between a metal and a nonmetal where as covalent bonds form between two non-metals.

• What are the differences in physical and chemical properties between covalent molecules and ionic compounds?

• What is the difference between a single bond, double bond, and triple bond in a molecule?

• Give examples of molecules that have single, double, or triple bonds.

• Be able to draw Lewis Dot diagrams for covalent molecules.

• Be able to calculate formula mass and percent composition for covalent molecules.

• Be able to name covalent molecules when given the chemical formula.

• Be able to write the chemical formula when given the name of a covalent molecule.

• What is the difference between a polar bond and a nonpolar bond?

• Be able to determine the polarity of a bond and the polarity of a molecule.

• Understand that all the diatomic are nonpolar and covalent.

• How do molecular shapes indicate polarity?• How are network solids different from

molecular solids?• What are examples of intramolecular forces

and intermolecular forces?• Be able to rank the various intermolecular

forces and intramolecular forces according to bond strength.

• Give an example of a substance that would contain hydrogen bonds, dipole-dipole forces, or London dispersion forces.

• What is the relationship between molecule size and the strength of the London dispersion force?

• What is the relationship between polarity and the strength of the dipole-dipole forces?

• Why is water a unique molecule?

Vocab• Allotrope• Bent• Compound• Covalent• Dipole-dipole force• Electronegativity• Hydrogen bonding• Induced dipole-dipole forces• Intermolecular• Intramolecular• Ionic• Linear• London dispersion forces

• Metallic• Molecular solid• Molecule• Network solid• Non-polar• Polar• Tetrahedral• Trigonal planar • Trigonal pyramidal

Labs• Characteristics of Bonding• Lava Lamp• Evaporative Cooling• Shapes of Molecules

Elements and Electronegativity

• Table S in your reference booklet show the electronegativity value for each element (arbitrary scale 0-4).

• The electronegativity difference between the elements of a compound indicates the type of bond between the elements.

• If the difference is 1.7 or greater, the bond is IONIC.

• If the difference is less than 1.7, the bond is COVALENT

EN

(atom 1)

EN

(atom 2)

∆EN IONIC or COVALENT

K2O

CH4

SrBr2

PCl3

ZnO

Determining Bond Type

What other way can you tell if substance is ionic or covalent?

Covalent Substances (Molecular)

• A covalent molecule is a one in which the atoms share electrons.

• Covalent molecules are

formed when two

nonmetals bond to each other.

IN CONTRAST• In ionic

compounds electrons are completely transferred.

• Ionic compounds are formed when a metal combines with a nonmetal.

Ionic or Covalent or Both?

1. FeN _____

2. KCl _____

3. HI _____

4. CI4 _____

5. SO2 _____

6. NiPO4 _____

7. IF _____

8. SnCO3 _____

9. CCl4 _____

10.NH3 _____

11. I2 _____

12.NH4Br _____

13.NCl5 _____

14.H2 _____

15. Be(ClO2)2 _____

Covalent Properties(Physical or Chemical?)

• Covalent molecules generally have much lower melting and boiling points than ionic compounds.

• Covalent molecules are soft and squishy.

• Covalent molecules tend to be more flammable than ionic compounds.

• Covalent molecules don't conduct electricity in water.

• Covalent molecules do not usually dissolve in water.

• The electronegativity difference between the elements of a compound is less than 1.7.

Covalent Compounds• Remember the octet rule: all

atoms want 8 valence electrons.

• When metals bond to nonmetals, ionic compounds are formed because the metal atoms don't want electrons and easily give them to nonmetals that do want electrons.

• Nonmetals want electrons (remember, they have a high electronegativity). So when two nonmetals combine, they have to share electrons to satisfy the octet rule.

Forming Covalent Bonds• NONMETAL + NONMETAL• They share electrons. • Nonmetals share electrons to obey the octet rule:

all atoms want 8 valence electrons.

Diatomic!

Covalent Bond Formation

+ 4

(H2)

(CH4)

Covalent Compound Formation• Single Bonds shares 1 pair of electrons.

• Double Bonds share 2 pairs of electrons.

• Triple Bonds share 3 pairs of electrons

Cl Cl

O O

N N

Total # of Electrons = 2

Total # of Electrons = 6

Total # of Electrons = 4

Covalent Lewis Dot Diagrams

1. Count the TOTAL # of Valence electrons in the compound. (Count ALL)

2. Draw a “skeleton". (Draw)

3. Add electrons to “outside” atoms to achieve octet. (Outside atoms with 8)

4. Place any remaining electrons on the center atom. (Left overs on center)

5. If center atom does not have an octet, move nonbonding pairs to center atom. (Move nonbonding to center if needed)

6. Recount electrons and draw bonds. (Recount and draw bonding lines)

Covalent Lewis Dot Diagrams

• CH4

• CO2

• CS2

• PO4-3

1. Count all2. Draw3. Outside atom with 84. Left overs on center5. Move nonbonding to

center if needed6. Recount and draw

bonding lines

Molecule Electron Dot

SiH4

H2O

CBr4

HI

CHCl3

F2

Formula Mass& Percent Composition

• Calculate the same way for covalent molecules and for ionic compounds!

Naming Covalent Compounds

1. Name the first element

1. If there is more than one of these atoms, write the appropriate prefix before the element’s name.-first element-prefix-root of second element-"-ide" (the prefix "mono" is assumed, and therefore dropped).

2. Write the “root” of the second element

1. If there is more than one of these atoms, write the appropriate prefix before the root name

3. Add "-ide" to the end

4. Exceptions

1. H2O is water, not dihydrogen oxide

2. NH3 is ammonia, not nitrogen trihydride

3. CO is carbon monoxide, but in all other cases, the mono is dropped.

4. If there is more than one of these atoms, write the appropriate prefix before the element’s name.-first element-prefix-root of second element-"-ide" (the prefix "mono" is assumed, and therefore dropped).

Naming Covalent Compounds

Prefixes• Mono - 1 (the prefix

"mono" is often assumed, and therefore dropped).

• Di - 2 • Tri - 3 • Tetra - 4 • Pent - 5 • Hex - 6 • Hept - 7 • Oct - 8 • Non - 9 • Dec - 10

1. Examples:

1. SO2

2. Si3P6

3. NCl3

4. CO2

5. S5F

2. Answers:

1. sulfur dioxide

2. trisilicon hexaphosphide

3. nitrogen trichloride

4. carbon dioxide

5. pentasulfur fluoride

prefix-first element-prefix-root of second element-"-ide"

Naming Practice

• P4O10

• SF6

• Mg(C2H3O2)2

• (NH4)3PO4

• CCl4• N2O

• PBr3

Covalent Molecules ONLY!• Polar Covalent Molecule

is one where the electrons are UNEQUALLY shared between atoms within the molecule.

• Electrons are NOT EVENLY distributed throughout the molecule.

• Between atoms that are different!

• Non-polar Covalent Molecule is one where the electrons are EQUALLY shared between atoms within the molecule.

• Electrons are EVENLY distributed throughout the molecule.

• Often between like atoms!

Iodine

• Iodine forms a diatomic non-polar covalent molecule.

• The graphic on the top right shows that iodine has 7 electrons in the outer shell. Since 8 electrons are needed for an octet, two iodine atoms EQUALLY share 2 electrons.

Polar Molecules

Which atom seem to pull harder on the electrons and why?

Ammonia Water

HydrofluoricAcid

NonPolar Molecules

Which atom seem to pull harder on the electrons and why?

Carbon Tetrachloride

Carbon Dioxide

Fluorine Molecule

ALL Diatomics are NONPOLAR!

Polar or Non-Polar?

Shapes of MoleculesWhich ones are polar or nonpolar?

Solubility and Polarity• Like dissolves like!

– Polar solutes dissolve in polar solvents

– Ions dissolve in polar solvents

– Nonpolar solutes dissolve in nonpolar solvents

Intermolecular Forces

• Force of attraction or repulsion between Covalent Molecules.

• Do NOT apply to Ionic Compounds!

• NOT the bond between atoms, but the force between molecules.

• The further apart the molecules are, the weaker the intermolecular force.

Phases of Matter and Attraction

Attraction increases between molecules

Attraction decreases between molecules

Intramolecular Forces are much

stronger than Intermolecular Forces

Intermolecular Forces

• The physical properties of melting point, boiling point, viscosity, surface tension, and solubility are related to the strength of attractive forces between molecules. These attractive forces are called Intermolecular Forces. The amount of "stick togetherness" is important in the interpretation of the various properties listed above.– The stronger the “stick togetherness” or BOND, the higher the MP, BP,

viscosity, and surface tension.

– The stronger the “stick togetherness” or BOND, the less soluble the substance will be.

• There are four types of intermolecular forces.– Ionic forces (electrostatic forces between ions)

– Dipole forces

– Hydrogen Bonding

– Induced Dipole Forces (London Dispersion Forces)

Hydrogen Bonds

• The Strongest Intermolecular Force!

• When the molecules contain hydrogens that are attached to either N, O, or F, hydrogen bonding occurs BETWEEN those MOLECULES.

• Opposites attract.

Dipole Forces• Polar covalent molecules

are sometimes described as "dipoles", meaning that the molecule has two "poles".– One end (pole) = partial

positive charge – Other end (pole) = partial

negative charge. – The molecules will

orientate themselves so that the opposite charges attract each other.

Induced Dipole Forces(London Dispersion Forces)

• Forces between non-polar molecules are the weakest of all intermolecular forces.

• "Temporary dipoles" – Formed by the shifting of

electron clouds within molecules.

– These temporary dipoles attract or repel the electron clouds of nearby non-polar molecules.

• Exist for only a fraction of a second

• The strength of induced dipole forces depends on atomic size and distance between molecules. – Bigger atoms exert a bigger

force– Farther apart exert less force.

Ranking Intermolecular Attractions

• Attractions between molecules that are hydrogen bonded are the strongest. (hydrogens are bonded to N, O, F)

• Attractions between molecules that are polar covalent are strong. (hydrogens if present are NOT bonded to N, O, F)

• Attractions between molecules that are nonpolar covalent are weak.

Ionic Bonds (electrostatic forces) >Covalent Bonds >Hydrogen Bonding >Dipole-Dipole Attractions >Induced Dipole DipoleForces

Rank the following from weakest to strongest intermolecular attractions.

1. Determine if the molecule is polar or nonpolar.

2. If it’s polar and hydrogens are present, determine if they are connected to a N, O, or F.

3. Hydrogen bonding is strongest, polar covalent attractions are strong, nonpolar covalent attractions are weak.

• HCl• H2O• CBr4

Intermolecular Forces and Physical Properties

• If intermolecular forces are strong the molecules are harder to pull apart so…– It takes more energy

to melt the substance and MP is higher

– It takes more energy to boil the substance and BP is higher

• If intermolecular forces are weak the molecules are easier to pull apart so…– It takes less energy to

melt the substance and MP is lower

– It takes less energy to boil the substance and BP is lower

Which has the strongest intermolecular forces?

• Substance with BP of 100oC• Substance with BP of 2300oC• Substance with BP of 212oC• Substance with BP of 0oC

• Solid at 23oC• Liquid at 23oC• Gas at 23oC

• Solid that melts at 10oC • Solid that melts at 0oC • Solid that melts at -10oC • Solid that melts at -20oC

Why does soap remove dirt from clothes? Soap has two ends!

• Hydrophobic– Hates water!– Nonpolar!

• Hydrophilic– Loves water!– Polar!

Why does soap remove dirt from clothes? Due to its Intermolecular Attractions and like dissolves like!