Enloe Chemistry Name:_____________________________Unit 6 Date:_______________Period:_________

Molecular Geometry

Objectives

1. (1.2.1)Compare ionic, covalent and metallic bonds2. (1.2.5) Describe macromolecules and network solids as a class of molecules with unique properties due to

their intermolecular structure. ( ice, graphite/diamond, polymers(PVC, nylon), proteins( hair, DNA)3. (1.2.2)Infer the type of bond formed between any two elements.4. (1.2.5)Compare the properties of MP, BP, color, electrical conductivity, luster, brittleness, malleability,

ductility and physical state in ionic, covalent, metallic, and network compounds.5. (1.2.1)Construct (draw) Lewis dot diagrams for diatomic elements, H2O, NH3, CH4, H2S, CO, CO2,

NO31-

, CO32-, OH1-, BH3, PH3, HCl, HCN, NaOH, KCl, AlCl3 , CaF2, Na2SO4

6. (1.2.3)Determine the relationship between bond energy and bond length of single, double, and triple bonds.7. (1.2.2) Construct (draw) Lewis structures to predict the empirical formula for the following ionic

compounds: Compound formed with a) Ag+ and S2- b) Fe3+ and Cl- c) Fe3+ and O2-

8. (1.2.5) Define Valence Shell Electron Pair Repulsion Theory (VSEPR) and use it to predict bond angles and visualize the shape of the molecule for these electron pair geometries:a) linear b) trigonal planar c) tetrahedral

9. (1.2.5) Apply Valence Shell Electron Pair Repulsion Theory (VSEPR) to predict bond angles and visualize these molecular geometries: a) linear b) trigonal planar: i) trigonal planar ii) bent c) tetrahedral: i) tetrahedral ii) trigonal pyramidal iii) bent

10. (1.2.5) Define polar covalent bond and nonpolar covalent bond. Use electronegativity difference to classify covalent bonds as polar, nonpolar, or ionic.

11. (1.2.5) Identify molecules as polar or nonpolar based on their shape and the nature of their covalent bonds.12. (1.2.3) Define inter – particle and intra – particle forces. List and define 3 examples of each.13. (1.2.3) Cite evidence that intermolecular forces are weaker than ionic, covalent, or metallic bonds14. (1.2.3) Cite evidence that hydrogen bonds are stronger than dipole- dipole forces which are stronger than

dispersion forces in molecules of similar molecular weight.

Assignment 1: Bond Types

1. Chemical bond is a strong attachment between two atoms or ions.a. Three general types of chemical bonds:

i. Ionic bond-electrostatic force that exists between ions of opposite charge; formed from atoms by the transfer of one or more electrons from one atom to another.

ii. Covalent bond – sharing of electrons between two atomsiii. Metallic bond – each atom in a metal is bonded to several neighboring atoms; bonding

electrons are relatively free to move throughout the three – dimensional structure of the metal.

b. Comparing properties of Ionic Compounds, Covalent compounds and Metals.2. Inferring types of bonds.

a. Typically and ______________ form ionic bonds.b. Atoms of ________________ form covalent bonds.c. Predict the type of bond that forms between the following elements. Use their location on the

periodic table to make your prediction.i. Na-Fii. Cu-O

iii. H-Fiv. Si-Clv. Ag-Ag

vi. Al-Clvii. Pb-Cl

viii. Cu-Cuix. H-Ox. Ca-I

xi. K-Brxii. S-O

xiii. H-Hxiv. Cu-Ni

3. Ionic Compounds and Covalent Compounds.a. Ionic Compounds are compounds that are composed of cations and anions that are held

together by an electrostatic forces of attraction. b. Covalent (or Molecular) Compounds are compounds that are composed of atoms that are held

together by covalent bonds.

Assignment 2: Comparing properties of Ionic Compounds, Covalent compounds and Metals.

Ionic Compounds Covalent Molecules MetalsMelting Point All are ______ at 25°C

All have very high melting points due to the crystalline nature

NaCl 801°CCsF 683°CNaF 992°CMgO 2800°C

_____, ______ and ______ at 25°C

Very Wide range:H2 -259°CCH4 -184°CH2O O°C

C8H10N4O2

Caffeine, 238°C

All except Hg are _____ at 25°C

Fr 27° CHg -38°CFe 1535°CW 3410°CSn 232°C

CovalentNetworkSolidsall are ______ at 25°CSiO2 1700°CDiamond 3550°C

Boiling Point

Substances with high melting points have even higher boiling points

Extremely ______

NaCl 1413°C

MgO 3600°C

Generally _____

H2 -253°CCH4 -161°CH2O 10O°CC8H10N4O2

Caffeine, not available

Most areExtremely _____

Hg 357°C

Fe2861°C

W 5555°C

Sn 2602°C

Brittle Solid? Yes Some are: ice, sugar

Some Covalent network solids are extremely hard

No

Malleable and/or ductile?

None Some are: rubber, plastics, wax

Yes

Occur as gases at 25⁰C

None Some : H2, N2, O2, F2, Cl2, H2O, CO2, NH3, CH4,

small, low massmolecules

(MW<100amu)

None

OTHER INFORMATION

1) Ionic and metallic bonds tend to be very strong as indicated by the high melting points. However, since ionic compounds and metals do not exist as single discrete molecules, the comparison between ionic and metallic bonds vs. covalent bonds is flawed.

2) Electricity is conducted by moving charges. The metallic bond is a sea of constantly moving electrons that move throughout the metal. Ionic compounds separate into positive and negative ions when they dissolve in water. Metals, aqueous ionic comopound, and molten ionic compounds provide the moving charges necessary to conduct electricity.

3) Metals are shiny ( have luster ) because their outer electrons (valence) are not attached to any particular atom. Hence, they are free to wander throughout the material with little resistance. So when light shines on metal it sets these free electrons into vibration. Instead of energy springing from atom to atom, it's reemitted as visible light.

4) The malleability and ductility of metals are possible because metallic bonding is the same in all directions throughout the solid. One plane of atoms in a metal can slide past another without encountering any resistance or breaking any bonds.

4. Describe macromolecules and network solids as a class of molecules with unique properties due to their intermolecular structure. (ice, graphite/diamond, polymers(PVC, nylon), proteins( hair, DNA)

Assignment 3: Lewis Structures

1. How is a shared pair of electrons often represented?

2. How is a lone (nonbonding) pair of electrons represented?

3. What is the octet rule?

4. Comparing characteristics of single, double, and triple covalent bonds:

5. Draw Lewis dot diagrams for the following:

Se Cl Al C

Ca Na P Ne

6. The Lewis dot diagrams predict that:a. 7A elements will form _____________ covalent bond.

b. 6A elements will form _____________ covalent bonds.

c. 5A elements will form _____________ covalent bonds.

d. 4A elements will form _____________ covalent bonds.

e. Hydrogen and Fluorine will always form only ____ covalent bond and will always be terminal.

Assignment 4: Drawing Lewis Structures for Covalent Compounds

Use the following process to draw Lewis structures for covalent compounds.

1. Find the total number of valence shell electrons (vse) from all atoms.

2. Write the symbols for the atoms to show which atoms are attached to which and connect each atom with 2 shared electrons.a. When a central atom has a group of other atoms bonded to it, we usually write the central atom first,

as in CH4 or SO4 2- .b. In oxyacids such as H2SO4 or HClO3, the hydrogen is always bonded to an oxygen, and the other

element is the central atom.c. In a molecule like HCN, the atoms are written in the order in which they are bonded.d. In hydrocarbons, like C2H6, the Carbon atoms are attached to each other.

3. Complete the octets of the atoms bonded to the central atom. a. Remember that hydrogen can only share 2 electrons and form 1 bond.b. Boron will not form a double or triple bond. It is “happy” with 6 electrons.c. If the central does not have

4. Place any leftover electrons on the central atom.

5. If there are not enough electrons to give the central atom an octet, try double or triple bonds.

Problems: Draw Lewis structures for the following molecules and polyatomic ions.

6. H2

7. Cl2

8. O2

9. N2

10. H2O

11. O3

12. NH3

13. CH4

14. CO

15. CO2

16. CO32-

17. HCl

18. PCl3

19. H2S

20. NF3

21. C2H6

22. C2H4

23. C2H2

24. HClO

25. HNO3

26. SO3

27. H2CO3

28. HCN

29. BH3

30. ONCl

31. NH4 +

32. OH1-

33. BrO31-

Assignment 5: Drawing Lewis Structures for Ionic CompoundsUse the following process to draw Lewis structures for ionic compounds.

1. Write as many of each element symbol as indicated in the chemical formula. Include their most likely charge.

2. Draw the Lewis Dot Diagram for each element around each symbol. Use “x” for the electrons around the anion.

3. Show the transfer of electrons from the cation to the anion by using arrows.

4. Write the final lewis structure for the ionic compound: a. Use coefficients to indicate the number of each ion needed. b. Place brackets around the anion with the charge inside the brackets.c. Represent transferred electrons as dots and electrons present before transfer as “x.”d. No electrons should be represented for the cation.

Problems1. NaCl

2. K2S

3. AlCl3

4. CaF2

5. Al2O3

Assignment 6: Valence Shell Electron Pair Repulsion

1. Predicts the molecular shape of a bonded molecule2. Unshared pairs of electrons (nonbonding electrons/lone pairs) on the central atom repel the most. 3. All pairs of electrons (bonded or non-bonded) repel each other around the central atom. 4. Count the number of electron domains (sites where there are bonded or non-bonded electrons)5. Electrons around the central atom arrange themselves as far apart from each other as possible6. Bonded electrons (single, double, or triple bonds) count as one domain.

Assignment 7: VSEPR Practice Problems

1. What is the characteristic electron domain geometry associated with the following number of electron domains about a central atom?a. 2 electron domains is _______________________

b. 3 electron domains is _______________________

c. 4 electron domains is _______________________

2. What is the electron domain geometry and the molecular geometry of each of the following?a. CH4 electron domain geometry is ______________ and the molecular geometry is _______________.

b. H2O electron domain geometry is ______________ and the molecular geometry is _______________.

c. CO2 electron domain geometry is ______________ and the molecular geometry is _______________.

2. What is the molecular geometry of a molecule that has:a. two bonding domain and one nonbonding domain of electrons on the central atom

b. three bonding domains and one nonbonding domain of electrons on the central atom

c. two bonding domains and two nonbonding domains of electrons on the central atom

d. three bonding domains and no nonbonding domains

e. four bonding domains and no nonbonding domains

3. Arrange the following molecules in order of increasing bond angle:a. CH4, CO2, BH3

b. BH3, O3

c. H2O, CH4, NH3

d. C2H6, C2H2, C2H4

Homework: Identify the shape (molecular geometry) of each molecule or ion for which you drew the Lewis structure in Assignment 2.

Assignment 8: Bond Polarity

1. Ionic – transfer of electrons from one atom to another.2. Covalent - sharing of e- between atoms3. nonpolar covalent – equal sharing of e-4. polar covalent – unequal sharing of e-

5. If one end of a molecule is slightly positive and another end is slightly negative the molecule is polar. It is called a dipole because it has a dipole moment.

6. A dipole moment only occurs in molecules that have __________ ________ and/or one or more ________ _________ of electrons on the central atom.

7. A polar molecule has separate centers of __________ and _________ charge. This is why polar molecules are known as dipoles.e. Symmetrical molecules (no lone pairs on the central atom) with all atoms surrounding the central atom

the same are non-polar. Any molecule that is tetrahedral, trigonal planar or linear with all surrounding atoms the same will be non-polar.

f. Any molecule with one or more lone pairs on the central atom is polar

Homework: Describe each molecule drawn in assignment 2 as polar or non-polar.