Van Der Waals Forces

PRACTICE TEST – Inter Molecular Forces Name: __Answer Key______Identify each as either ionic or covalent compounds and provide either the name or formula 6 points

You may find these prefixes mono- di- tri- tetra- penta hexa- hepta octa- nona- deca- helpful for the questions below 1 2 3 4 5 6 7 8 9 10 Name or Formula Ionic or Cation & Anion Name or Formula Covalent

ex) nitrogen trihydride Covalent N/A - Covalent NH3 (also known as ammonia) 1+ 2- ex) (NH4)2CO3 Ionic 2 NH4 1 CO3 Ammonium Carbonate 2+ 1- 1) calcium hydroxide Ionic 1 Ca 2 OH Ca(OH)2 2) CO Covalent N/A Carbon Monoxide

3) carbon tetrahydride Covalent N/A CH4 3+ 1- 4) Iron (III) Nitrate Ionic 1 Fe 3 NO3 Fe(NO3)3 2+ 2- 5) MgSO4 Ionic 1 Mg 1 SO4 Magnesium Sulfate 2+ 1- 6) Co(OH)2 Ionic 1 Co 2 OH Cobalt (II) Hydroxide Ionic compounds need to have a Net Charge of ZERO

Identify each of the Bond Types as either: Nonpolar Covalent, Polar Covalent, or Ionic (Do not forget to include the identification of cations and anions or partial positive and partial negative where appropriate.) (for ionic) (for polar covalent) 6 points 7) HO H O Δ EN = 8) HI H I ΔEN = 2.2 3.5 1.3 2.2 2.5 0.3 Polar Covalent Nonpolar Covalent (Identification) (Bond Type) (Identification) (Bond Type) 9) (+) MgO (-) Ionic 11) HF Polar Covalent 10) NH Polar Covalent 12) O-O Nonpolar covalent

13) Draw the Lewis Structure of CH3OH (Use the box below – remember to draw your circles) 2 points

14) Based on the four structures below, x H x H x H x circle the molecular structure of CH3OH C H O 1 point a) c) H x H x C H b) d) x Ox H

Draw the following molecules and identify each as a polar molecule or a nonpolar molecule. If the molecule is polar, be sure to draw any dipoles that are created. (I need to see some work) 3 points

15) H-Br 16) CClCl4 17) NH3 H H Br Cl C Cl N H 2.2 2.8 2.5 3.0 3.0 2.2 Cl H Polar Nonpolar Polar 18) For a compound to be classified as an electrolyte, what must happen when it dissolves in water? 2 points The compound must be able to conduct electricity - when dissolved, the compound become ions (which are charged particles). These charged particles can conduct the electricity through the water.

Match each item (a-o) with the correct statement below. 10 points (NOTE: each item (a-o) may be used once, more than once, or not at all).

a. cation f. ionic bond l. Van der Waals force b. anion g. polar covalent bond m. London dispersion force (LDF) c. electrostatic force h. nonpolar covalent bond n. dipole-dipole interaction (DDI) d. electronegativity j. intramolecular force o. hydrogen bond (HF) e. dipole (polar molecule) k. intermolecular force

_c_ 19. the force of attraction between a positive and negative charge _j_ 20. the electrostatic force between atoms – (covalent bond between atoms) _k_ 21. the electrostatic force between molecules – cause molecules to stick to each other _a_ 22. atom or group of atoms having a positive charge _n_ 23. intermolecular force between molecules that have permanent dipoles that are attracted to each other _d_ 24. the relative ability of a bonded atom of an element to attract the electrons from the another element participating in the bond. _e_ 25. a molecule that has two electrically charged regions (a slightly positive region and a slightly negative region) _m_ 26. these forces are present in all molecules, whether they are polar or nonpolar. _f_ 27. the electrostatic force of attraction binding oppositely charged ions together _g_ 28. a covalent bond between two atoms of significantly different electronegativities – (bonding occurs when the electrons are shared unequally.) _b_ 29. atom or group of atoms having a negative charge _h_ 30. a covalent bond between atoms where the bonding electrons are shared equally. _m_ 31. intermolecular force between an instantaneous dipole and an induced dipole. (Caused by the motion of the electrons)

_o_ 32. this type of intermolecular force is found between molecules of water (H2O) _o_ 33. the dipole-dipole interactions experienced when H is bonded to N, O, or F _d_ 34. in a polar covalent bond, the atom with the higher ______will become partially negative _l__ 35. the weak attractive forces that hold molecules together (includes London dispersion, dipole-dipole interactions and hydrogen bonds) _c_ 36. the force of attraction within ionic, metallic, and covalent bonds, hydrogen bonds, dipole-dipole interactions, London dispersion forces, and even between protons & electrons is due to ______.

Identify each of the following as either intermolecular or intramolecular 4 points 37) _ intramolecular__ Polar Covalent Bond 40) _ intramolecular__ Ionic Bond 38) _ intermolecular__ Hydrogen Bond 41) _ intermolecular__ Dipole-Dipole Interact 39) _ intermolecular__ London Dispersion 42) _ intermolecular__ Van der Waals _a_ 43) Which of the following covalent bonds is the most polar? a. H—F b. H—C c. H—H d. H—N

_c_ 44) Which of the following atoms acquires the most negative charge in a covalent bond with hydrogen? a. C b. N c. O d. S

_b_ 45) Which of the forces of molecular attraction is the weakest? a. dipole-dipole interaction b. London dispersion c. hydrogen bond d. single covalent bond _d_ 46) Why do atoms share electrons in covalent bonds? a. to become ions and attract each other c. to become more polar b. to gain a higher electronegativity d. to attain a full valence energy level

_c_ 47) A bond formed between a silicon atom and an oxygen atom is likely to be ____. a. ionic b. coordinate covalent c. polar covalent d. nonpolar covalent

_b_ 48) What is thought to cause the London dispersion forces? a. attraction between ions c. sharing of electron pairs b. motion of electrons d. differences in electronegativity

_c_ 49) What causes Hydrogen bonds? a. sharing of electron pairs c. bonding of a covalently bonded hydrogen to an unshared electron pair b. attraction between ions d. attraction between polar molecules

_a_ 50) Why is hydrogen bonding only possible with hydrogen? a. Hydrogen’s nucleus is electron deficient when it bonds with an electronegative atom. b. Hydrogen is the only atom that is the same size as an oxygen atom. c. Hydrogen is the most electronegative element. d. Hydrogen tends to form covalent bonds.

Identify the primary type of Van der Waals Forces that exist between each type of molecule: LDF = London Dispersion Forces, DDI = Dipole-Dipole Interaction, HB = Hydrogen Bonds 10 points

51) C2H5OH- _HB__ 52) CH3Br- _LDF__

53) HI- _LDF__ 54) CCl4- _LDF__

55) CH3NH2 -_HB__ 56) CO2- _LDF__

57) Ar- _LDF__ 58) HF - _DDI__

59) C2H4O - _DDI__ 60) Br2- _LDF__

61) CH3Cl - _DDI__ 62) C3H8- _LDF__ 63) List and explain the two factors that affect the force of attraction in London dispersion forces? 2 points Size – the larger the molecule, the more electrons there are, the stronger the temporary dipole, the stronger the London dispersion force

Shape – long skinny molecules can allow for more surface area (surface contact) between molecules, the greater the contact (surface area), the stronger the London dispersion force.

64) Explain how London dispersion forces cause molecules to be attracted to one another. 2 points The motion of the electrons – the electrons can move so that most of the electrons are on one side, when this happens, these electrons create a partial negative side and the opposite side is missing electrons and becomes partial negative. This is called an instantaneous dipole. The instantaneous dipole can contact another adjacent molecule and induce a second dipole. The electrostatic force of attraction between the partial positive of one dipole is attracted to the partial negative of the second dipole – this is a London dispersion force (due to electron movement). .

65) Rank the following FOUR molecules from lowest to highest boiling points: EXPLAIN 2 points (1) (4) (3) (2) CH4 CBr4 CCl4 CF4 LDF LDF LDF LDF  All LDF

The larger the molecule, the stronger the LDF, the higher the boiling point

66) Rank the following THREE molecules from lowest to highest boiling points: EXPLAIN 2 points

 All LDF LDF (1) LDF (3) LDF (2) The larger the molecule, the stronger the LDF, the higher the boiling point

67) Rank the following THREE molecules from lowest to highest boiling points: EXPLAIN 2 points

DDI (2) HB (3) LDF (1)

LDF forces are the weakest, and HB are the strongest  stronger forces = higher boiling points

68) Explain “why” atoms become partially positive and partially negative in a polar bond. 2 points

In a polar bond, the difference between the electronegativities between the two non- metals is greater than 0.4, this difference will result in the shared electrons not being shared equally. This unequal sharing will cause the electrons to move closer to the atom with the higher electronegativity. The negatively charged electrons will result in this higher electronegative atom becoming partial negative, and the other atom becoming partial positive.