Please help me with this AP chemistry question!!?

Question

Account for each of the following observations abotu pairs of substances in your answers, uses appropriate principles of chemical bonding and or intermolecular forces. In each part, your answers must include references to both substances.

a.) Even though NH3 and CH4 have similar molecular masses, NH3 has a uch higher normal boiling point(-33 degrees C) than CH4 (-164 degrees C)

b. At 25 degrees C and 1.0 atm, ethane (C2H6) is a gas and hexane (C6H14) is a liquid.

c. Si melts at a much higher temperature (1410 degrees C) than Cl2 (-101 degrees C)

d. the melting point of NaF is 993 degrees C, whereas the melting point of CsCl is 645 degrees C/

Answer 1

a) NH3 is a polar molecule while CH4 is not. Polar molecules experience dipole-dipole forces which are stronger attractive forces and hold them together until a higher temperature is reached.

b) Hexane has a higher molecular mass and experiences more London dispersion forces than the lighter ethane.

c) Silicon is a network solid held together by strong covalent bonds. Chlorine is a molecular gas with no bonding between the diatomic molecules of the gas.

d) Sodium fluoride is composed of smaller ions. These smaller ions fit closer together and are held stronger by the opposite charges. In other words, the charged ions can get closer so the attraction is larger. CsCl is composed of larger ions. The attraction they feel is less due to the larger ions.

Answer 2

a NH3 is polar and CH4 is not. NHs has the extra pair of unshared electrons. The polarity gives it a higher boiling point

b. Higher mass usually means higher boiling point due to increased bonds. This is the case here even though both are non polar

c. Cl2 is a non polar molecule and the bonds are held weakly together. Therfore, low boiling point. Si is an element with a strong lattce structure. Hard to pull apart to melt.

d. The ionic bond (EN diff) in NaF is much higher than in CsCl. Thus the bond attraction is stronger, means higher melting point

Answer 3

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