Lewis Structures
The molecular geometry of the compound CH4
Tetrahedral, 109.5o
Why the dipole arrow points towards Fluorine in the molecular compound HF.
Fluorine is more electronegative, so it will pull electrons closer to it creating a partial negative charge.
How does sodium fluoride conduct electricity?
Sodium fluoride is ionic, will conduct when particles are free to move (+/- ions). This occurs when dissolved in water or molten.
Often referred to as a “bond” but it does not actually occur within a molecule.
Hydrogen “bonding”
The molecular geometry AND bond angles of NH3
Trigonal pyramid.
<109.5o or 107o
The reason why SO2 is more soluble in water than CH4.
SO2 is polar due to the lone pairs on the sulfur. This negative dipole will be attracted to the positive dipole on the hydrogens of water.
This is the reason why ionic compounds have a high melting point.
Strong electrostatic forces between ions. This required a large amount of energy to break these bonds.
The electron cloud of HF is smaller than that of F2 , however, HF has a much higher boiling point than F2. Explain why
The hydrogen bonding interactions in HF are much stronger than the weak dispersion forces between F2 molecules.
The molecular geometry of AND bond angles SF4
Seesaw, 90o & 120o
Give an example of a nonpolar molecule with polar bonds.
CH4, SF6, CO2 etc
Typically, metals are both malleable and ductile. What is the best explanation for these properties?
In metals the electrons are free flowing and form nondirectional bonds.
Four different liquid compounds in flasks at 20°C. Flask A has 1% in the gas phase, Flask has 5% in the gas phase, and Flask C has 10% in the gas phase. What can be said about the intermolecular forces of the molecules in flask C?
Flask C contains the weakest interactions between molecules. Weaker interactions between molecules in a liquid result in a larger fraction of molecules having enough energy to overcome the intermolecular forces and escape to the vapor phase. This results in more particles in vapor phase and a higher vapor pressure.
The bonding orbitals of Sulfur AND oxygen in SO2.
Sulfur- sp2
Oxygen- sp2 or sp3
The property responsible for ethane CH3CH3 being a gas whereas hydrazine N2H4 is a liquid at room temperature.
What is N2H4 is polar. This means it experiences dipole-dipole IMF while ethane has weaker LDF. Hydrazine would have a stronger force of attraction needing more energy to pull the molecules apart and thus evaporate.
Which structure SeF2O or SeF2O2 has the strongest bond energy of the Se-to-O bond?
The bond in structure D is a double bond, which has a greater energy compared to the bond in structure A, which is a single bond. (It requires more energy to break a than a single bond.)
How are dipole-dipole interactions different from dispersion forces?
London dispersion forces are weaker than dipole-dipole interactions. LDF experiences weak temporary dipoles while dipole-dipoles has permanent dipoles.
Draw the most Likely Structure of NCS-1
[N = C = S]-1 (lone pairs not shown)
Zero formal charge on C & S. Most electronegative atom as the nonzero formal charge.
In reverse phase chromatography (polar solvent) compound A is found to have an rf value of 0.8 and compound B has an rf value of 0.5. What can be said about compound A?
Compound A is polar. Reverse Phase chromatography, mobile phase = polar. High rf value means compound A was more attracted to the mobile phase so it is more polar.
Although the molar mass of KCl is greater than that of KF , the density of KCl is actually less than that of KF . Based on atomic properties explain this phenomenon?
Chloride ions are larger than the fluoride ions, which causes the interionic distances in the solid to increase to the point where the effect of the larger spacing among ions in KCl is greater than the effect of the larger mass of the chlorine on the density.
Increase in CO2 pollution has caused the ocean to increase in acidity. How is CO2 soluble in water?
Dipole- Induced dipole. CO2 is nonpolar but when a dipole of water approaches it the electrons of oxygen are repelled by the negative part of water and oxygen is forced to have a dipole.