Describe the type of bonding in sodium metal and explain why sodium is a good conductor of electricity
Metals are held together by the attraction of the positive ions for the sea of electrons
Because electrons are not localized (attached to a specific atom) they can move around relatively easily. This makes metals highly conductive
Name and describe the bonding within and between the molecules in liquid fluorine
Flourine atom bond covalently to make the F2 molecule. The molecule is non-polar because the electrons are shared evenly between the two atoms. The intermolecular forces experienced by liquid fluorine are dispersion forces which are weak forces due to temporary induced dipole.
Write the electron structures of both sodium and fluorine and describe how the atoms combine to form sodium fluoride
It is a dipole that forms because of random fluctuations of electrons in a molecule. If a bunch of electrons move to one side of a molecule, they induce a dipole on an atom nearby since it’s electrons will move away from the other molecule creating oppositely charged poles
Identify the strongest type of intermolecular force in the following:
CH4 Dispersion forces
CH3OH Hydrogen bonding
Rank the strength of the following compounds from strongest to weakest intermolecular forces. PCl3, NiCl2, I2, HF
I2 has dispersion forces since it is non-polar
NiCl2 will have ion-ion forces since it is most likely an ionic bond (presence of metal makes an ionic bond)
PCl3 (P-Cl bond has electronegativity difference of 0.9 and molecule is not symmetrical due to lone pair on P)
HF (H-F bond has electronegativity difference of 1.9) so it’s more polar than P-Cl and has the ability to hydrogen bond.
NiCl2 > HF > PCl3 > I2
Which of the above 4 compounds are likely to dissolve in water?
NiCl2, HF and possibly PCl3 since ionic and polar compounds are able to dissolve in water
Which of the above 4 compounds are likely to dissolve in a non-polar solvent?
In ethanol, C2H5OH(l),there are covalent bonds, hydrogen bonds and van der Waals. forces. Which bonds or forces are broken when ethanol is vaporized?
Van der Waals forces and hydrogen bonds are broken when ethanol evaporates. When a substance evaporates it changes from a liquid to a gas but it does not change chemical composition so only intermolecular forces are broken – not covalent bonds.
True or false: Elements that covalently bond have very low electronegativity values
False. Just because the elements have low electronegativity values doesn’t mean they will covalently bond. The difference in electronegativity is what matters. For example, Fluorine has a very high electronegativity and makes covalent bonds when it bonds with itself. Sodium which has a very low electronegativity makes ionic or metallic bonds – not covalent bonds.
Cu and Hg are both metals and therefore bond via metallic bonding which is a bunch of cations held together by an electron sea. Because the electrons are delocalized, the electrons can move easily and therefore, conduct. Hg’s conductivity is slightly lower than that of Cu because it doesn’t like to share electrons (which is why it’s a liquid at room temperature- doesn’t have the strong metallic bonds formed through delocalization). LiOH (aq) also has relatively high conductivity since ionic compounds separate into ions when they are dissolved in water. The presence of ions in water makes the water a good charge carrier. H2 is a terrible conductor because electrons are very localized between the hydrogen atoms.
State and explain the relative solubility in water of the following substances
CH3CH3 not soluble – non-polar
CH3OCH3 not very soluble – has some ability to make dipole-dipole forces
CH3CH2OH pretty soluble because of ability to hydrogen bond
CH3CH2CH2CH2OH not soluble because of large non-polar carbon chain
State and explain the relative boiling points for the following substances
Note that the following substances have about the same mass (about 60 amu)
CH3CH2CH2OH capable of hydrogen bonding so has highest boiling point
CH3OCH2CH3 primary intermolecular force is dipole dipole which is weaker than H-bonds for molecules of same mass. So b.p is between that of substances of a and b.
Why is important that the molecules in the previous question have the same mass?
Because than you can compare intermolecular forces more easily. Molecules of lower mass may have lower boiling points because they are lighter and therefore need less energy to evaporate even though the forces between the molecules might be stronger than another molecule with a large mass.
Which molecule has the most ionic character
CO2 isn’t even a contender since two non-metals make a covalent bond.
Hydrogen often forms covalent bonds with non-metals. It has a much higher electronegativity than other alkali metals and alkaline earth metals. So CaO or MgS must have the most ionic character. Remember that the most ionic character is determined by the difference in electronegativity so we need to identify the pair that have the greatest difference. The trend is that electroengativity increase across the periodic table and decreases down the periodic table. So Oxygen is more electronegative than Sulfur and Magnesium is more electronegative than Calcium so CaO will have a bigger difference and therefore the most ionic character.
Which molecule has the greatest polarity?
Fluorine obviously non-polar since difference in electroneg. is zero.
Hydrogen fluoride most polarity (largest difference in Electronegativity and is not symmetrical)
Hydrogen chloride less polar than HF since Cl has lower electronegativity than F because of shielding of outer electrons
Tetrafluoromethane (CF4) non-polar molecule because it’s symmetrical.
When hydrogen bonds with sulfur it makes a gas, when it bonds with oxygen, it makes a liquid. If sulfur and oxygen are in the same family, why are the properties of H2S and H2O so different?
Oxygen is much more electronegative than sulfur and therefore makes more polar bonds with hydrogen than sulfur does. The polar bonds cause strong intermolecular forces – hydrogen bonding that make water a liquid at room temp rather than a gas. Sulfur is less electronegative because it has one more energy level filled. The eight inner electrons of Sulfur’s second energy level shield the outer electrons a lot Problem Set 11.1 Answers
Determine which ion will form
Explain why the ion formation by a transition metal cannot be predicted
Transition metals have more than one possible oxidation state
Give the kind of bonding in the following comounds
Ionic (between Na and SO42-) and covalent (between S and O)
Ionic because between metal and non-metal. Some may classify as polar covalent (metals with high oxidation states form polar bonds when bonding with non-metals)
Non-polar covalent (two non-metals with similar electronegativities)
polar covalent (bond is polar b/c two non-metals with different electronegativities but molecule is non-polar)
polar covalent (however, molecule is non-polar)
polar covalent (however, molecule is non-polar)
valence of 6 gives charge of -2 and valence of 2 gets a charge of +2 so formula is Y2+X2-
4 valence electrons (needs 4 bonds or two double bonds) and 6 valence electrons (needs two bonds or one double bond) so must be QR2.
Boron can break the octet rule – it can have only 6 electrons around it
Elements in the third row of the periodic table can also break the octet rule
SiH4 = tetrahedral and PH3 = trigonal pyramidal. The bond angles are different even though they are both based on the tetrahedral electron arrangement because the PH3 molecule has a lone pair that repels bonding pairs more.
Principles of VSEPR
Valence electron pairs repel each other – lone pairs repel more than bonding pairs