chapter 8 bonding and lewis structures

Question 1

Which of the following has both ionic and covalent bonds?
a. KNO2
b. BaO
c. N2O4
d. CsBr
e. HI

Answer 1

a. KNO2

Question 2

Which of the following has both ionic and covalent bonds?
a. H2O
b. NaCl
c. HCl
d. NH4NO3
e. CS2

Answer 2

d.
despite all these elements being non-metals, the bonds between negative and positive polyatomic ions make it both ionic and covalent

Question 3

Which of the following reactions represents the lattice energy of potassium fluoride?
a. KF(s) → K+(g) + F-(g)
b. KF(s) → K(g) + ½F2(g)
c. 2K(g) + F2(g) → 2KF(s)
d. KF(s) → K+(aq) + F-(aq)
e. K+(aq) + F-(aq) → KF(s)

Answer 3

a.
it’s just a 1:1 ratio
lattice energy is the energy required to break a molecule into GASEOUS ions

Question 4

Which of the following is true regarding lattice energy?
a. Compounds with lower magnitude charges and smaller ions have higher lattice energies.
b. Compounds with lower magnitude charges and larger ions have higher lattice energies.
c. Compounds with higher magnitude charges and smaller ions have higher lattice energies
d. Compounds with higher magnitude charges and larger ions have higher lattice energies.
e. None of these

Answer 4

c.

Question 5

Which of the following compounds should have the highest lattice energy?
a. K2O
b. CaF2
c. KI
d. KF
e. CaO

Answer 5

e. CaO
The Ca brings an ion of 2 and the O also does because it’s the absolute value of the charge so it doesn’t matter if it’s negative. So this gives you 4.
The reason it’s not CaF2 is because, despite there being 2 F’s, you only count the charge as 1/2 since there’s 2 of them and the charge of F is -1

Question 6

Which of the following compounds should have the highest lattice energy?
a. NaF
b. Al2O3
c. MgF2
d. Na2O
e. AlF3

Answer 6

b. Al2O3
It has the greatest magnitude with 3 and 2
Just count a single atom of each no matter the subscript

Question 7

Which of the following compounds should have the highest lattice energy?
a. BaS
b. CsBr
c. MgO
d. NaI
e. KI

Answer 7

c. MgO
Both MgO and BaS have the same magnitude so the next deciding factor is which one is smallest? MgO is so it has the highest energy. I guess it’s, the smaller the size of the atoms, the stronger the bonds.

Question 8

Which of the following compounds should have the highest lattice energy?
a. KF
b. KBr
c. KCl
d. CsI
e. KI

Answer 8

a. KF
these all have the same magnitude so the smaller atoms will form the strongest bonds

Question 9

Correctly draw the Lewis dot structure for SiH4. Are there any lone pairs and/or double bonds?

Answer 9

Don’t mistake Si for S
Si is obviously going to be in the middle
Si only has 4 valence electrons and 4 hydrogens = 4 more valence electrons. So it’s just going to have 4 covalent bonds with no lone electrons and no double bonds or lone pairs.

Question 10

Correctly draw the structure for AlH3. Are there any lone pairs and/or double bonds?

Answer 10

This one is going to go under the octet rule since there just aren’t enough electrons to go around. Three covalent bonds. No double bonds or lone pairs. There are just simply 6 valence electrons total.

Question 11

Correctly draw the Lewis structure for N2H4. Are there any lone pairs and/or double bonds?

Answer 11

.. ..
H-N-N-H
I I
H H
Each nitrogen will have a lone pair still. This will make for 14 valence electrons total. The 2 nitrogens wouldn’t have a triple bond between them because this would give each 10 electrons and they have to follow the octet rule and can only have 8

Question 12

Correctly draw the Lewis structure for XeF2? Are there any lone pairs and/or double bonds?

Answer 12

22 total valence electrons. Fluorine can’t exceed the octet rule but Xe can because it’s row 3 or below. So you’re going to have a covalent bond between Xe and each fluorine. And then Xe is also going to have 3 lone pairs. And of course each F will have 6 dots around it.
.. ..
F-Xe-F
..

Question 13

Correctly draw the Lewis dot for PO4^3-

Answer 13

So you’re going to have an extra 3 electrons because of the 3- charge. So that will make 32 total.
One of the oxygens will make a double bond. By doing this, it will take the 1- charge from the oxygen and make it zero. It will also turn the 1 charge on the P and make it zero so that, overall, the molecule will have less formal charges and everything will be closer to zero.

Question 14

Draw the correct Lewis structure for BCL3

Answer 14

This one is a little weird but you have to remember that B can go under the octet rule. So the answer is just 3 covalent bonds, no double bonds.
Plus, without any double bonds, the molecule will have an overall zero charge because there’s a zero formal charge on each atom so that’s good, don’t mess with that.

Question 15

Draw the correct Lewis structure for BrO^-

Answer 15

Basically, there’s 14 valence elctrons. Don’t double bond it because this way it keeps the formal charge on the most electronegative atom (which is one of the optimal rules for formal charges)

Question 16

Draw the correct Lewis structure for IF3

Answer 16

Iodine will have 2 lone pairs to make a total of 28 electrons. The formal charge on each will come out to be zero.
There are no double bonds or anything.

Question 17

Draw the correct Lewis structure for SeF4

Answer 17

There will be 34 electrons total. Se will have a lone pair. There are no double bonds. The formal charge on each (and overall) will be zero.

Question 18

Draw the correct Lewis structure for I3^-

Answer 18

22 electrons total will mean that the central I will have 3 lone pair. The central I will have a negative 1 charge but it’s still better than if you try to do any double bonds. There are no double bonds. Put your drawing in parentheses with a negative sign.

Question 19

Which of the following bonds is the most polar?
a. O-H
b. N-O
c. C-N
d. N-H
e. N-C

Answer 19

a. O-H
The greatest difference in electronegativity determines the polarity. Electronegativity trends opposite atomic radius meaning the greatest electronegativity is up and to the right.

Question 20

Draw the correct Lewis structure for HCN

Answer 20

Carbon will be central because it can make the most bonds. There will only be the single covalent bond between it and hydrogen. N will have one lone pair and a triple bond with carbon. This will give everything a 0 formal charge. Plus, this way, carbon gets a filled octet.

Question 21

Draw the correct Lewis structure for BeCl2

Answer 21

16 total atoms. There will be one covalent bond between each Cl and Be. Be is one that can fall beneath the octet rule so no double bonding is necessary. Plus… without double bonding, the formal charge of everybody is zero.

Question 22

Which of the following compounds has an ionic bond?
a. HCN
b. NH4Cl
c. HCl
d. HF
e. CH3CH2COH

Answer 22

b. NH4Cl

NH4 is a polyatomic ion with a 1+ charge. It fits perfectly with Cl’s 1- charge.
The others are just molecular bonds.

Question 23

Which of the following does not follow the octet rule?
a. CO2
b. CF4
c. XeF4
d. Cl2
e. ICl

Answer 23

c. XeF4

ICl doesn’t violate the rule because there are no extra electrons left over once the covalent bond is made and the lone pairs are added to each atom.

Question 24

In the bisulphate ion (HSO4^-), the formal charge on S is what?
a. -1
b. +2
c. 0
d. +2
e. +4

Answer 24

c. zero

Two of the oxygens will form single covalent bonds. The two other oxygens have double covalent bonds. This makes 6 total bonds on the S atom. And since S has 6 valence electron… 6 - 6 = 0

Question 25

What is the formal charge on the iodine atom in ICl4? hint: this is a polyatomic ion with a 1- charge

Answer 25

negative 1

Question 26

Which of the following is the shortest bond? hint: draw out the Lewis structures a. N2 b. F2 c. Cl2 d. O2 e. they are all the same

Answer 26

a. N2 N2 has a triple bond which is stronger and shorter than any of the others. Cl can be ruled out because it is a much bigger atom

Question 27

Which of the following has the highest bond enthalpy? hint: bond enthalpy is the total amount of energy required to break one mole of a particular molecule a. H-Cl b. H-Br c. H-I d. O-H e. H-F

Answer 27

e. H-F all the choices are single bonds and all involve hydrogen. Therefore, the shortest bond will be the strongest.

Question 28

Given the values for bond enthalpy calculate the enthalpy change (^H) for the reaction between bromine and ethane shown below. C2H6(g) + Br2(g) = C2H5Br(g) + HBr(g) hint: draw out all the bonds, see study guide for the equation C - H 413 C - C 347 Br - Br 193 H - Br 366 C - Br 285 a. -45 kJ/mol b. 92 kJ/mol c. 62 kJ/mol d. 366 kJ/mol e. 81 kJ/mol

Answer 28

a. -45 kJ/mol Basically, you add up all the energies of the reactants and then subtract the total amount of energies of the products.

Question 29

Given that the enthalpy change (^H) for the reaction below is -93 kJ/mol, what is the bond enthalpy of the N-H bond? N2 + 3H2 = 2NH3 (^H) = -93 kJ N triple bond N 945 H - H 436 N - H ? a. 246 kJ/mol b. 391 kJ/mol c. 509 kJ/mol d. 416 kJ/mol e. 360 kJ/mol

Answer 29

b. 391 kJ/mol There's a lot of nuances happening here but, at the end of the day, just set it up like an algebra equation. The energy of the triple N bond is already accounted for meaning, you don't have to multiply the 945 by 3. The H2 bonds, you will multiply by 3 The equation will look like: 945 + 3(436) - x = - 93 But then, you're going to divide that answer by 3 and then by 2 (hence the 2NH3 bond)