Chapter 8 Practice

1 D =

3.34×10−30 C⋅m1

What is the bond dissociation energy for breaking all the bonds in a mole of O2 molecules?

498 kJ/mol O=O = +498

Calculate the bond dissociation energy required for breaking all the bonds in a mole of water molecules, H2O.

920 kJ/mol H-O = +460 x 2

Calculate the bond dissociation energy needed to break all the bonds in a mole of carbon dioxide, CO2.

1464 kJmol C=O = +732 x 2

What type of bonding occurs in a sample of pure cobalt, Co? In other words, how is one cobalt atom held to another cobalt atom?

metallic two metals lose electrons and form a sea of electrons that cations are attracted to, forming a metallic bond

dipole moment

μ=Q×r

Calculate the approximate enthalpy change ,ΔH∘, for the combustion of methane: CH4+2O2⇌2H2O+CO2

-688kJ -Since you are multiplying energy by the number of each moles of each bond that breaks/forms, the denominator cancels out -ΔH∘ = D(reactants)-D(products)

How many lone pairs are on the central atom in BCl3?

0 -Boron has 3 valence electrons and must bond to 3 chlorine atoms, so there are no electrons left to form lone pairs. -Elements in the second period left of Nitrogen are exceptions to the octet rule (< 8 electrons)

The Lewis structure for the chlorate ion is... Calculate the formal charge on the chlorine (Cl) atom.

0 7-2-0.5(10)=0

What are the formal charges on the sulfur (S), carbon (C), and nitrogen (N) atoms, respectively, in the resonance structure that contributes most to the stability of the thiocyanate ion, SCN−? The possible resonance structures for the thiocyanate ion, SCN−, are...

0, 0, -1 In the dominant Lewis structure, (1) the atoms have formal charges closest to 0 (2) the negative formal charge is on the most electronegative atom

Calculate the formal charge on each of the oxygen (O) atoms labeled a, b, and c in the following Lewis structure.

0, 0, -1 6-4-0.5(4)=0 6-4-0.5(4)=0 6-6-0.5(2)=-1

How many electrons should be shown in the Lewis symbol for hydrogen

1 H has one valence electron and can only form one bond (duet)

The dipole moment (μμmu) of HBr (a polar covalent molecule) is 0.844D (debye), and its percent ionic character is 12.5 %% . Estimate the bond length of the H−Br bond in picometers.

1.4x10^-10m or 140pm (0.844D*3.34x10^-30C*m)/0.125(1.6x10^-19C)

n a bond with 100%% ionic character, Q=

1.6×10−19 CQ=1.6×10−19 C.

Calculate the bond dissociation energy for the breaking of all the bonds in a mole of methane, CH4.

1640 kJ/mol C-H = +410 x 4

How many lone pairs are on the central atom of BrF3?

2 -Bromine has 7 valence electrons and forms 3 bonds with Florine, leaving 4 electrons to form lone pairs -Elements in periods 3-6 can use d-orbitals (hold 10 electrons as opposed to 8), making it an exception to the octet rule

How many resonance structures can be drawn for ozone, O3?

2 The two structures are equivalent and the actual structure is an average of both the resonance structures.

Given the following thermodynamic data, calculate the lattice energy of CaBr2(s). ΔHf∘[CaBr2(s)] -675 ΔHf∘[Ca(g)] 179 ΔHvap[Br2(l)] 30.8 ΔHbond[Br2(g)] 193 I1(Ca) 590. I2(Ca) 1145 E(Br) -325

2163 kJ/mol sum the enthalpy values of the steps but be mindful of modifications -change the sign of ΔHf∘[CaBr2(s)] (direction of arrow) -double the value of E(Br) (due to stoichiometry)

Rank the following ionic compounds by lattice energy: MgO, LiCl, Na2S, BeO, Na2O

BeO, MgO, Na2O, Na2S, LiCl Mg (2+) O (2-) Be (2+) O (2-) Mg > Be Na2 (1+) S (2-) Na2 (1+) O (2-) S > O *Lattice energy inversely proportional to distance between center of ions Li (1+) Cl (1-) rank the cation and anion charges to find the magnitude of charge. compare the relative radii of ions in a compound when ionic charges are the same

Select the best Lewis structure for HCH2Br

C central atom (octet), Br right (octet), H top left and bottom (duet) -C will form 4 bonds while H and Br can only form 1 bond -The least electronegative atom will be the central atom.

Arrange the following elements in order of decreasing electronegativity: Cobalt, sulfur, potassium, chlorine

Chlorine > Sulfur > Cobalt > Potassium Electronegativity increases across a period (left-right) and up a group

Which statement best describes an O3 molecule?

Each atom in ozone is connected to another atom by a bond having a bond order of 1.5.

Use the following table to rank these bonds in order of decreasing bond length. I-F 273 I-I 148 I-Cl 208 I-Br 175

I-I > I-Br > I-Cl > I-F

Classify each element as a metal, nonmetal, or semimetal: He, Mg, In, Co, Si, S

Metals: Mg, In, Co Nonmetals: He, S Semimetal: Si Metals generally have low electronegative values

Which of these molecules has a Lewis structure with a central atom having no nonbonding electron pairs? -SiF4 -H2S -PF3 -CO2

SiF4, CO2 Draw Lewis Structure; both CO2 and SiF4 have central atoms with no nonbonding electrons

The hydrogen atom is not actually electronegative enough to form bonds to xenon. Were the xenon-hydrogen bond to exist, what would be the structure of XeH4?

Xe has 4 single bonds to 4 H atoms. Xe has 2 lone pairs. -Xe is an exception to the octet rule and can have more than 8 valence electrons (formal charge = 8-4-0.5(8)=0) -H forms duets

Phosphorus pentoxide (P4O10) is used as a dehydrating agent in many organic synthesis reactions. What type of bonding occurs between the atoms of a P4O10 molecule?

covalent two nonmetals share electrons to form a covalent bond

What type of bonding occurs in zinc(II) chloride, ZnCl2?

ionic an anion and a cation form an ionic bond