Smartbook Chapter 9 Part 2

The character of a bond is related to the difference in the electronegativities of the bonded atoms. Match each ΔEN range with the appropriate bond type.

ΔEN = 0 --> nonpolar covalent ΔEN < 0.4 --> Mostly covalent ΔEN between 0.4 - 1.7 --> Polar covalent ΔEN > 1.7 --> Ionic

The partial ionic character of a bond is related to the difference in the electronegativities of the bonded elements. The greater the ΔEN, the __________________ the percent ionic character of the bond. Although there are many bonds that have 0% ionic character, no bond has 100% ionic character, which indicates that electron _________________ occurs to some extent in every bond.

higher; sharing

From left to right, Period 3 chlorides exhibit a gradation in bond type from ______ to ______ to ______.

ionic; polar covalent; nonpolar covalent

A polar bond is a covalent bond in which there is an electronegativity difference between the two bonded atoms and electrons are shared unequally. The atom with the higher electronegativity will have a partial _____ charge and is marked with the symbol _____ while the atom with the lower electronegativity will have a partial _____ charge and is marked with the symbol _____.

negative; δ-, positive; δ+

As the ΔEN for a particular bond increases, the character of the bond changes and this is often reflected in the behavior of a substance. The ΔEN for the K-Br bond is 2.0 and ΔEN for the Au-Br bond is 0.4. Match each statement about the K-Br and Au-Br bonds correctly to the descriptions. Instructions

*The K-Br bond is more --> ionic in character*The AU-Br bond is more --> covalent in character*KBr is expected to have --> a relatively high melting point*AuBr2 is expected to have --> a relatively low melting point

The enthalpy of a reaction, ΔHrxn, is the overall heat change resulting from ______ energies when reactant bonds break and ______ energies when product bonds form.

absorbing; releasing

Use the bond enthalpies given to calculate the enthalpy of the reaction: 2H2(g) + O2(g) → 2H2O(g) H-H = 436.4 kJ/mol; H-O = 460 kJ/mol; O=O = 498.7 kJ/mol

-468.5 kJ/mol

Which option correctly describes the influence of electronegativity difference (ΔEN) on bond character? Select all that apply.

A bond with ΔEN of 0.4 or less is considered mostly covalent. A bond with ΔEN greater than 1.7 is considered to be mostly ionic.

Select all the structures in which the polarity of the bond has been marked correctly.

A, D, E A: Carbon d+, O d- D: HN towards N E: O d+ F d-

The bonding of chlorine with each of the Period 3 elements shows a change in bonding type from ionic through polar covalent to nonpolar covalent. Select the properties that reflect this change in bonding character.

Electrical conductivity at the melting point is high only for chlorides of Group 1A(1) and Group 2A(2). Electron density relief maps show a steady increase in electron sharing from NaCl to Cl2. There is a general decrease in ΔEN moving from left to right across the period.

Which of the following options correctly describe electronegativity? Select all that apply. The most electronegative element is hydrogen because it has the smallest atomic size. Electronegativity is a relative quantity. Electronegativity is another word for electron affinity. Electronegativity can be measured by measuring the energy changes when an atom gains an electron. Electronegativity measures the ability of an atom in a covalent bond to attract the shared electron pair(s).

Electronegativity is a relative quantity. Electronegativity measures the ability of an atom in a covalent bond to attract the shared electron pair(s).

Which of the following options correctly describe the general trends in electronegativity? Select all that apply. Electronegativity tends to increase as atomic size increases. Electronegativity tends to decrease from left to right across a period of the periodic table. Fluorine is the most electronegative element. Electronegativity tends to decrease down a group of the periodic table. Metals tend to have lower electronegativities than nonmetals.

Fluorine is the most electronegative element. Electronegativity tends to decrease down a group of the periodic table. Metals tend to have lower electronegativities than nonmetals.

Using the table of electronegativity values provided, which of the following bonds are polar covalent? Select all that apply.

H-O C-N B-Cl

Which of the following statements correctly describe a polar covalent bond? Select all that apply.

In a polar covalent bond the electron density is highest over the more electronegative atom. A bond between atoms whose electronegativities differ by more than 0.4 but less than 1.7 is polar.

Using the table of electronegativities provided arrange the following bonds in order of increasing ionic character. (Place the least polar bond at the top of the list.)

Pd-H C-H N-O F-Cl

Select the statement that correctly explains the source of the energy change in a chemical reaction.

The main contribution to ΔH is the difference in the bond energies of reactants and products.

Select the statement that correctly summarizes the steps to calculate ΔHo of a reaction using bond enthalpies.

The sum of the bonds formed (exothermic) in the reaction is subtracted from the sum of the bonds broken (endothermic).

Which of the following options correctly describe the procedure used to calculate ΔH for a reaction using bond energies? Select all that apply.

The sum ΔHbonds broken is given a positive value. ΔH for the reaction is given by (sum of ΔHbonds broken) + (sum of ΔHbonds formed)

In general, electronegativity _____ as atomic size increases because a shared electron pair is closer to the nucleus of a smaller atom, which therefore attracts these electrons _____ strongly. Electronegativity tends to _____ from left to right across a period of the periodic table and tends to _____ down a group.

decreases; more; increase; decrease

The relative ability of a bonded atom to attract shared electron pairs is called its _____. This ability _____ as the size of the atom decreases because for a smaller atom the shared electrons will be closer to the nucleus.

electronegativity; increases

The percent ionic character of a bond ______ with ΔEN. An arbitrary value of ______ divides ionic from covalent bonding.

increases; 50% ionic character

The greater the ΔEN between bonded atoms, the ______ the partial charges on the atoms and the ______ the partial ionic character of the bond.

larger; higher

A covalent bond in which the electrons are shared unequally is called a(n) _________________ covalent bond. The atoms of the bond have partial negative and positive __________________ due to unequal electron distribution.

polar; charges

Consider the reaction shown. Select all the statements that correctly apply to the calculation of ΔH for this reaction using the bond energies provided.

ΔH for this reaction is equal to -168 kJ/mol. In this reaction, two C-Cl bonds are formed.