SB 9 Pt 2

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+

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

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

A D E

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

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

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

B-Cl C-N H-O

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.

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

Which of the following options correctly describe the general trends in electronegativity? Select all that apply.

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

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.

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).

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

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

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

ionic; polar covalent; nonpolar covalent

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

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

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.