Chapter 9 and 10

It is possible for two covalently bonded atoms to share more than one electron pair. For example, in a double bond there are _____ shared electron pairs, making a total of _____ shared electrons, and the bond order is _____.

2; 4; 2

Select all the structures in which the polarity of the bond has been marked correctly. Multiple select question. A

A D E

Which of the following statements correctly describe how to draw a Lewis structure? Select all that apply.

A single bond contains two electrons and is represented by a solid line. A Lewis structure includes all the valence electrons in the species. An electron is added to the total count for each negative charge on the species.

A pair of electrons shared between two atoms in a covalent bond is called a shared or______electron pair, whereas an outer-level electron pair that is not involved in bonding is called an unshared or_______pair.

Blank 1: bonding, bonded, or bond Blank 2: lone, nonbonding, non-bonding, nonbonded, or non-bonded

The bond formed between two nonmetal atoms is called a(n)__________bond. This type of bond arises from the net attraction between the____________of each atom and the electrons of the other, and results in electrons being__________between the two atoms.

Blank 1: covalent Blank 2: nucleus or protons Blank 3: shared or localized

Most covalently bonded substances consist of individual separate molecules. Each individual molecule is held together by means of strong__________bonds between the atoms. In addition, there are weak forces of attraction between the individual molecules, called________forces.

Blank 1: covalent, intramolecular, or localized Blank 2: intermolecular, van der Waals, or vanderWaals

In a single, double, or triple bond, the shared electron pairs are localized between the bonded atoms. In a resonance hybrid, electrons are______or spread out over two or more adjacent atoms. Instead of a double or triple bond between two such atoms, the bond is considered a(n)________double or triple bond with a fractional bond order.

Blank 1: delocalized or shared Blank 2: partial

The polarity of a molecule can be expressed in terms of its_________moment (symbol μ), which is the product of the partial____________in the molecule and the__________between their centers.

Blank 1: dipole Blank 2: charges or charge Blank 3: distance, length, or separatio

The bond______is given by the number of electron pairs shared between two bonded atoms. For a double bond such as C=O, this number is______because there is/are________electron pair(s) shared between the two atoms.

Blank 1: order Blank 2: 2 or two Blank 3: 2 or two

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.

Blank 1: polar Blank 2: poles, charges, regions, ends , or charge

Consider the molecule CCl4. Each C-Cl bond in this molecule is____________because the electronegativity difference between C and Cl is_________________than 0.4. Since CCl4 is tetrahedral in shape and symmetrical, the individual bond dipoles___________and the molecule is____________overall.

Blank 1: polar or polar covalent Blank 2: greater, more, larger, higher, or bigger Blank 3: cancel, balance, counterbalance, cancel out, will cancel, or sum to zero Blank 4: nonpolar or non-polar

A molecule that contains covalent bonds and has a(n)__________arrangement of electron groups will have an overall____________polarity, which is measured as a dipole____________

Blank 1: unsymmetrical, non-symmetrical, unbalanced, uneven, asymmetric, unequal, asymmetrical, nonlinear, or imbalanced Blank 2: molecular Blank 3: moment

To draw the Lewis electron-dot symbol for a main-group element, first determine the number of_______electrons by noting the_______number of the element. Place one_____for each electron on each of the four sides of the element symbol, pairing them up once each site has an electron.

Blank 1: valence or outer Blank 2: A group, group, main group, A-group, or main-group Blank 3: dot

The simplest model used to describe the bonding in metals is the electron-sea model. In terms of this model, all the metal atoms contribute their________electrons to form an electron "sea" so that the electrons are________or shared among all the atoms. The metal is held together by the attraction between the metal________and the sea of electrons.

Blank 1: valence or outer Blank 2: delocalized, dispersed, distributed, or pooled Blank 3: cations, ions, nuclei, cores, cation, or ion

A covalent species such as the molecule CH3OH has more than one central atom. Which of the following options correctly describe how to draw a Lewis structure for this species? Select all that apply.

C almost always forms four bonds. C and O could be central atoms because both elements can form more than one covalent bond. Chemical formulas often impart information about atomic arrangements.

Which species has a net dipole moment (i.e., are polar overall)? Select all that apply.

CH2Cl2 NBr3

The nitrite ion, NO2-, is a resonance hybrid and has two resonance forms, as shown. Select all the statements that correctly describe the bonding in this species

Each N-O bond is a partial double bond. The bond order for this species is 1.5. Two electron pairs are delocalized over the entire species.

Which of the following options correctly describe electronegativity?

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

True or false: A molecular covalent substance (such as CO2) has a low melting point because the covalent bonds that hold the molecules together are weak and do not require much energy to break.

False Reason: Correct. Covalent bonds are strong and require a great deal of energy to break. When a molecular covalent substance melts, it is not the covalent bonds that break, but rather the intermolecular forces between the separate molecules. Since these forces are weak, they require much less energy to break.

Which of the following statements correctly describe a covalent bond?

Formation of a covalent bond results in increased electron density between the two nuclei. If the two atoms in a covalent bond approach too closely, the system will become less stable. In a stable covalent bond, nucleus-electron attractions dominate the system.

Which of the following statements correctly describe how to determine whether a given molecule is polar or nonpolar? Select all that appl

If a molecule contains no dipole moments across any bonds, it will be nonpolar. For a molecule that has polar bonds, the geometry must be known in order to predict the overall polarity. If the individual bond dipoles do not cancel, the molecule is polar.

Which of the following statements correctly describe a polar covalent bond?

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.

intermolecular forces

Intermolecular forces are the weak forces of attraction found between the individual molecules of a molecular covalent substance.

Select the correct statements describing molecular covalent solids.

Molecular covalent solids have low melting and boiling points Molecular covalent solids are either soft or hard but brittle. Molecular covalent solids have intermolecular forces between molecules.

Draw the Lewis structure for acetonitrile (CH3CN). Select all the correct statements that apply.

Nitrogen forms a triple bond. The chemical formula gives information about the relative arrangement of the atoms.

Which of the following properties is common to BOTH molecular covalent substances and network covalent substances?

Poor electrical conductivity in any phase

Which of the following options describe how to draw the Lewis electron-dot symbol for a given element?

The Lewis symbol includes only the valence electrons for the element. One dot is placed on each side of the element symbol before pairing any dots. The A-group number of the element gives the number of valence electrons.

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.

Which of the following statements correctly describe the effect of molecular polarity on the behavior of a molecular compound? Select all that apply.

The physical properties of a molecular compound are directly related to molecular polarity. A polar compound will experience stronger intermolecular forces than a nonpolar compound.

Which of the following options correctly explain the differences in physical behavior of molecular covalent substances and network covalent substances?

The strong covalent bonds that hold the atoms of a network covalent substance together require a lot of energy to break. The relatively low boiling points of molecular substances reflect the strength of the intermolecular forces between the individual molecules.

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?

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

A covalent species such as the molecule H3NO has more than one central atom. Which of the following options correctly describe how to draw a Lewis structure for this species? Select all that apply.

There will be three bonds to the N atom. N and O are central atoms because both elements form more than one covalent bond. The O atom will be bonded to both H and N.

Select all the statements that correctly describe the electron-sea model of metallic bonding.

Two or more metals can combine to form alloys of variable composition by sharing their valence electrons. The valence electrons of the bonded atoms are shared in an electron sea.

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 Breaking bonds is always endothermic, and forming bonds is always exothermic.

Resonance structures are Lewis structures that have the same relative placement of _____ but a different arrangement of _____.

atoms; electrons

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.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

network covalent

large molecular structures, strong covalent bonding, share qualities of IONIC AND COVALENT Network covalent substances are extremely hard, whereas molecular covalent substances can be soft or hard.

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+

In general the formation of a chemical bond lowers the _____ energy of a chemical system, leading to a _____ stable arrangement.

potential; more

In general, the formation of a bond between two or more atoms ______.

produces a more stable system lowers the potential energy between oppositely charge particles

Molecular polarity has a direct effect on the behavior of molecular compounds. The attractive forces between polar molecules are _____ than those between nonpolar molecules. It therefore takes _____ energy to separate polar molecules from each other, and a polar compound will have a _____ boiling point than a nonpolar compound of similar size.

stronger; more; higher