Chapter 9

Question 1

what is the lewis theory?

Answer 1

a simple model of chemical bonding using diagrams that represent bonds between atoms as lines or pairs of dots. In this theory, atoms bond together to obtain stable octets

Question 2

what is metallic bonding?

Answer 2

the type of bonding that occurs in metal crystals, in which metal atoms donate their electrons to an electron sea, delocalized over the entire crystal lattice

Question 3

what is a chemical bond?

Answer 3

the sharing or transfer of electrons to attain stable electron configuration

Question 4

what is the octet rule?

Answer 4

The tendency for most bonded atoms to possess or share eight electrons in their outer shel to obtain stable electron configurations and lower their potential energy

Question 5

what is lattice energy?

Answer 5

the energy associated with forming a crystalline lattice from gaseous ions

Question 6

what is the Born-Haber cycle?

Answer 6

A hypothetical series of steps based on Hess’s law that represents the formation of an ionic compound from its constituent elements

Question 7

What are the steps in the Born-Haber cycle (example NaCl)?

Answer 7

1. formation of gaseous sodium from solid sodium
2. Formation of chlorine atoms from chlorine molecule
3. ionization of sodium gas
4. addition of electron to gaseous chlorine
5. formation of crystalline solid from gaseous ions

Question 8

Summarize the trends in lattice energies?

Answer 8

1. lattice energies become less exothermic (less negative) with increasing ionic radii
2. lattice energies become more exothermic (more negative) with increasing magnitude of ionic charge

Question 9

what are bonding pairs?

Answer 9

a pair of electrons shared between two atoms

Question 10

what are lone pairs (non-bonding electrons) ?

Answer 10

a pair of electrons associated with only one atom

Question 11

what is a double bond?

Answer 11

the bond that forms when two pairs of electrons are shared between two atoms

Question 12

what is a triple bond?

Answer 12

The bond that forms when three electron pairs are shared between two atoms

Question 13

summarize the method for drawing lewis structures as follows

Answer 13

1. Calculate the total number number of electrons for the Lewis structure by summing the valence electrons of each atom in the molecule
2. write the correct skeletal structure for the molecule drawing a bond between each set of bonding atoms
3. distribute the remaining unaccounted-for electrons, in pairs, among the atoms, giving octets (except for hydrogen) to as many atoms as possible
4. If any non-hydrogen atoms lack an octet, form double, or triple bonds as necessary to give them octets

Question 14

what does bond energy mean?

Answer 14

the energy required to break 1 mol of the bond in the gas phase

Question 15

what is an exothermic reaction?

Answer 15

a reaction is exothermic when weak bonds break and strong bonds form ie) energy is released

Question 16

what is an endothermic reaction?

Answer 16

a reaction is endothermic when strong bonds break and weak bonds form ie) energy is absorbed

Question 17

what is bond length?

Answer 17

the average length of a bond between two particular atoms in a variety of compounds

Question 18

bond lengths are what?

Answer 18

bond lengths are not static, the distance between two atoms is not the same all the time, the two atoms move towards and away from each other constantly by a spring

Question 19

what is bond-stretching vibration?

Answer 19

the molecular motion of bonds stretching and contracting

for a bond vibration to take place, energy must be supplied to the molecule

Question 20

what is Infrared Spectroscopy?

Answer 20

The absorption of Infrared radiation by a compound can be measured easily by irradiating the sample with an infrared source called a (glow bar) and measuring the intensity of radiation transmitted through the sample at each wavelength or frequency

Question 21

what is a wavenumber?

Answer 21

the reciprocal of wavelength

Question 22

what is a polar covalent bond?

Answer 22

A covalent bond between two atoms with significantly different electronegativities, resulting in an uneven distribution of electron density

Question 23

what does electronegativity mean?

Answer 23

the ability of an atom to attract electrons to itself in a covalent bond

Question 24

what are the periodic trends in electronegativity?

Answer 24

1. electronegativity GENERALLY INCREASES across a period in the periodic table
2. electronegativity GENERALLY DECREASES down a column in the periodic table
3. Fluorine is the most electronegative element
4. Francium is the least electronegative element (most electropositive)

Question 25

The effect of electronegativity difference in bond type?

Answer 25

1. EN = 0-0.4; covalent (non-polar); Cl2
2. EN = 0.4-2.0; Polar covalent (slightly polar); HCl
3. EN = 2.0+; Ionic (polar); NaCl

Question 26

what is a dipole moment (u)?

Answer 26

a measure of the separation of positive and negative charge in a molecule

Question 27

what is percent ionic character?

Answer 27

The ratio of a bond’s actual dipole moment, it would have if the electron were transferred completely from one atom to another and then multiplied by 100%

Percent Ionic Character = measured dipole moment of bond / dipole moment if electron were completely transferred * 100%

Question 28

what are resonance structures?

Answer 28

two or more valid Lewis structures that are shown with double-headed arrows between them to indicate that the actual structure of the molecule is intermediate between them

Question 29

what is a resonance hybrid?

Answer 29

The actual structure of a molecule that is intermediate between two or more resonance structures

Question 30

what is formal charge?

Answer 30

The charge that an atom in a lewis structure would have if all the bonding electrons were shared equally between the bonded atoms

Formal charge = #of valence electrons - (#of bonding electrons + 0.5 #of bonding electrons)

Question 31

the sum of formal charge must?

Answer 31

The sum of formal charge must equal the overall charge of the ion or molecule

Question 32

what are the two guidelines to follow when drawing a lewis structure of a molecule?

Answer 32

1. smaller formal charges on individual atoms are better that larger ones
2. when formal charges cannot be avoided, negative formal charges reside on the most electronegative ion

Question 33

what are free radicals?

Answer 33

a molecule or ion with an odd number of electrons in its lewis structure (not an octet, more than 8)