Chapter 9

Question 1

what is a chemical bond

Answer 1

a strong attractive force that exists between neighboring atoms in a substance

Question 2

three types of chemical bonds

Answer 2

• ionic
• covalent
• metallic

Question 3

what is a metallic bond

Answer 3

a regular arrangement of metal atoms, but the valence electrons move throughout the crystal

Question 4

what is an ionic bond

Answer 4

a chemical bond formed by the electrostatic attraction between positive and negative ions

Question 5

when do ionic bonds form

Answer 5

when one or more electrons are transferred from the valence shell of one atom to the valence shell of another atom

Question 6

the atom that transfers electrons in ionic bonds

Answer 6

cation

Question 7

the atom that gains electrons in an ionic bond

Answer 7

anion

Question 8

G.N Lewis

Answer 8

introduced the Lewis Electron-Dot symbol to describe ions and molecules by considering a “cubical atom”

Question 9

G.N Lewis and his hypothetical “cubical atom”

Answer 9

there is space for 8 electrons at the corners of a hypothetical cube

Question 10

what did G.N Lewis recognize about atoms

Answer 10

there is a “kernel” of electrons that remain uncharged, and an outer shell that varies during chemical reactions between 0 and 8

Question 11

valence electrons

Answer 11

the outer shell electrons of an atom. they are the electrons that participate in chemical bonding

Question 12

Lewis’s Cubical Atom (definition)

Answer 12

a cube provides a simple means to illustrate valence electrons around an atom, but this is more commonly represented in 2-dimensions using “dots” to represent the valence electrons

Question 13

Lewis dot symbol

Answer 13

a notion in which the electrons in the valence shell of an atom or ion are represented by dots placed around the chemical symbol of the element

Question 14

how are lewis dot symbols placed

Answer 14

dots are placed one to a side until all 4 sides are occupied

Question 15

what concept did Lewis introduce

Answer 15

the electron-pair bond and the “group of 8” electrons being the favorable situation

Question 16

what did Lewis’s concept lead to

Answer 16

-the octet rule

Question 17

octet rule definition

Answer 17

-molecules or ions tend to be most stable when the outermost electron shells contain 8 electrons and have structures that are isoelectronic with the noble gasses

Question 18

what does the combination of ionization energy and electron affinity need

Answer 18

it needs energy because it is endothermic

Question 19

lattice energy

Answer 19

the change in energy when an ionic solid is separated into gas-phase ions

Question 20

what happens when 2 ions bond

Answer 20

energy is released, making the overall process exothermic

Question 21

according to Coulombs law, what 2 factors affect the strength of the ionic bond

Answer 21

• charge (Q)

- size of the ions

Question 22

Coulomb’s Law

Answer 22

the energy (E) obtained in bringing 2 ions with electric charges Q+ and Q- from infinite separation to a distance (r) apart

Question 23

equation for coulomb’s law

Answer 23

E=(Q+ x Q-)/r

Question 24

Q+

Answer 24

the charge on the cation

Question 25

Q-

Answer 25

the charge on the anion

Question 26

r

Answer 26

the distance between the ions

Question 27

what does solving for E in coulomb's law give you

Answer 27

the strength of the ionic bond

Question 28

ionic substances are typically ________ solids

Answer 28

high-melting

Question 29

what 2 factors affect the strength of the ionic bond (Melting point: Coulomb's Law

Answer 29

melting point (strength of ionic bond) increases as Q increases and/or as r decreases

Question 30

covalent bond

Answer 30

a chemical bond formed by sharing a pair of electrons

Question 31

how do we understand how covalent bonds form

Answer 31

- we monitor the energy of two isolated hydrogen atoms as they move closer together - the energy decreases, first gradually and then more steeply, to a minimum - as the atoms continue to move closer, energy starts to increase dramatically because the nuclei repel

Question 32

bond length

Answer 32

the distance between the atoms when energy is at a minimum

Question 33

what is the importance of the Born-Haber Cycle

Answer 33

because it is very difficult to measure the lattice energy directly, using the energy changes for steps helps make it easier and gives the same result

Question 34

Orbitals

Answer 34

a place to put electrons

Question 35

Elements to the left of carbon have __________ and those to the right have ________

Answer 35

empty orbitals filled orbitals (lone pairs)

Question 36

coordinate covalent bond

Answer 36

is one where a single atom provides | both electrons

Question 37

Bond Lengths sorted by size

Answer 37

Triple bond < Double Bond < Single Bond

Question 38

Ionization energy and electron affinity provide

Answer 38

an indication of how readily an atom may want to give up or accept an electron

Question 39

Electronegativity is considered to be

Answer 39

the ability of an atom | in a molecule to attract electrons to itself.

Question 40

Linus Pauling

Answer 40

quantified the concept of electronegativity by comparing the bond energy of a heteronuclear A-B bond with the corresponding homonuclear A-A and B-B bond energies.

Question 41

The bond energy E(A-B) for a molecule A-B is always

Answer 41

greater than | the mean of the bond energies

Question 42

Pauling argued that the excess bond energy is due to the

Answer 42

ionic | component caused by the partial charges on the atoms in AB.

Question 43

Electron Affinity versus Electronegativity

Answer 43

Electron Affinity: measurable, Cl is highest. Electronegativity is the ability of an atom to attract toward itself the electrons in a chemical bond. Electronegativity: relative, F is highest

Question 44

when the difference in electronegativity is 0

Answer 44

the bond is covalent

Question 45

when the difference in electroegativity is greater than or equal to 2

Answer 45

the bond is ionic

Question 46

when the difference in electronegativity is between 0 and 2

Answer 46

the bond is polar covalent

Question 47

Formal charge results from assuming

Answer 47

equal sharing of the | bonding electrons

Question 48

The formal charge on an atom in a Lewis dot structure is | determined by inspecting

Answer 48

how many lone pairs are present and | how many bonds it forms.

Question 49

The sum of the formal charges of the atoms in a molecule or ion must equal

Answer 49

the charge on the molecule or ion.

Question 50

Resonance

Answer 50

means that the actual structure is a composite or an | average of the two structures.

Question 51

classic example of "resonance".

Answer 51

benzene

Question 52

A "circle" is used to depict the fact that

Answer 52

the bonding cannot be properly represented by a single Lewis structure in which a "line" represents a shared electron pair bond

Question 53

Exceptions to the Octet Rule

Answer 53

1. The incomplete octet (hypovalent or electron deficient molecules). 2. Odd-electron molecules 3. Hypervalent molecules ("valence shell expansion")

Question 54

Bond order

Answer 54

is the number of pairs of electrons in a bond.

Question 55

bond energy

Answer 55

The enthalpy change required to break a particular bond into one mole of gaseous molecules

Question 56

Bond energy is a measure of

Answer 56

bond strength: the greater the bond energy, | the stronger the bond, the more stable the molecule

Question 57

Bond energies can be used to estimate the

Answer 57

enthalpy change, ΔH, for a | reaction