Chapter 2: Chemical Bonding and Lewis Structures

Question 1

compounds (2)

Answer 1

• chemicals that are combinations of 2 or more different elements in defined properties
• do not have overall charges (“charge neutral”)

Question 2

ions (2)

Answer 2

• species possessing an overall negative charge or overall positive charge
• cannot be isolated, (they are insoluble) in their condensed phases (liquid, solid) without ion of opposite charge present to balance the charge to form a net-neutral compound

Question 3

anion

Answer 3

• ions carrying an overall negative charge

Question 4

cation

Answer 4

• ions carrying an overall positive charge

Question 5

simple ions

Answer 5

• ions that contain a single atom

Question 6

complex ions (2)

Answer 6

• ions that contain multiple atoms

- aka polyatomic atoms or molecular atoms

Question 7

purpose of forming bonds

Answer 7

• elements achieve a lower overall energy than they would in their free elemental form

Question 8

ionic bonds

Answer 8

• occur when oppositely charged ions are help together by electrostatic forces

Question 9

covalent bonds

Answer 9

• occur when atoms are held together by mutual attraction of a pair (or pairs) of electrons to the nuclei in adjacent atoms, the electrons are “shared” between atoms

Question 10

metallic bonds (2)

Answer 10

• occur when electrons are shared between many atoms simultaneously and are free to “flow” between atoms
• in elemental metals or metallic alloys (mixture of two or more elemental metals), this bond is the most important

Question 11

electronegativity (2)

Answer 11

• tendency of an atom in a molecule to attract electrons to itself
• cannot be discussed unless it is apart of a molecule or molecular ion

Question 12

polar covalent bonds

Answer 12

• electrons are polarized towards the atom with greater electronegativity, so the electrons are shared unequally

Question 13

bond polarity (2)

Answer 13

• measured by the subtraction of the lesser electronegativity from the greater electronegativity
• bonds with high differences in electronegativity can be considered to be ionic

Question 14

ionic compounds (4)

Answer 14

• commonly referred to as salts
• consist of ions held together with electrostatic forces
• when melted, cations and anions move past each other freely and resulting liquid conducts electricity
• can carry a charge from one place to another, motion of charged ions result in an electric current

Question 15

can covalent compounds conduct electricity in a liquid state?

Answer 15

• they do not conduct electricity as there are no ions present after melting, covalent bonds remain intact during phase changes

Question 16

how do the alkali metals (group 1) and alkaline earth metals react (group 2) in ionic compounds

Answer 16

• group 1 metals are found as M+ ions in ionic compounds

- group 2 metals are found as M2+ ions in ionic compounds

Question 17

redox reaction (2)

Answer 17

• total number of electrons lost must be equal to the total number of electrons gained
• in a reaction between an alkali metal atom and a halogen atom the electron is formally transferred from the alkali to the halogen: the alkali metal is oxidized and the halogen is reduced

Question 18

covalent bond (2)

Answer 18

• exists when a pair of electrons is shared between 2 atoms

- pair of electrons is called a bond pair, valence electrons that do not participate are called lone pair

Question 19

bond order

Answer 19

• number of bond pairs between two atoms

Question 20

bond length

Answer 20

• distance between 2 nuclei participating in a bond

Question 21

bond dissociation energy

Answer 21

• determines strength of a bond, experimental value describing how much energy needs to be added to break a particular bond

Question 22

describe the trend between bond order, length and dissociation energy

Answer 22

• smaller bond order: larger bond length and smaller dissociation energy

Question 23

bond dipole (2)

Answer 23

• result of electrons being polarized towards the atom with greater electronegativity
• one atom will have a partial positive charge and the other will have a partial negative charge

Question 24

what symbol is used to indicate a bond dipole

Answer 24

• arrow with a crossed tail is used to indicate the direction of a bond dipole (points towards excess negative charge)

Question 25

how do you measure percent character of a bond

Answer 25

• ratio of the actual bond dipole to the bond dipole if the bond was purely ionic

Question 26

octet rule

Answer 26

• atom satisfy this rule is they have 8 valence electrons, achieved by forming covalent bonds

Question 27

how do you determine whether an atom has a complete octet?

Answer 27

1. count the lone pair electrons on the atom
2. count all bonding electrons (twice the number of bonds to the atom)
3. octet rule is satisfied if #1 and #2 have a complete octet

Question 28

“electron deficient” compounds (2)

Answer 28

• group 13 elements only have 3 valence electrons in their outer shell and can achieve a maximum of six valence electrons
• these compounds do not have to conform to octet rule as they are unable to achieve a complete octet

Question 29

hypervalent species (3)

Answer 29

• species containing elements in the third or later periods of the p-block may have more than an octet of electrons
• central atom has an expanded octet
• “central atom with more electrons in its valence shell then predicted in the octet rule”

Question 30

free radicals

Answer 30

• species that contain unpaired electrons

Question 31

formal charge

Answer 31

• determined by imagining bonding electrons are shared exactly equally between atoms and occurs when bonded atom has a greater or fewer number of electrons than its free form

Question 32

what is the procedure for drawing valid lewis structures for species with one central atom

Answer 32

1. arrange atom symbols
2. add valence electrons
3. draw bonds
4. rearrange electrons for octet and check octet rule
5. label formal charges
6. check electron count

Question 33

when do resonance structures exist? (2)

Answer 33

• when two are more Lewis structures can represent the arrangement of electrons in the same molecule or molecular ion
• positions and connectivity of the atomic nuclei are identical

Question 34

valid resonance structures

Answer 34

• any structure where the octet rule is satisfied on all atoms (other than known exceptions)

Question 35

best resonance structures

Answer 35

• a structure that has minimal formal charges and has negative formal charges on more electronegative elements

Question 36

chemically reasonable resonance structure (2)

Answer 36

• any valid resonance structure where the magnitudes of the formal charges are small
• represent bonding that is typical of various elements

Question 37

isomers

Answer 37

• chemical species that have the same molecular formula, but a different arrangement of atoms, not to be confused with resonance structures

Question 38

acid-base theory

Answer 38

• the acid is the proton (H+) donor and the base is the proton acceptor