Chapter 9

Question 1

why do chemical bonds form

Answer 1

they lower potential energy between charged particles that compose atoms

Question 2

ionic bond

Answer 2

metal + nonmetal bond and the metal transfer 1 or more electrons to nonmetal

Question 3

covalent bond

Answer 3

nonmetal + nonmetal; electrons are shared, not transferred

Question 4

metallic bonding

Answer 4

metal + metal; simplest form is electron sea model where atoms in metal lattice pool their valence electrons and are delocalized over the entire metal

Question 5

lattice energy

Answer 5

energy associated with formation of crystalline lattice; always exothermic so lattice energy is always negative
ionic radii increase as we move down the column

Question 6

ionic bond properties

Answer 6

ionic solids:
high melting points
nonconductive
solutions of ionic compounds conduct electricity

Question 7

bond length and strength

Answer 7

double bond is shorter and stronger than single

triple bond is shorter and stronger than double

Question 8

difference in direction and melting point for covalent vs ionic

Answer 8

covalent = shares a specific pair of electrons
ionic = non directional and share an array of ions
molecular compounds have lower melting and boiling points than ionic compounds

Question 9

electronegativity

Answer 9

atom’s ability to attract electrons in a chemical bond

Question 10

periodic trends for electronegativity

Answer 10

increases across period
decreases down a column
flourine = most electronegative
Francium = lease electronegative

Question 11

degree of polarity depends on..

Answer 11

difference between electronegativity of two bonding atoms

greater difference = more polar

Question 12

dipole moment

Answer 12

measure of the separation of positive and negative charge

Question 13

percent ionic character

Answer 13

increases with electronegativity difference
no bond is 100% ionic
ratio of bond’s actual dipole moment to dipole moment it would have if electron was completely transferred

Question 14

resonance structures

Answer 14

two or more Lewis structures for the same molecule
write out both structures with double headed arrow between
only resonance hybrid structures exist in nature

Question 15

formal charge

Answer 15

charge the atom would have if all bonding electrons were shared equally

Question 16

formal charge formula

Answer 16

formal charge = # of val electrons - (# of lone pair electrons + 1/2# of bonding electrons

Question 17

how to determine most appropriate skeletal structure or resonance structure

Answer 17

1. sum of all formal charges in neutral molecule must be 0
2. sum of all formal charges in ion must equal charge of ion
3. small or zero formal charges on individual atoms are better than large ones
4. when formal charge can’t be avoided, negative formal charge should be on most electronegative atom

Question 18

odd electron species

Answer 18

molecules or electrons w/ odd # of electrons (called free radicals)
can’t write a good Lewis structure for these, but generally don’t exist in nature

Question 19

incomplete octets

Answer 19

Boron = only has 6 electrons`

Question 20

expanded octets

Answer 20

any element in third row and beyond usually have up to 12 (sometimes 14) electrons
typically octets are expanded to lower formal charge

Question 21

bond energy

Answer 21

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

Question 22

exo vs endo bonds

Answer 22

break bonds = endothermic (positive)

form bonds = exothermic (negative)

Question 23

Delta H of reaction formula

Answer 23

sum of bonds broken + sum of bonds formed